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Stress–Relaxation Properties of Mixograph Semolina–Water Doughs from Durum Wheat Cultivars of Variable Strength in Relation to Mixing Characteristics, Bread- and Pasta-making Performance
Abstract
Stress–relaxation behaviours of Mixograph semolina–water doughs prepared from Canadian durum wheat cultivars with diverse gluten strength were investigated and related to mixing characteristics, large deformation properties, and bread- and pasta-making quality. Semolina from «strong» (S) and «moderately strong» (MS) durum wheat cultivars required a longer Mixograph mixing time (4–5 min) and higher work input (140–196 Arbitrary Units) to mix to peak dough resistance (PDR) than «weak» (W) and «very weak» (VW) durum cultivars (2–3 min and 80–117 AU). Extensigraph maximum resistance to extension (Rmax/E ratio) and Alveograph P/L (tenacity to length ratio) values were higher for doughs from S cultivars than for MS, W, and VW cultivars. Doughs from S cultivars exhibited higher storage modulus (G′) and lower tan δ values at all frequencies, and slower rates of stress relaxation as compared to MS, W, and VW cultivars. Stress relaxation (times to relax 50% (t50) and 75% (t75) of initial stress) indicated that stronger doughs, which had higher proportions of glutenins, took longer to reach these iso-relaxation states, regardless of their initial relaxation modulus value. The parameters t50and t75were also strongly correlated with dough mixing properties, Extensigraph Rmax/E, Alveograph P/L, mixing energy, mixing time and loaf volume obtained by a long and a short bread-making process. However, for S cultivars loaf volume was 10 to 20% lower than that expected of bread wheat of comparable protein content. Stress relaxation data demonstrated no simple correlation to pasta cooking quality indicating that stronger gluten did not translate into a superior pasta cooking quality. Results are interpreted in the context of multimodal networks and transient networks with reversible crosslinks.
... Kernels subjected to constant deformation of 0. orientation of gluten in the dough. Rao et al (2001) indicated that stronger semolina-water doughs prepared from durum wheat with higher proportions of glutenins took longer stress relaxation (times to relax 50% [t 50 ] and 75% [t 75 ] of initial stress) to reach the isorelaxation states (42.3-50.1 sec), compared with intermediate doughs (20.0 sec) and very weak dough (8.4-11.3 sec), regardless of the initial relaxation modulus value. ...
... The strong interactions were present at longer relaxation times (τ 3 and τ 4 ). Rao et al (2001) and Li et al (2003), using a rheometer, indicated that doughs exhibited a characteristic bimodal distribution of relaxation times, with the second peak clearly discriminating between cultivars with varying strength and quality, which reflected the differences in the molecular weight distribution of glutenin polymers. Hernández et al (2012), evaluating stress relaxation of wheat kernels with HMW-GS and LMW-GS, suggested that these interactions were stronger in glutenin subunits with good breadmaking quality, that is, Glu-A1 2* and Glu-A1 5 + 10, compared with Glu-A1 null. ...
... The first and second Maxwell elements were mainly related to rheological properties, although the relaxation time (τ 2 ) at about 13-16 sec showed a positive effect on loaf volume. Rao et al (2001) also reported similar results in semolina-water doughs prepared from durum wheat, in which the parameters t 50 and t 75 were also strongly correlated with dough mixing properties, extensigraph R max /E, alveograph P/L, mixing energy, mixing time, and loaf volume obtained by a long and a short breadmaking process. a *, **, and *** are significant at P < 0.05, 0.001, and 0.0001, respectively; ns = not significant. ...
The stress relaxation behaviors of soft and bread-type wheat kernels were studied using the generalized Maxwell model. The data showed two phases, a fast phase at short times of about 1.52-16.88 sec (1 and 2) and a slow phase with longer times of about 81.28-793.81 sec (3 and 4). The shorter decay of ν1 can be explained by very weak forces that affect mainly the rheological properties. The slow decay (4) located at longer relaxation times resulted from strong forces. The first derivative obtained from the stress relaxation curve of intact wheat kernels was quite similar in shape to the dough farinograms. The stress relaxation parameters showed differences in springs, relaxation times, and viscosities of bread wheat compared with soft-type wheat kernels. The stresses 1ν and 4ν were correlated with wheat kernel, flour, rheological, and breadmaking properties; so especially were the elasticity of the spring (ν0) and viscosity of the fourth Maxwell element (η4), which were significantly correlated with all the quality properties, whereas ν2, ν3, η1, and η2 did not show correlation at all, except that ?2 was correlated with falling number and volume of CO2.
... An alternative strategy to minimize the effects of deformation history has been to ignore a portion of the stress relaxation curve, deemed the most affected region of the samples resulting from the deformation history, following constant-strain deformation. This concept was employed to evaluate the stress relaxation curves of wheat flour doughs by Rao et al. (2001) and Li et al. (2003) by neglecting the relaxation data falling after a time equivalent to half the loading time. Alfrey and Doty (1945) and Cunningham and Hlynka (1954) approach to this problem was to disregard an arbitrarily short period of time (comparable to the loading time) following sample loading. ...
... Allocating fewer terms to the Prony series gave poorer fits (results to shown). The kernel function employed shared exponential terms for both the loading and the constant-strain deformation steps (i.e., Steps 1 and 2), allowing Chen's model to be regarded as an improvement over previous methods (Alfrey and Doty, 1945;Cunningham and Hlynka, 1954;Matsumoto, 1979;Peleg, 1979;Peleg and Normand, 1983;Rao et al., 2001) to model the viscoelastic foods (e.g., oriental noodles) via stress relaxation testing. ...
... While three peaks (or more strictly three shoulders) can be clearly discerned in the CWRS noodles, the second peak (or second shoulder) was less pronounced for the CWAD noodles. In studies where wheat flour dough was subjected to shear deformation regimes, two stress relaxation processes had been observed, the first occurring at relatively short times (<1 s) and the second one over a wider (and longer) time span (10-1000 s) (Bohlin and Carlson, 1981;Li et al., 2003;Rao et al., 2001). Unlike wheat flour dough, the polymeric structure of cooked YAN was therefore defined by an additional molecular process. ...
Established methods that model stress relaxation (SR) behaviour in foods are regarded as semi-empirical due to their inability to account for the relaxation occurring at loading on the food’s early relaxation response. This report assessed a hereditary function based on a four-term Prony series to model the effect of deformation history on the SR behaviour of yellow alkaline (Chinese) noodles (YAN). YAN were manufactured from red spring (CWRS) and amber durum (CWAD) wheat flours, with or without cysteine (200ppm), so that YAN with distinct viscoelastic behaviour could be obtained. Results showed that the hereditary function successfully described the varying-strain and constant-strain response of YAN. CWRS noodles were firmer but had a lower elastic-like behaviour than CWAD noodles. SR spectra showed that cysteine weakened the mechanical behaviour of CWRS YAN possibly by lowering the molecular weight of its underlying protein network. Cysteine had little effect on the mechanical properties of CWAD YAN.
... Li et al. [25] indicated that the relaxation properties of dough depended on its gluten protein. Dough from strong wheat cultivar exhibited slower rates of stress relaxation and higher storage modulus as compared to moderate, weak, and very weak cultivars [26]. Wiechert model has been used to study the viscoelasticity of solid foods [17,19]. ...
... The result of stress relaxation in this study was similar to the study [17] that 9 % lemon fiber-enriched mantou had less elasticity than control mantou. Some papers studying the viscoelastic properties of wheat dough and gluten indicated that a slower (long) relaxation time was associated with good baking quality [26,27]. For dough and gluten, rapid relaxation times (0.1-10 s) were related to small polymer molecules, whereas longer relaxation times (10-10,000 s) were related to high molecular weight polymers [28]. ...
Mantou (steamed bread) is a Chinese fermented wheat product that is cooked in steamer. Whole wheat flour (WWF) is healthier than regular wheat flour (WF). This study investigated the physicochemical properties of dough and mantou made from WF and/or WWF. Results showed that the substitution of WF by WWF resulted in stiffer and less extensible dough. Both Peleg–Normand and Wiechert models fitted well to the stress relaxation data of mantou. Increasing the substitution level of WWF led to the decrease of
... Figueroa et al. (2013) compared the dough stress relaxation and same technique of compression in intact wheat kernels. They found that relaxation time of the dough at 0.45 s of the first decay, 3.2 s of the second decay and 24 s of relaxation time to third decay and reach the quasi steady-state of the dough, similar to that reported by Li et al. (2003) of <1-10 s of relaxation and quite close to the relaxation times (s 1 ) of durum dough reported (Rao et al., 2001). This is probably the reason that relaxation time required for dough as reported (Rao et al., 2001;Li et al., 2003;Figueroa et al., 2013), is shorter than s 1 and larger than s 4 observed for wheat kernels . ...
... They found that relaxation time of the dough at 0.45 s of the first decay, 3.2 s of the second decay and 24 s of relaxation time to third decay and reach the quasi steady-state of the dough, similar to that reported by Li et al. (2003) of <1-10 s of relaxation and quite close to the relaxation times (s 1 ) of durum dough reported (Rao et al., 2001). This is probably the reason that relaxation time required for dough as reported (Rao et al., 2001;Li et al., 2003;Figueroa et al., 2013), is shorter than s 1 and larger than s 4 observed for wheat kernels . Figueroa et al. (2013) found retardation time (k 1 ) of doughs with values of 0.4 s for good breadmaking quality and 0.5 s for poor quality and retardation time k 2 values were 8.8 and 10.7 s for good and poor quality, respectively. ...
... The relaxation time (s 3 ) showed significant differences between most of the high and low b-glucan barley cultivars. Using different equipments, several researchers reported similar relaxation times in hull-less barley kernels (Bargale and Irudayaraj, 1995), wheat kernels (Figueroa et al., 2011Hernández et al., 2012), gluten (Dobraszczyk and Morgenstern, 2003;Li et al., 2003) and doughs (Rao et al., 2001). Bargale and Irudayaraj (1995) reported relaxation times of 1.29, 4.42 and 14.2 s for s 1 , s 2 and s 3 , respectively, for barley kernels with about 10.1% moisture content and 6% strain. ...
... The relaxation times s 3 reported by Hernández et al. (2012) were high for wheat genotypes with high SDS-sedimentation volume and long mixing time. Rao et al. (2001) indicated that stronger doughs with higher proportions of glutenins, took longer stress relaxation to reach the iso-relaxation states (42.3e50.1 s) compared to intermediate doughs (22.3e20.0 s) and very weak doughs (8.4e11.3 ...
The stress relaxation behaviour of barley kernels with differences in β-glucan was studied using the generalized Maxwell model for explaining the differences in quality. The relaxation moduli show that cultivar significantly affected the relaxation times (τ2 and τ3) and compressional viscosity (ηE2 and ηE3) of the 3 Maxwell elements and the pure elastic component (E0). These data were twice as high in cultivars with high β-glucans compared to low β-glucans. Protein and malt extract, as well as β-glucan, showed similar patterns to the corresponding cultivars from the same locations. Malt extract was correlated with both insoluble fibre (−0.71; P < 0.0007) and total fibre (−0.66; P < 0.006). High β-glucan cultivars presented relatively high soluble fibre, wort viscosity and presented higher relaxation times. Soluble fibre and the wort viscosity were correlated with relaxation times τ1, τ2, τ3. Also, β-glucans were correlated with τ3 and viscosity ηE3. The overall importance of the effect of β-glucans on viscoelasticity, malting and food quality as shown in this investigation is in agreement with earlier investigations.
... There is general agreement that durum wheat baking performance improves as gluten becomes stronger, but remains inferior to bread wheat (Edwards et al., 2007). However, very strong gluten durum wheat has a tendency to exhibit tenacious gluten, imparting inextensible dough and lower loaf volume due to reduced oven response (Ammar et al., 2000;Edwards et al., 2001;Quaglia, 1988;Rao et al., 2001). Together, these results suggest that to develop durum wheat cultivars with loaf volumes (LV) approaching that of bread wheat, it may be necessary to achieve an appropriate balance of resistance to extension and extensibility in conjunction with increased overall strength (Dexter et al., 1994). ...
... However, the bread wheat checks were included to provide a baseline reference for the bread-making potential of high quality bread wheat cultivars. Ammar et al. (2000), Edwards et al. (2001), and Rao et al. (2001) suggested that gluten strength and dough extensibility are most important to the enhanced baking quality of durum wheat. In this study, correlation analyses between LV and dough extensibility was significant and confirmed that more extensible dough were important to LV potential in durum wheat. ...
Durum wheat (Triticum turgidum L. var. durum) is used predominantly for pasta products, but there is increasing interest in using durum for bread-making. The goal of this study was to assess the bread-making potential of 97Emmer19, an Emmer wheat (Triticum turgidum L. var. dicoccum) and in breeding lines derived from crosses of 97Emmer19 with adapted durum wheat cultivars. 97Emmer19 and its progeny were evaluated in 2005 and 2006 along with five durum wheat cultivars. Three bread wheat (Triticum aestivum L.) cultivars were included as checks to provide a baseline of bread making quality observed in high quality bread wheat cultivars. 97Emmer19 exhibited higher LV than all the durum wheat checks and approached the LV achieved with the bread wheat cultivar ‘AC Superb’. Breeding lines derived from 97Emmer19 had higher LV than those of the durum wheat checks, confirming that this trait was heritable. In general, durum wheat cultivars with elevated gluten strength and/or increased dough extensibility were noted to have higher LV. Dough extensibility appeared to be a more critical factor as gluten strength increased. These results indicate that there is potential to select for genotypes with improved baking quality in durum breeding programs.
... Bohlin and Carlson (1980) using a rheometer showed relaxation times of dough of 1 and 100 s, and in modified gluten of 1 and 500 s (Mita and Bohlin, 1983) attributable to the structural orientation of gluten in the dough. Rao et al. (2001) indicated that stronger dough of semolina-water from durum wheat which had higher proportions of glutenins, took longer to reach the iso-relaxation states about 42.3e50.1 s, compared to intermediate 22.3e20 s and very weak dough with 8.4e11.3 s. ...
... The third term with a range of relaxation times of about 40e60 s had a major contribution to the quality (Table 4). Rao et al. (2001) also reported similar results in semolina-water dough from durum wheat where the parameters t 50 and t 75 were correlated with dough mixing properties, extensigraph R max /E, alveograph P/L, mixing energy, mixing time and loaf volume. ...
... As Singh and MacRitchie (2001) pointed out, dough is a concentrated and polydisperse polymer system. Rao et al (2001) suggested that stress relaxation measurements would apply to hydrated gluten even though the degree of flexibility of its molecular structure is not well known because the relaxation modulus will reflect both entropic elasticity due to entanglements and enthalpic contributions due to physical cross-links. Furthermore, it was reported that the molecular entanglement of HMW glutenin polymers in dough under large deformation could give rise to strain hardening, which has been shown to be important in determining the strength of dough and stability of gas cells in breadmaking dough during proving and baking expansion (Dobraszczyk and Roberts 1994;Dobraszczyk 1999;Dobraszczyk et al 2003). ...
... The rapid application of strain (5% with a rise time of 0.1 sec) can give rise to inertial effects such as force oscillations that can distort the data and lead to an inaccurate relaxation spectrum at short times. Data below half of the rise time (0.05sec in this case) probably do not represent the true distribution of relaxation times (Rao et al 2001). Therefore, the G(t) and H(t) at times <0.05 sec were plotted by a light line and the test time 0.05 sec was indicated by a vertical arrow at 0.05 sec in Figs. ...
Cereal Chem. 80(3):333-338 Relaxation behavior was measured for dough, gluten and gluten protein fractions obtained from the U.K. biscuitmaking flour, Riband, and the U.K. breadmaking flour, Hereward. The relaxation spectrum, in which relaxation times ( ) are related to polymer molecular size, for dough showed a broad molecular size distribution, with two relaxation proces- ses: a major peak at short times and a second peak at times longer than 10 sec, which is thought to correspond to network structure, and which may be attributed to entanglements and physical cross-links of polymers. Relaxation spectra of glutens were similar to those for the corresponding doughs from both flours. Hereward gluten clearly showed a much more pronounced second peak in relaxation spectrum and higher relaxation modulus than Riband gluten at the same water content. In the gluten protein fractions, gliadin and acetic acid soluble glutenin only showed the first relaxation process, but gel protein clearly showed both the first and second relaxation processes. The results show that the relaxation prop- erties of dough depend on its gluten protein and that gel protein is responsible for the network structure for dough and gluten.
... For polymers of high molecular weight like gluten, LVP is being increasingly viewed as a method of molecular characterisation due to the difficulties of solubilising and separating very large polymers. Mechanical tests like frequency sweeps and long time creep compliance tests performed in the linear viscoelastic region have been increasingly used to examine the mechanical properties of cereal dough (Rao et al. 2001). This approach is now allowing more definite conclusions about the chemical nature of the network structure in dough and its relationship to end product quality. ...
... The baking strength index (an indicator of loaf volume potential at a given protein) values obtained are lower than for common wheat, typically of 100. The strong durum exhibited 2 Pasta-related physical dough properties and pasta texture for durum wheat varieties of variable gluten strength (adapted from Rao et al. 2001). higher P/L ratios than common wheat, indicative of a less extensible dough. ...
Durum wheat (Triticum turgidum L.) is the preferred raw material for the production of pasta worldwide and some speciality bread common in parts of Italy and the Mediterranean region. The quality of such foods in terms of texture, colour, flavour and appearance are determined by raw material quality, processing methods and other ingredients. This review focuses on the raw material composition and how these influence the dough characteristics and the end product quality. Protein has been known as an important component having an influence on the quality of pasta and bread. The glutenin and gliadin proteins, the types present and their ratio have been shown to influ-ence dough properties. Attempts to increase the number of high molecular weight glutenin subunits to obtain more varied dough proper-ties has the potential to improve the breadmaking properties of durum flour. Starch is more than an inert filler and recent research has shown the affect of varying the amylose content and ratio of large to small starch granules on pasta quality can be significant. Potentially new durum germplasm could be created and used in new food products. Other minor components like non-starch carbohydrates and lipids have received less attention. The former can have a large impact on the water absorption of durum flours and alter dough properties. Enzymes like lipoxygenase and polyphenol oxidase together with the lipid yellow pigments strongly impact the appearance of pasta foods. The results of recent research about these components on both pasta and bread quality using durum wheat are discussed.
... In a stress relaxation study of durum doughs made from six cultivars of different glutenin sub-unit composition, but with flour protein contents of very similar values, Rao et al. (2001) showed that the shear stress relaxation modulus decreased in step with the drop in protein quality (assessed as loaf volume per unit protein content of the flour). In contrast, Safari-Ardi & Phan-Thien (1998) observed that stress relaxation modulus values did not differ for breadmaking wheats of contrasting breadmaking properties (and protein content varying from 10 to 13 %). ...
Nitrogen supplied to wheat crops to increase grain productivity is being scrutinized because of its role in greenhouse gas emissions. Nitrogen affects food quality as well as food security because it increases grain protein content and can change wheat protein composition, both of which affect the rheological properties of dough made from the grain. This review explores the relationship between nitrogen functionality, wheat protein content and the ratio of gliadins to glutenins through critical assessment of recent studies on nitrogen fertilization of wheat. Moreover, by studying how variations in protein content and the gliadins/glutenins ratio affect the shear and extensional rheological properties of the dough, this review elucidates the direct role of nitrogen on wheat flour dough behavior during processing because process operations primarily employ extensional and shear forces. Nitrogen uptake by wheat plants leads to an increase in wheat protein content and changes in the gliadins/glutenins ratio. Confounding factors associated with wheat plant growth and dough preparation make it difficult to definitively separate effects of wheat protein content from effects of wheat protein composition on dough rheology. Nevertheless, in general, higher protein content is associated with larger gliadins/glutenins ratios, resulting in wheat flour doughs that are more extensible.
... Dry pasta is considered one of the most staple foodstuffs in the world due to its versatility, ease of cooking and storage, good nutritional quality and low cost (Bustos, Perez, & Leon, 2015;Rakhesh, Fellows, & Sissons, 2015). Durum wheat semolina represents the ingredient for the manufacture of superior pasta products because of high content of yellow pigments (carotenoids) and proteins, and inextensible and strong gluten of doughs (Rao, Mulvaney, Dexter, Edwards, & Peressini, 2001;Sissons, 2008). ...
Psyllium seed husk (PSH) is a soluble dietary fibre with interesting health benefits, including reduction in blood glucose level in subjects with type 2 diabetes. Its supplementation in pasta represents a challenge due to a negative impact of high PSH levels on product acceptability. The aim of this work was to investigate the effects of the substitution of semolina with different levels of PSH on cooking properties, microstructure and in vitro glycaemic response of pasta. Dry pasta samples enriched with PSH were produced by replacing durum wheat semolina with 25, 50, 75 and 100 g/kg PSH. Cooked enriched pastas were firmer and sticker than the control. Cooking loss increased with increasing PSH levels above 25 g/kg with values below the technological acceptable limit of 80 g/kg. Semolina substitution with 50–100 g/kg psyllium was effective in lowering the predictive glycaemic response of enriched pasta in comparison with the control. Scanning electron microscopy and dough rheology (dynamic frequency and temperature sweep tests) suggested that this decrease was related to the formation of fibre aggregates limiting starch swelling. Semolina replacement with 50 g/kg PSH has the potential to provide a health benefit with minimal impact on cooking features of functional pasta.
... Doughs exhibited a characteristic bimodal distribution of relaxation times, with the second peak clearly discriminating between cultivars with varying strength and quality, which reflects the differences in the MW distribution of glutenin polymers (Rao et al., 2001;Li et al., 2003). The second relaxation peak is related to the entanglement properties of high molecular weight insoluble glutenin polymers, and has been shown to be directly related to the insoluble fraction of the high MW glutenins (Li et al., 2003). ...
The rheological mechanisms important in breadmaking
... 9,12,13 Protein content is classified as typical when between 11% and 16%, 14,15 while gluten strength is primarily a function of the density of reversible disulfide bonds, which are responsible for the desired solid-like behaviour in cooked pasta. [15][16][17] Pasta should release minimal material into the cooking water and must be firm and not unduly sticky when cooked for maximum consumer acceptance. 2,18,19 Stickiness is one of the most desired quality parameters and it is related to the amount of amylose leached from the gelatinized starch granules. ...
BACKGROUND
Professional pasta cookers are filled with fresh water. The solids leached from the cooked pasta make pasta less firm and stickier while leading to water properties changes and overflow. The added fresh water has to be then reheated. The effect of continuous cooking on cooked pasta quality and water properties was investigated for the first time by simulating professional pasta cooking on a laboratory‐scale.
RESULTS
Continuous cooking procedure of 12 batches led to a solid content of cooking water of 37 (g kg‐1) resulting in an increase in shear‐thinning behaviour and consistency index. Pasta cooking loss decreased from 52.7 to 35.7 (g kg‐1) due to the lower water concentration gradient through the pasta. This was confirmed by the decrease in swelling index from 2.0·10‐3 to 1.6·10‐3 (g kg‐1) during the optimal cooking time (13 min 45 s). Surprisingly, continuous cooking made the pasta firmer while stickiness did not significantly differ (p ˃ 0.05).
CONCLUSION
Taking batch number 7 as the acceptability threshold, further studies are required to find an optimal solution for retaining cooking water properties highly affecting daily cooking procedures in food service kitchens.
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... Genetically, durum wheats are tetraploids and are lacking the D-genome found in hexaploid common wheats, which is believed to code for the high molecular weight glutenin polypeptides. Differences in pasta-making performances between durum and common wheat doughs may be due to differences in the distribution of polypeptide chain lengths and their associated reversible cross-links and possibly, entanglements [3,4]. These differences in turn, would have complex effects on dough strength and extensibility. ...
Durum wheat is the raw material of choice for the manufacture of superior quality pasta products. However, in some parts of the world many pasta producers have to use common wheat to make pasta, which shows a deficiency with respect to quality attributes. In this respect, the functionality of different hydrocolloids in a weak common wheat flour was investigated as a comparative study with the objective to improve pasta-making potential under industrial processing conditions. Six commercial hydrocolloids, sodium alginate (AL), propylene glycol alginate (PGA), xanthan gum, carrageenan, locust bean gum or guar gum were added to wheat flour at 0.5% and 1% substitution. A rheological investigation, based on dynamic small strain tests and large deformation tests (farinograph and amylograph analyses) was performed to evaluate differences in dough structure due to interactions between flour components and hydrocolloids, and related to cooking properties of pasta. All hydrocolloids promoted an increase in elastic interactions in the dough. The strongest doughs were obtained by addition of alginates. Only cooked pasta supplemented with AL, PGA and XG showed an increase in firmness compared with the reference (PGA > AL > XG). The product enriched with 0.5% PGA or 1% AL gave the highest overall acceptability and sensory scores. On the contrary, xanthan gum, carrageenan, locust bean gum or guar gum performed relatively poorly in flour. On the basis of these results alginates were the most effective improvers of pasta quality among different hydrocolloids.
... The rapid application of strain (5% with a rise time of 0.1 sec) can give rise to inertial effects such as force oscillations that can distort the data and lead to an inaccurate relaxation spectrum at short times. Data below half of the rise time (0.05 sec in this case) probably do not represent the true distribution of relaxation times [8]. Therefore, the G(t) and H((τ) ) at times <0.05 sec were plotted by a light line and the test time 0.05 sec was indicated by a vertical arrow at 0.05 sec in Figs.1-6. ...
... This is the first study of using different mathematical models to describe the viscoelastic properties of sponge cakes to our knowledge. Dough from strong wheat cultivar exhibited slower rates of stress relaxation and higher storage modulus as compared to moderate, weak, and very weak cultivars [34]. The relaxation time of bran-enriched spaghetti was affected by cooking time [6]. ...
Stress relaxation has traditionally been employed as one of the principal means for measuring the viscoelastic behavior of foods. In this study, first the quinces slices were dried in an infrared—hot air dryer (375 W, 60 °C and 1 m/s flow rate). The effects of quince powder substitution (0, 5, 10, 15 and 20%) on stress relaxation and textural parameters of sponge cakes were evaluated by the Texture Analyzer. The results showed that mechanical stress relaxation data of quince sponge cakes were fitted well by both the Peleg-Normand and four-element Maxwell models. The initial force (F0) and percentage stress relaxation (%SR) parameter of quince sponge cakes increased with increasing substitution. Generally, increasing the substitution of flour by quince resulted in less elasticity and higher hardness of sponge cakes. The elasticity of the sponge cakes was the lowest at 20% substitution of quince powder. The consistency and hardness values of baked cakes increased with increasing quince powder levels, whereas the cohesiveness, resilience and chewiness of samples showed a reverse trend.
... Wheat proteins and starch properties are known to affect pasta quality (Cubadda et al. 2007;D'Egidio et al. 1990;Delcour et al. 2000a,b;Dexter et al. 1983;Grant et al. 1993;Oak et al. 2006). Pasta cooking quality is generally related to both protein content and gluten strength of durum wheat (Ames et al. 2003;D'Egidio et al. 1990;Malcolmson et al. 1993;Rao et al. 2001). A higher protein content (higher vitreousness in the wheat kernel) has been associated with an improved pasta cooking quality in terms of textural parameters (firmness and stickiness; Dexter and Matsuo 1977). ...
... This is the first study of using different mathematical models to describe the viscoelastic properties of steamed bread to our knowledge. Dough from strong wheat cultivar exhibited slower rates of stress relaxation and higher storage modulus as compared to moderate, weak, and very weak cultivars (35) . by cooking time (21) . ...
Wheat bran is one of the major dietary fiber sources widely used in the food industry in order to produce fiber-enriched foods. The effects of wheat bran substitution (0-30%), water absorption (46-62%) and electric power (4-12 kW) of steamer on stress relaxation and textural parameters of steamed breads were evaluated by the Texture Analyzer. The results showed that mechanical stress relaxation data of steamed breads were fitted well by both the Peleg-Normand and three-element Maxwell models. At 10-40% strains tested, common and bran-enriched steamed breads were more elastic measured at low strain. It was suitable to perform the stress relaxation test of steamed bread at 10-30% strains. Generally, increasing the substitution of flour by bran resulted in less elasticity and higher hardness of steamed bread. Results of sensory evaluation indicated no significant difference in textural and overall acceptability among various steamed breads with 0, 10 and 20% of wheat bran. Medium and high water absorptions (54-62%) produced fiber-enriched steamed bread with better elasticity and texture. The elasticity of the steamed bread was the lowest at 4 kW electric power of steamer. Significant correlations were found between textural characteristics and stress relaxation parameters. This study suggests that 20% bran-enriched steamed bread, with better elasticity and sensory acceptability, can be produced at 54% of water absorption and 12 kW of electric power of the steamer.
... The rapid application of strain (5% with a rise time of 0.1 sec) can give rise to inertial effects such as force oscillations that can distort the data and lead to an inaccurate relaxation spectrum at short times. Data below half of the rise time (0.05 sec in this case) probably do not represent the true distribution of relaxation times (Rao et al., 2001). Therefore, the G (t) and H (τ) at times <0.05 sec were plotted by a light line and the test time 0.05 sec was indicated by a vertical arrow at 0.05 sec in Fig. 1 to 7. Fig. 1 and 2 and the corresponding relaxation plotted are shown in Fig. 3 and 4. From the relaxation curves and relaxation plots for these MCT, LCT and Butter doughs, three relaxation processes were distinguished over the whole relaxation time: one occurring at short relaxation times and another occurring the longer relaxation times from 10 0 to 10 3 sec. ...
This study investigates the stress relaxation behavior of gluten and bread dough with Medium-Chain Triacylglycerols (MCT), also, comparison with Long-Chain Triacylglycerols (LCT) and Butter. Dough and guten obtained from strong with LCT and Butter, there had a higher G (t) and H (Τ) over the whole relaxation time than those from the MCT dough. This indicates that it has a stronger network structure. He stress relaxation curves of gluten with MCT, which effect of temperature was not observed most of the time. On the other hand, in the case of butter and LCT, changes were observed in the relaxation curve temperature rises both. Results from these, it has a useful functionality to network formation of gluten has been clarified that MCT.
... The shortening added produces a lipid plasticization of gluten and modifies or competes with the interactions of endogenous components. In high content fat dough (more than ~5 %), the fat added appears to saturate the system and only a part of the added lipid can exert a plasticizing effect (23). One portion of the water incorporated will be an integral part of the dough and another will act as a plasticizer. ...
The eff ect of protein composition and content on the characteristics and properties of
laminated baked products has been studied for a long time. However, there are no fl our
quality parameters related to its suitability to produce yeast-leavened laminated salty
baked products. The relationships among fl our characteristics, laminated dough pieces
and baked products were studied in order to establish fl our quality parameters and help
predict the quality of the products. Yeast-leavened salty laminated products made with
hard wheat fl our had bett er quality properties than the products made with soft wheat
fl our. Hydrophilic components and a high gluten network quality are responsible for the
generation of a rigid structure and viscous dough. Consequently, during baking, the dough
rises rather than extends laterally and does not experience any change in the expected
shape. Among the analysed fl our characteristics, glutenin macropolymer content, lactic
acid and sodium carbonate solvent retention capacities together with dough viscosity and
resistance to deformation were the variables which infl uenced the most the quality of
yeast-leavened salty laminated products.
... Moreover the relationships among processing parameters and product quality are not fully understood [2,12,13,16]. The literature on pasta extrusion is quite limited and mainly focused on the raw material [15,11], drying process and quality of the final products [5,10]. In many researches, the main objective was the selection of the more appropriate durum wheat cultivars by evaluating their performance when processed in the available plants, or the measurement of the physicochemical changes experienced by the components [9]. ...
Rheological measurements were conducted on semolina doughs. Two doughs were considered, one directly taken from an extrusion plant and another mixed in lab conditions. A rotational viscometer was used in the plate-plate configuration. Creep tests were carried on too, to verify the possibility to neglect the elastic component of strain. It was investigated the influence of the temperature on the viscous behaviour of both doughs, while only on the lab mixed dough was tested the influence of moisture content. The aim of this research is the determination of a rheological model useful for a subsequent CFD analysis of the extrusion process.
... Wu et al [3] report that the addition of wheat bran increased the %SR value of steamed bread. Dough from strong wheat cultivars exhibited slower rates of stress relaxation and higher storage modulus, compared to moderate, weak, and very weak cultivars [33]. However, the particle size of PCF did not significantly affect the %SR of mantou (Table 2). ...
The consumption of dietary fiber offers the health benefit of lowering the risk of many chronic diseases. Pineapple core fiber (PCF) in this study was extracted and incorporated into dough and mantou (i.e., steamed bread). The effects of PCF substitution and fiber size on textural and rheological properties of dough and mantou were evaluated by a texture analyzer. The substitution of wheat flour by PCF resulted in a stiffer and less extensible dough with or without fermentation. The hardness and gumminess of mantou significantly increased as the PCF substitution increased from 0% to 15%, but the cohesiveness, specific volume, and elasticity significantly decreased with the fiber substitution. Ten percent PCF-enriched dough and mantou with various fiber sizes had similar rheological and textural properties, except for the k1 and k2 values. By sensory evaluation, 5% PCF-enriched mantou and the control bread had better acceptability in texture, color, odor, and overall acceptability, compared to mantous enriched with 10% or 15% PCF. Significant correlations existed between the rheological properties of dough and textural parameters of mantou and between the sensory quality and textural parameters of mantou. Therefore, we suggest that fiber-enriched mantou can be prepared with 5% PCF substitution to increase the intake of dietary fiber and maintain the quality of mantou.
... Le caratteristiche varietali influenzano marcatamente la qualità panificatoria. Come è noto la maggior parte delle moderne cultivar di grano duro sono state selezionate per l'attitudine pastificatoria e presentano generalmente un glutine poco tenace e poco estensibile, non particolarmente idoneo alla panificazione (Rao et al., 2001;Palumbo et al., 2002). In Italia, tuttavia, è stata condotta una notevole attività di miglioramento genetico (Boggini et al., 2003b) oltre che numerosi studi di confronto varietale relativamente alla qualità panificatoria (Palumbo et al., 2003) del frumento duro. ...
Data di presentazione: 8 febbraio 2006 Riassunto La qualità del frumento duro è un sistema complesso che comprende caratteristiche intrinseche del prodotto, re-quisiti del contesto produttivo e requisiti di garanzia. In questa rassegna si è focalizzata l'attenzione sugli aspetti tecnologici e nutrizionali della qualità del prodotto, in relazione alle influenze climatiche ed agronomiche. In parti-colare, la qualità tecnologica è stata indagata in funzione della tipologia del prodotto trasformato (pasta, pane, cou-scous, burghul). Sono stati valutati gli effetti dei principali e più indagati fattori ambientali (concimazione azotata e solfatica, temperatura e regime idrico) ed anche del metodo di coltivazione biologico sulla qualità del prodotto. Sono state esaminate, inoltre, le caratteristiche nutrizionali del frumento duro dovute al contenuto in proteine, ami-do, lipidi, vitamine, fibre e sali minerali. Particolare attenzione è stata rivolta alla capacità antiossidante, in grado di prevenire malattie croniche e degenerative. Questa risulta legata all'elevato contenuto in composti bioattivi, qua-li composti fenolici, tocoli, carotenoidi e fibre, presenti nella granella integrale di frumento duro. Alla luce dei nuo-vi orientamenti di politica comunitaria e del crescente interesse verso gli alimenti funzionali, infine, sono state pro-spettate due possibilità di sviluppo del comparto del frumento duro; queste riguardano: i) la qualificazione della materia prima, mediante il miglioramento dei requisiti tecnologici, nutrizionali e salutistici e lo sviluppo di prodot-ti certificati (IGP, DOP, biologici); ii) lo sviluppo di tecnologie di produzione e trasformazione che consentano un incremento nei livelli dei composti bioattivi nella granella e nei suoi derivati. Parole chiave: alimenti funzionali, composti bioattivi, couscous, frumento duro, influenza ambientale, pasta, qualità nutrizionale, qualità tecnologica.
... Dough properties and the resulting bread quality are influenced by several factors, and numerous scientific papers have described the effect of different types of mixers, mixing speed, temperature and ingredients, on the properties of wheat doughs (Chin & Campbell, 2005a,b;Connelly & McIntier, 2008;Ktenioudaki et al., 2010). To our knowledge, only a few researches have been carried out on the behaviour of doughs made with semolina of different extraction rate, during the mixing process (Rao et al., 2001). Moreover, the dough samples have been prepared by means of the Chopin Consistograph mixer, and the Chopin Consistograph has never been used to measure key mixing variables and to correlate them with dough properties and leavening performances. ...
Partial least square regression analysis was used to study the correlation between X variables (semolina quality, hydration level and mixing time) and Y variables, which were, in a first model, dough consistency during mixing, and, in a second model, dough properties after mixing (strength, elasticity, density) and leavening (maximum volume). The first model showed a predictive residual sum of squares (PRESS) of 2.98 and a predictive R 2 (Q 2) of 0.92, and highlighted the key role of hydration and mixing time on dough consistency. The second model had the best PRESS (8.25) and Q 2 (0.94) values for dough volume and indicated that the volume increased with increasing mixing time until the dough consistency decreased of 20–30%. Dough volume was primarily affected by hydration. The model indicated that maximum volume after leavening, corresponding to optimum mixing time, was obtained with a soft and elastic dough, with a low‐density value.
... Certainly under high-and ultrahigh-temperature pasta drying conditions, gluten strength has less influence on cooking quality than under low-temperature conditions (D'Egidio et al 1990;De Stefanis and Sgrulletta 1990). Gluten from a Canadian extra strong cultivar exhibit pasta cooking quality comparable to those of intermediate strength at equivalent protein (Rao et al 2001), indicating that gluten strength (gluten quality) is not as important as once thought. Sopiwnyk (1999) related the gluten strength of seven Canadian durum wheats to cooked pasta texture and found that pasta made from samples with weaker gluten strength did not necessarily result in pasta with poorer cooking quality. ...
The effects of varying the gluten composition at constant protein, protein content at constant composition, and glutenin-to-gliadin (glu/gli) ratio on durum semolina rheological properties and the quality of the spaghetti derived from these doughs was investigated using the reconstitution method. Reconstituted flours were built up from a common durum starch and water-soluble fraction but with varying gluten types from a range of wheats at both 12 and 9% total protein. A 10-g mixograph and microextensigraph properties were affected by the source of the gluten, which was related to glutenin composition and polymeric molecular weight distribution. Cooked pasta firmness was highly correlated to mixograph development time (MDDT). Furthermore, varying the protein content (9-20%) showed an increase in mixograph peak resistance (PR) with no effect on extensigraph Rmax. Pasta firmness increased and stickiness decreased with increasing protein content. In another experiment, the glutenin and gliadin fractions isolated from durum wheat were added to the respective base semolina to investigate the effect of varying the glu/gli ratio by 1.3-1.6 fold. Increasing the ratio increased MDDT but had no effect on PR and resistance breakdown. Variable effects were obtained for spaghetti firmness. The information obtained should prove useful to durum breeders by providing further evidence for the importance of protein to pasta quality.
... Doughs exhibited a characteristic bimodal distribution of relaxation times, with the second peak clearly discriminating between cultivars with varying strength and quality, which reflects the differences in the MW distribution of glutenin polymers (Rao et al., 2001;Li et al., 2003). The second relaxation peak is related to the entanglement properties of high molecular weight insoluble glutenin polymers, and has been shown to be directly related to the insoluble fraction of the high MW glutenins (Li et al., 2003). ...
The applications of rheology to the main processes encountered during breadmaking (mixing, sheeting, fermentation and baking) are reviewed. The most commonly used rheological test methods and their relationships to product functionality are reviewed.It is shown that the most commonly used method for rheological testing of doughs, shear oscillation dynamic rheology, is generally used under deformation conditions inappropriate for breadmaking and shows little relationship with end-use performance. The frequency range used in conventional shear oscillation tests is limited to the plateau region, which is insensitive to changes in the HMW glutenin polymers thought to be responsible for variations in baking quality. The appropriate deformation conditions can be accessed either by long-time creep or relaxation measurements, or by large deformation extensional measurements at low strain rates and elevated temperatures.Molecular size and structure of the gluten polymers that make up the major structural components of wheat are related to their rheological properties via modern polymer rheology concepts. Interactions between polymer chain entanglements and branching are seen to be the key mechanisms determining the rheology of HMW polymers. Recent work confirms the observation that the dynamic shear plateau modulus is essentially independent of variations in MW of glutens amongst wheat varieties of varying baking performance and also that it is not the size of the soluble glutenin polymers, but the secondary structural and rheological properties of the insoluble polymer fraction that are mainly responsible for variations in baking performance. Extensional strain hardening has been shown to be a sensitive indicator of entanglements and long-chain branching in HMW polymers, and is well related to baking performance of bread doughs. The Considere failure criterion for instability in extension of polymers defines a region below which bubble walls become unstable, and predicts that when strain hardening falls below a value of around 1, bubble walls are no longer stable and coalesce rapidly, resulting in loss of gas retention and lower volume and texture. Strain hardening in doughs has been shown to reach this value at increasingly higher temperatures for better breadmaking varieties and is directly related to bubble stability and baking performance.
... During the past decade, many attempts have been made to apply fundamental rheological methods to dough. Results have been reported for bread wheat dough (Amemiya and Menjivar 1992;Janssen et al 1996b), durum wheat dough (Kovacs et al 1994;Edwards et al 1999;Edwards et al 2001;Rao et al 2001), frozen bread dough (Kenny et al 1999), and rye dough (Autio et al 1999). However, dough is a complex system, generally consisting of a hydrated gluten matrix with embedded starch particles. ...
Cereal Chem. 80(5):587-595 The rheological properties of dough and gluten are important for end- use quality of flour but there is a lack of knowledge of the relationships between fundamental and empirical tests and how they relate to flour composition and gluten quality. Dough and gluten from six breadmaking wheat qualities were subjected to a range of rheological tests. Fun- damental (small-deformation) rheological characterizations (dynamic oscillatory shear and creep recovery) were performed on gluten to avoid the nonlinear influence of the starch component, whereas large defor- mation tests were conducted on both dough and gluten. A number of variables from the various curves were considered and subjected to a principal component analysis (PCA) to get an overview of relationships between the various variables. The first component represented vari- ability in protein quality, associated with elasticity and tenacity in large deformation (large positive loadings for resistance to extension and initial slope of dough and gluten extension curves recorded by the SMS/Kieffer dough and gluten extensibility rig, and the tenacity and strain hardening index of dough measured by the Dobraszczyk/Roberts dough inflation system), the elastic character of the hydrated gluten proteins (large positive loading for elastic modulus (G ), large negative loadings for tan and steady state compliance (Je 0 )), the presence of high molecular weight glutenin subunits (HMW-GS) 5+10 vs. 2+12, and a size distri- bution of glutenin polymers shifted toward the high-end range. The second principal component was associated with flour protein content. Certain rheological data were influenced by protein content in addition to protein quality (area under dough extension curves and dough inflation curves (W)). The approach made it possible to bridge the gap between fundamental rheological properties, empirical measurements of physical properties, protein composition, and size distribution. The interpretation of this study gave indications of the molecular basis for differences in breadmaking performance. The quality of a baked product depends on the properties of the dough during processing. Bakers assess the properties of the dough at various stages of the breadmaking process by subjective physical evaluations. Objective measurements of these properties were first developed by cereal scientists in the 1930's (Bloksma and Bushuk 1988). Such specialized equipment for dough testing as the farinograph, mixograph, extensigraph, and alveograph imitate the deformation experienced by the dough during proces- sing and provide measurements of the physical properties of the dough. They generally give good correlations with breadmaking performance, but as they are empirical, the results cannot be inter- preted in terms of material properties (Menjivar 1990). Studies on synthetic polymers show that fundamental rheo-
... A bimodal distribution of relaxation times in stress relaxation measurements may reflect a bimodal distribution of gluten or dough constituents: monomeric proteins (mainly gliadins) and polymeric proteins (glutenin polymers) (Mita and Bohlin 1983;Rao et al 2000;Rao et al 2001;Li et al 2002). The monomeric proteins have short relaxation times in the order of 1-10 sec, whereas the relaxation of polymers occurs at longer times, 10-10 4 sec. ...
Cereal Chem. 80(5):575–586 The rheological properties of fresh gluten in small amplitude oscilla-tion in shear (SAOS) and creep recovery after short application of stress was related to the hearth breadbaking performance of wheat flours using the multivariate statistics partial least squares (PLS) regression. The picture was completed by dough mixing and extensional properties, flour protein size distribution determined by SE-HPLC, and high molecular weight glutenin subunit (HMW-GS) composition. The sample set comprised 20 wheat cultivars grown at two different levels of nitrogen fertilizer in one location. Flours yielding stiffer and more elastic glutens, with higher elastic and viscous moduli (G and G) and lower tan d values in SAOS, gave doughs that were better able to retain their shape during proving and baking, resulting in breads of high form ratios. Creep recovery measurements after short application of stress showed that glutens from flours of good breadmaking quality had high relative elastic recovery. The nitrogen fertilizer level affected the protein size dis-tribution by an increase in monomeric proteins (gliadins), which gave glutens of higher tan d and flatter bread loaves (lower form ratio).
Background and Objectives
This study investigated the impact of protein quantity and gluten strength on mechanical properties and microstructure of cooked pasta using texture analyzer and scanning electron microscopy. Three Canadian durum varieties with wide range of gluten strength at four protein levels were selected.
Findings
Four distinct microstructures were characterized for cooked pasta. Pasta with firm texture exhibited compact and dense protein networks, while that with soft texture showed open, coarse, and heterogeneous structures. Protein content was the dominant factor in determining pasta firmness, the impact of gluten strength on pasta texture depends on protein content and cooking time. Greater impact from gluten strength was observed when pasta was overcooked.
Conclusions
The relative contribution of protein quantity and quality in cooked pasta texture depends upon the ranges of protein content, gluten strength, and degree of cooking.
Significance and Novelty
This study unveiled the impact of wheat protein content and gluten strength on textural and microstructural properties of pasta at three cooking times. Results generated from this study provide guidance for durum breeding programs, durum milling, and pasta processing industry in setting protein content and gluten strength targets to ensure pasta quality.
Background and objectives
Durum wheat (Triticum turgidum ssp. durum) (2n = 28, AABB) utilization is somewhat hampered by its weak and/or inextensible gluten. One strategy to overcome this limitation is through the introduction of the Glu-D1 alleles from bread wheat (Triticum aestivum) (2n = 42, AABBDD).
Findings
Several methods have been employed to introduce or transfer the Glu-D1 locus into durum wheat. These have included whole chromosome additions of 1D, substitutions of 1D for 1A or 1B, spontaneous and Ph1b-induced homoeologous recombination of bread wheat chromosome 1D with the 1A or 1B of durum, and genetic transformation using Glu-D1 Dx and Dy genes singly or together.
Conclusions
The introduction of whole 1D chromosomes has three main drawbacks, 1) instability of the n = 30 chromosome addition lines, 2) agronomic inferiority of 1D substitutions, and 3) lack of homologous pairing of 1D in subsequent breeding. Genetic transformation has shown limited utility as gene insertion and inheritance are not predictable, and consumer acceptance of genetically modified organisms is not wide-spread. Consequently, homoeologous recombination appears to be the most promising approach. Key considerations include 1) size of the 1D translocation, 2) substituted (loss, replacement) of a portion of 1A or 1B, and 3) utilization of Dx2+Dy12 vs. Dx5+Dy10, or other possible Glu-D1 alleles. In general, introduction of Glu-D1 increased dough strength and bread making quality. Glu-D1 Dx2+Dy12 seemed superior to Dx5+Dy10, as the latter produced excessively strong, inelastic doughs.
Significance and novelty
Durum wheat production and consumption will increase as bread quality improves. The Glu-D1 high molecular weight glutenin proteins will likely play a role in improving bread making ability.
The sponge and dough mixing process is one of the most common in the world, yet the mechanistic understanding of this process has yet to be sufficiently explored. In this study, aqueous solutions of ethanol, succinic acid, and their combination were prepared at concentrations intended to replicate fermentation times of 3, 4 and 6 h. These solutions were added to a farinograph mixer to make dough using hard wheat, soft wheat, and durum wheat flour. The results indicate that these yeast metabolites (ethanol, succinic acid) impact the mixing resistance, peak mixing value, and dough mixing stability in each of the flour types, likely primarily affected by the ratios of gliadin to glutenin and LMW glutenin in each flour type. Results suggest a stabilizing non-covalent interaction imparted by gliadin at peak mixing time, a stabilizing effect of HMW glutenin during break down, and synergistic effects of ethanol and succinic acid that leads to a faster rate of breakdown in later stages of mixing. It also suggests an increase in mixing resistance when acidulants are added to durum wheat dough. Taken together, this study adds new insights on the sponge and dough mixing process in a way that has not previously been conducted.
Background:
Triticale gluten still remains very poorly characterized rheologically. In this study the mechanical spectra of gluten isolated from four triticale cultivars were registered and fitted with Cole-Cole functions yielding the viscoelastic plateau parameters. Master spectra were calculated. Retardation test was performed and used to calculate the composite mechanical spectra and the width of viscoelastic plateau l. Protein fractional composition of triticale flour and gluten was studied using capillary zone electrophoresis.
Results:
Differentiated HMW-GS/SS compositions were identified in the studied triticale cultivars. The rheological parameters reached following values: JN(0) 1.05·10(-3) to 2.69·10(-3) Pa(-1) , GN(0) 372 to 956 Pa, ω0 0.003 to 0.06 rad/s, l 169 to 3121, Je(0) 1.57·10(-3) to 5.03·10(-3) Pa(-1) , Ge(0) 199 to 637 Pa and η0 1.06·10(7) to 3.93·10(7) Pa·s.
Conclusions:
Viscoelastic properties of triticale gluten correspond to the lower end of medium viscoelasticity shown by common wheat gluten. Master spectra and the composite mechanical spectra prove that four triticale glutens exhibit practically an identical type of viscoelastic behaviour of a biopolymeric viscoelastic liquid similar to wheat gluten. The viscoelastic plateau parameters GN(0) , JN(0) , ω0 and l appeared significantly correlated with the contents of prolamins and secaloglutenins in triticale flours and glutens.
The interrelationships between flour quality and the variability in the dough physical properties and bread loaf characteristics was investigated under reduced salt conditions using partial least squares (PLS) regression analysis. Seventy-two percent of the variability in dough physical properties was explained by the flour quality using a three-factor PLS model. Damaged starch content (DS), protein content and Farinograph dough development time (DDT) explained the variability of dough creep-recovery behavior along PLS-1. Farinograph absorption (FAB), located along PLS-2, was strongly related to dough adhesiveness, where adhesiveness was highly correlated to dough stickiness (r = 0.91). Eighty-nine percent of the variability in bread loaf characteristics was explained by the flour quality using a four-factor PLS model; the first 2 PLS-factors explained 66% of the variability. The loaf volume was related to a high number of loaf cells, whose expansion resulted in a greater loaf height. The relation between loaf volume and loaf height was expressed more in PLS-3 than PLS-1 and PLS-2. Mean cell wall thickness and mean cell diameter were closely related negatively along PLS-1, where DS and Farinograph dough stability explained much of the variability in these loaf characteristics. Along the third PLS-factor, FAB explained the variability in loaf weight.
Pasta is a traditional food with high consumer acceptance, characterized by its convenience, palatability, and nutritional quality. While the preferred ingredient to make pasta is durum wheat semolina (Triticum durum Desf.), this cereal grows under a relatively narrow range of climatic conditions, which makes it expensive, with low supply and availability. Therefore, it is common to find pasta made from bread wheat flour (Triticum aestivum L.), especially in those products consumed by people who prioritize price over quality. The product is still a good but would have some expected changes in cooking properties and appearance. Therefore, to study the differences between semolina and bread wheat pasta’s cooking properties, scanning electron microscopy, sensory evaluation, and instrumental texture were used to analyze commercial spaghettis made with both types of wheat. A brief discussion in relation to the role of raw material, including the bread wheat flour, together with the protein and starch behavior, salt, water, and pasta processing, was also presented. Despite the differences between both types of wheat and the resulting pasta, the convenience, availability, and preference tend to influence consumer choice.
Background:
The objective was to evaluate whether an ultrasonic reflectance technique has predictive capacity for breadmaking performance of doughs made from a wide range of formulation conditions. Two flours of contrasting dough strength augmented with different levels of ingredients (inulin, oil, emulsifier or salt) were used to produce different bread doughs with a wide range of properties. Breadmaking performance was evaluated by conventional large-strain rheological tests on the dough and by assessment of loaf quality. The ultrasound tests were performed with a broadband reflectance technique in the frequency range of 0.3-6 MHz.
Results:
Principal component analysis (PCA) showed that ultrasonic attenuation and phase velocity at frequencies between 0.3 and 3 MHz are good predictors for rheological and bread scoring characteristics.
Conclusions:
Ultrasonic parameters had predictive capacity for breadmaking performance for a wide range of dough formulations Lower frequency attenuation coefficients correlated well with conventional quality indices of both the dough and the bread.
The effects of dough moisture, mixing time, and cooking time on uncooked and cooked elbow macaroni by means of starch pasting and macaroni textural characteristics were investigated. In conventional elbow macaroni production, cooking time was found to have significant contributions to cooked macaroni starch pasting properties, indicating that degree of starch cook dependent on cooking time was the main influence on cooked macaroni starch pasting phenomena. Dough moisture also showed some significant (P < 0.05) relationships with cooked macaroni starch pasting properties; however, mixing time did not show significant effect. Cooked macaroni starch pasting properties showed significantly (P < 0.05) high correlations with cooked macaroni firmness and stickiness. Cooking time was the only major variable contributing to variations in cooked elbow macaroni starch and consequently in pasting and texture characteristics. Cooking time was highly related to firmness and stickiness of cooked elbow macaroni (P < 0.0001, R-2 = 0.8148; P < 0.0001, R-2 = 0.6215, respectively). In addition, dough moisture had a slight significant (P < 0.05) effect on cooked elbow macaroni firmness and stickiness. Cooked elbow macaroni firmness and stickiness were found to be highly correlated (P = 0.0001, R-2 = 0.8459). Increases in firmness increased cooked elbow macaroni stickiness. As a result, when elbow macaroni was cooked for shorter times, firmer and stickier macaroni was obtained.
Consumption of natural bioactive compounds such as polyphenols and dietary fiber offers health benefits. Lemon pomace, a by-product during processing of lemon juice, is discarded which contributes to environmental pollution. In the present study, lemon fiber (LF) was extracted from lemon pomace and incorporated into dough and Mantou. Results showed that the substitution of wheat flour by LF resulted in stiffer and less extensible dough with or without fermentation. Both Peleg-Normand and Wiechert models fitted well to the stress relaxation data of Mantou (R2 > 0.99). The parameters of two models were significantly affected by the amount of LF. The hardness of Mantou increased with the increasing of the LF substitution (0–9 g/100 g flour), but the cohesiveness, specific volume and elasticity decreased with the fiber substitution. Steaming led to significant decrease in free phenolics and increase in bound form of proofed dough. These results suggest that the substitution of 3 or 6 g LF per 100 g flour can produce healthy and acceptable Mantou with higher free total phenolic content and antioxidant capacity.
The bread-making characteristics of 23 Italian durum wheat cultivars grown in Sicily in 1998-1999 are reported. Protein content, farinograph curves, alveographic parameters, glutenin composition and semolina colour were determined and an experimental bread-making test was carried out. Environmental conditions strongly affected the qualitative characteristics of the varieties. All the technological evaluations showed a wide range of variation also among genotypes in all environments. Loaf volume was correlated with alveographic P/L. The new cultivars Colorado, Mongibello, Varano and Svevo are well suited for bread-making and are characterized by the "7+8" or "6+8" HMW glutenins.
Calamondin fiber ( CF ) was extracted and incorporated into dough and steamed bread. Results showed that the substitution of wheat flour by CF resulted in a stiffer and less extensible dough. Both P eleg– N ormand and W iechert models fitted well to the stress relaxation data of steamed bread. Hardness of steamed bread increased with the increase of CF substitution, but the cohesiveness, specific volume and elasticity decreased with the fiber substitution. As CF substitution was increased from 0 to 9%, total phenolic content and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical‐scavenging capacity of the steamed bread were improved by about 23 and 34, 52 and 53, as well as 77 and 74%, respectively. In sensory evaluation, steamed breads with 0–6% CF had similar flavor, texture and overall scores. These results suggest that the addition of 3 or 6% CF can produce healthy and acceptable fiber‐enriched steamed bread with higher phytochemicals and antioxidant capacity.
Practical Applications
Consumption of dietary fiber offers health benefits including lower risk for many chronic diseases. The increased consumption of steamed bread enriched with calamondin fiber is proposed for health reasons. Calamondin is one of citrus fruits, and its pomace contains some phytochemicals, such as fiber, phenolics and flavonoids. The calamondin fiber was extracted and could be supplied as a potential source of dietary fiber. The study demonstrated that fiber‐enriched steamed bread with good sensory and nutritional quality could be produced by the partial substitution of wheat flour by calamondin fiber.
The aim of this study was to assess the relationship between the physical and chemical parameters (ash, moisture, protein, wet gluten, gluten deformation index, gluten index, Falling Number index, maltose index and damaged starch) and Extensograph, Amilograph and Rheofermentometer rheological parameters by using the principal component analysis (PCA). There were significant correlations (p<0.05) between technological parameters such as protein content, wet gluten content, gluten deformation index and Extensograph extensibility values; between maltose index, Falling Number index and Rheofermentometer total volume of gaseous curve values; between technological parameters like protein content, wet gluten content and damaged starch, maltose index and Falling Number index, etc.
Pineapple peel fiber (PPF) was extracted and incorporated into dough and steamed bread. Results showed that the substitution of wheat flour by PPF resulted in stiffer and less extensible dough with or without fermentation. The hardness and gumminess of steamed bread increased with increasing the PPF substitution (0–15%), but the cohesiveness, specific volume and elasticity decreased with the fiber substitution. PPF-enriched steamed bread with large fiber size had significantly higher specific volume and elasticity as well as lower hardness than that with small fiber size. By sensory evaluation, the steamed breads with 0–10% PPF had higher acceptability in overall score (4.50–4.87) than that (3.45) of 15% PPF-enriched steamed bread. Significant correlations were found between rheological properties of dough and textural characteristics of steamed bread. Therefore we suggest fiber-enriched steamed bread can be prepared with 5–10% PPF substitution in order to increase the intake of dietary fiber.Practical ApplicationsConsumption of dietary fiber offers health benefits including lower risk for coronary heart diseases, diabetes and certain gastrointestinal diseases. The increased consumption of steamed bread enriched with pineapple peel fiber is proposed for health reasons. Pineapple is one of the important fruits, and its peel contained some phytochemicals such as fiber and polyphenol. The pineapple peel fiber was extracted and could be supplied as a potential source of dietary fiber. The study demonstrated fiber-enriched steamed bread with good sensory quality could be produced by the substitution of wheat flour by 5–10% pineapple peel fiber.
Despite the great variety of physicochemical and rheological tests available for measuring wheat flour, dough and gluten quality, the US wheat marketing system still relies primarily on wheat kernel hardness and growing season to categorize cultivars. To better understand and differentiate wheat cultivars of the same class, the tensile strength, and stress relaxation behavior of gluten from 15 wheat cultivars was measured and compared to other available physicochemical parameters, including but not limited to protein content, glutenin macropolymer content (GMP) and bread loaf volume. In addition, a novel gluten compression–relaxation (Gluten CORE) instrument was used to measure the degree of elastic recovery of gluten for 15 common US wheat cultivars. Gluten strength ranged from 0.04 to 0.43 N at 500% extension, while the degree of recovery ranged from 5 to 78%. Measuring gluten strength clearly differentiated cultivars within a wheat class; nonetheless it was not a good predictor of baking quality on its own in terms of bread volume. Gluten strength was highly correlated with mixograph mixing times (r = 0.879) and degree of recovery (r = 0.855), suggesting that dough development time was influenced by gluten strength and that the CORE instrument was a suitable alternative to tensile testing, since it is less time intensive and less laborious to use.
Cereal Chem. 81(2):207-219 The effect of moisture content on the linear viscoelastic properties of gliadin hydrated to 30 and 40% moisture content (gliadin(30%) and gli- adin(40%), respectively) was determined. These two moisture contents bracketed the equilibrium moisture content of gliadin, which was 37.6%. Time-temperature-superposition was used to develop master curves of the elastic modulus (G'), viscous modulus (G''), dynamic viscosity (η'), and tan δ (G''/G') from isothermal frequency sweep data obtained at 25-80°C. Smooth master curves were obtained for all of the viscoelastic functions for both gliadins. Gand G'' showed a power law dependency on frequency (with G'' > G') for frequencies
Dynamic measurements and retardation tests were combined to characterise the linear viscoelastic behaviour of wheat flour dough in the 10−5–102rad/s frequency range. Analysis of the data provided the Newtonian steady-state viscosity, the steady-state compliance, the terminal relaxation time, the viscoelastic plateau compliance and a measure of the upper frequency limit of the viscoelastic plateau. The influence of dough water content and composition of high molecular weight glutenin subunits on dough viscoelasticity was studied. Both factors affected dough viscoelasticity in a similar and remarkable way. In particular, the same inverse relationship between steady-state viscosity and compliance, and the same power law relationship between steady-state and plateau compliances, was found to hold whether the variability was due to high molecular weight glutenin subunits or to dough water content.
The aim of the present work has been to study the equibiaxial extensional deformation of glycerol plasticized moisture-containing gluten (MG) with different MG volume fractions ranging from 0.56 to 0.75 under lubricated squeezing flow at room temperature. The hyperelastic model with a strain energy potential of the Mooney–Rivlin form is applied to describe the biaxial stress as a function of biaxial strain at low strains. The initial shear modulus as a function of MG volume fraction reveals a particle network of gluten. Analysis of the relaxation modulus at biaxial strain 0.7 on the basis of the Kohlrausch–Williams–Watts (KWW) model reveals that decreasing volume fraction of MG increases the width of the distribution of relaxation times as well as the average relaxation time of wheat proteins.
This chapter discusses the gluten composition and properties. The chapter describes the basic information on the genetics, structure, and physics of gluten proteins. The different bakery applications of gluten, such as bread, biscuits/cookies, and pasta are discussed. The chapter also discusses the new area of non-food applications. Some examples describe how gluten functions are being used in new areas. Recommendations are given for future directions to further increase the use of this industrial protein. The chapter gives an overview of current-day gluten research, ranging from various food applications to more novel areas of non-food applications, where cereal science is less advanced. Cereals show a large variation in gluten properties, determined by both genetic and environmental factors. The cereal research has focused on unravelling these quality-function relations. The chapter discusses the problems of the definition of quality in a widely differing (product) context, and the complexity of the gluten protein network in relation to its physical behavior and its structure and composition.
Abstract
Since the 1980s, there have been general trends in the durum wheat milling industry to higher semolina extraction rate, and in the pasta processing industry to the use of higher drying temperatures. During this time, specification of gluten strength by gluten index, mixograph mixing properties and alveograph parameters has also become widespread. These trends prompted this study of the appropriateness of protocols for quality testing of Canadian durum wheat breeding lines. Four cultivars with intrinsic differences in yellow pigment levels and gluten strength were grown in field plots in Swift Current, Saskatchewan for three consecutive years. A laboratory-scale milling procedure was modified to produce semolina at extraction rates from about 65% to about 80%. Milling to extraction rates above 65%, the extraction rate used routinely in quality testing of Canadian durum wheat breeding lines, had a major impact on semolina ash content and colour, but did not offer any advantage in ranking cultivars for either semolina yield or semolina refinement. Gluten strength, as measured by gluten index, was independent of semolina extraction rate. Dough strength, as measured by mixograph properties and alveograph properties, showed a tendency to weakening at high extraction, particularly for strong cultivars. Semolina was processed into spaghetti using low-temperature (LT), high-temperature (HT) and ultra-high-temperature (UHT) drying cycles. The firmness of cooked spaghetti was predominantly influenced by protein content. As a result, cultivars generally ranked in spaghetti firmness according to protein content. Regardless of drying cycle or cultivar, spaghetti firmness increased as drying temperature increased. Spaghetti dried at LT was less yellow than spaghetti dried at HT or UHT, probably due to thermal inactivation of the bleaching enzyme lipoxygenase at HT and UHT. Regardless of drying cycle, spaghetti became duller, more red and less yellow as extraction rate increased. For each spaghetti trait, cultivar ranking remained relatively constant regardless of extraction rate or drying temperature. On the basis of these results, there appears to be no advantage to increasing semolina extraction rate beyond 65% for evaluation of durum wheat milling performance, gluten strength or pasta properties. In addition, it appears that one drying cycle is adequate to reliably evaluate durum wheat lines for spaghetti colour and firmness.
Durum wheat samples (three varieties), milled to yield straight-grade and patent flours, were processed into YANs. CWHWS and CWRS flours, customarily employed to make noodles, were included for comparative purposes. Uniaxial stress relaxation parameters, %SR, K1 and K2, derived from Peleg's model, were determined for all cooked noodles. Analysis of variance indicated a significant durum sample effect (P < 0.0001) on all three parameters. Significant differences (P = 0.05) were observed among all three CWHWS parameters and the durum flour samples, but not for CWRS. Significant correlations were detected among the three stress relaxation parameters and empirical texture measurements: RTC, REC and MCS. Flour yield exhibited a significant effect (P = 0.05) on %SR, K1 and K2, which was not detected using the empirical texture measurements. The uniaxial stress relaxation test provides a complementary, discriminating method for YAN texture measurement.
This describes the use of uniaxial compression to characterize and discriminate Asian noodle quality texture parameters on the basis of rheological principles. It demonstrates the discriminatory power of three parameters to discern similar noodle flour sources. The technique and parameters are simple to calculate and are well correlated with traditional empirical texture measurements.
Cereal Chem. 80(2):203–211 Field studies were conducted over three years at two locations in Saskatchewan, Canada, to determine the effect of nitrogen fertilizer on protein quantity and protein strength in 10 cultivars of durum wheat (Triticum turgidum L. var. durum) representing a range of gluten strength. Increasing nitrogen fertilizer resulted in increased protein content in all cultivars across environments. Cultivars were clearly differentiated on the basis of gluten strength using a gluten index (GI), SDS sedimentation (SDSS), alveograph indices of overpressure (P) and deformation energy (W), mixograph energy to peak (ETP), and mixograph bandwidth energy (BWE) at all fertilizer levels. Variable cultivar response to nitrogen fertilizer was observed only for protein content, GI, and alveograph W. The nature of the cultivar-by-fertilizer interaction for GI suggested that the conventional strength cultivars would benefit more from nitrogen fer-tilizer than the extra-strong types, which showed no change or slight decreases in GI with nitrogen fertilizer despite an increase in total gluten. SDSS increased with nitrogen fertilizer, following similar trends as protein. Gluten strength rankings of the cultivars by SDSS were main-tained with increased fertilizer. Fertilizer had little effect on alveograph P, mixograph ETP, and mixograph BWE. Overall, GI values were more stable across increasing levels of nitrogen fertilizer and resultant increased protein content compared with SDSS, mixograph development time, and alveograph W and L, suggesting it is a good test for estimating intrinsic gluten strength for cultivars with a wide range of protein content.
Cereal Chem. 70(2):122-126 Extruded noodles were prepared from durum wheat semolina of variable ness. The Instron peak force measurement was found to be a more precise protein content to provide a series of samples with a range of cooking indicator of noodle firmness than was peak energy. The rheometer was quality. Firmness of cooked extruded noodles was measured using an able to differentiate between samples and to rank the noodle samples Instron Universal Testing Machine and compared with the storage in the same order as the Instron did. Although moisture content was modulus and dynamic viscosity obtained by dynamic rheometry. A strong shown to have a major influence on the texture of cooked noodles, the correlation (r 2 at least 0.87) was found between the Instron values and differences in moisture between samples were not sufficient to produce the rheometer measurements at both optimum and overcooking times, the differences measured by either the Instron or by dynamic rheometry. indicating the sensitivity of dynamic rheometry to changes in pasta firm-It is generally accepted that texture is the main criterion for assessing overall quality of cooked pasta. Proper evaluation of pasta cooking quality requires consideration of a number of factors including elasticity, firmness, surface stickiness, cooking tolerance, water absorption, and loss of solids to cooking water (Manser 1981). Taste panels can be used to estimate pasta cooking quality (Menger 1979), but they are time-consuming and im-practical when sample size is limited or large numbers of samples are to be evaluated. In response to these constraints, a number of instrumental methods have been developed that successfully estimate cooked pasta texture parameters (Matsuo and Irvine 1969, 1971; Walsh 1971; Voisey and Larmond 1973; Feillet et al 1977; Voisey et al 1978). Furthermore, a chemical test was developed by D'Egidio and co-workers (1982) that related sensory evaluation of spaghetti glueyness, bulkiness, and firmness to the amount of total organic matter rinsed from the surface of cooked spaghetti. The use of the Instron Universal Testing Machine (Instron, Canton, MA) is well established for the measurement of pasta firmness (Walsh 1971, Oh et al 1983). It is the instrument recom-mended by AACC (1983) in approved method 16-50. Like most instrumental tests used to evaluate pasta quality, it involves large deformation measurements on the samples tested. There has been growing interest in the use of dynamic mechani-cal tests employing controlled strain and stress to study the funda-mental rheological properties of dough (Navickis et al 1982, Abdelrahman and Spies 1986, Dreese et al 1988). These methods are applicable to polymeric materials, such as cooked pasta, dis-playing viscoelastic behavior. Therefore, it seemed reasonable to use dynamic rheometry to study the viscoelastic properties of cooked pasta and to determine the relationship with Instron firm-ness values.
Cereal Chem. 74(6):781–785 Thirteen hard red spring wheat genotypes in which seven genotypes had the same high molecular weight (HMW) glutenin subunits (2*, 7+9, 5+10) were compared for their physical-chemical and breadmaking prop-erties. These samples were categorized into three groups based on their dough mixing and baking performances as follows: the strong dough (SD) group (six genotypes), characterized by the strongest dough mixing (average stability, 35 min); the good loaf (GL) group (four genotypes), characterized by the largest loaf volume; and the poor loaf (PL) group (three genotypes), characterized by the smallest loaf volume. Total flour proteins were fractionated into 0.5M salt-soluble proteins, 2% SDS-soluble proteins, and residue proteins (insoluble in SDS buffer). SDS-soluble proteins, residue proteins, and total flour proteins were analyzed by SDS-PAGE and densitometry procedures to determine the proportions of HMW glutenin subunits, medium molecular weight proteins, and low molecular weight proteins in relation to the total amount of proteins. No differences in the amount of salt-soluble proteins were found among the different groups of samples. Solubilities of gluten proteins (total proteins minus salt-soluble proteins) in SDS buffer were related to the differences in dough strength and baking quality among the three groups. The SD group had the lowest solubility and the PL group had the highest. SDS-PAGE analysis showed that SDS-soluble proteins of the SD group contained a smaller amount of HMW glutenin subunits than those of the GL and PL groups. The highest proportions of HMW glutenin subunits in total flour proteins were found in the SD group, while the PL group had the lowest percentage of HMW glutenin subunits in their total flour proteins. These results showed that the total quantities of HMW glutenin subunits played an important role in determining the dough mixing strength and breadmaking performance of hard red spring wheats.
Cereal Chem. 76(5):638–645 Durum wheat gluten strength is important in determining extrusion properties and pasta cooking quality. Durum wheats varying in strength were tested using an alveograph and a 2-g micro-mixograph, both widely accepted techniques for determination of physical dough properties. Doughs from the 2-g micro-mixograph were characterized by dynamic oscillatory and large deformation creep tests using a controlled stress rheometer. Mechanical properties obtained from both testing regimes were strongly correlated with many of the parameters provided by the alveo-graph and micro-mixograph. Maximum strain attained after 5 min creep ranged from <5% for the strongest least extensible cultivar to >25% for the weakest cultivar, with a coefficient of variation among replicates of <10%. Storage modulus (G′) at 2 Hz ranged from ≈7,000 Pa for the weakest cultivar to >16,000 Pa for the strongest, least extensible cultivars, with a coefficient of variation of <6%. Tan δ (G′′/G′) values were ≈0.4 for the strongest versus >0.5 for the weakest cultivars, indicating the larger contribution of the elastic component in the strong cultivars. The rheometer allows discrimination of durum wheat cultivars of varying gluten strength while requiring less sample than traditional physical dough testing tech-niques.
As was mentioned in chapter 10, end-linking reactions can be used to make networks of known structures, including those having unusual chain-length distributions. One of the uses of networks having a bimodal distribution is to clarify the dependence of ultimate properties on non-Gaussian effects arising from limited-chain extensibility, as was already pointed out. The following chapter provides more detail on this application, and others. In fact, the effect of network chain-length distribution, is one aspect of rubberlike elasticity that has not been studied very much until recently, because of two primary reasons. On the experimental side, the cross-linking techniques traditionally used to prepare the network structures required for rubberlike elasticity have been random, uncontrolled processes, as was mentioned in chapter 10. Examples are vulcanization (addition of sulfur), peroxide thermolysis (free-radical couplings), and high-energy radiation (free-radical and ionic reactions). All of these techniques are random in the sense that the number of cross-links thus introduced is not known directly, and two units close together in space are joined irrespective of their locations along the chain trajectories. The resulting network chain-length distribution is unimodal and probably very broad. On the theoretical side, it has turned out to be convenient, and even necessary, to assume a distribution of chain lengths that is not only unimodal, but monodisperse! There are a number of reasons for developing techniques to determine or, even better, control network chain-length distributions. One is to check the “weakest link” theory for elastomer rupture, which states that a typical elastomeric network consists of chains with a broad distribution of lengths, and that the shortest of these chains are the “culprits” in causing rupture. This is attributed to the very limited extensibility associated with their shortness that is thought to cause them to break at relatively small deformations and then act as rupture nuclei. Another reason is to determine whether control of chain-length distribution can be used to maximize the ultimate properties of an elastomer. As was described in chapter 10, a variety of model networks can be prepared using the new synthetic techniques that closely control the placements of crosslinks in a network structure.
Chapter 2 dealt with the response to step, slope, and harmonic excitations. These are the stimuli used most often to elicit responses for the purpose of characterizing linear viscoelastic behavior. They were, therefore, called standard excitations. They share the common feature of being simple stimuli, applied once only, at t = 0. Viscoelastic response may be elicited, however, by a variety of other stimuli which we shall discuss, as a matter of convenience, under the heading of non-standard excitations. They fall naturally into two groups:
(1)
the response to the removal or the reversal of direction of a stimulus, and
(2)
the response to repeated stimuli.
This chapter discusses the physicochemical properties of wheat proteins in relation to functionality. One of the major obstacles to the characterization of wheat proteins has been the lack of methods to solubilize the total protein. On the basis of chemical composition, there are two broad classes of proteins in wheat—the albumidglobulins and the gliadidglutenin, or gluten, proteins. Whereas albumin or globulin proteins are readily soluble in aqueous solution, the gluten proteins present problems for their solubilization. Several methods have been applied for studying the surface hydrophobicities of wheat proteins. These include hydrophobic interaction chromatography (HIC), reversed-phase high-performance liquid chromatography (RP-HPLC), and methods involving interactions with apolar ligands in solution. The solubility of proteins is hindered by hydrophobic effects resulting from the high content of nonpolar side chains. This effect is usually minimized by folding of molecules so as to bury a large proportion of the nonpolar side chains in the interior of the molecule, where they are shielded from interaction with water molecules.
This paper serves as a review of work performed in the author’s and his collaborators’ laboratories over the last 15 years on the general topic of structure/property relationships for biopolymer (including food biopolymer)solutions and gels. In the first part, we describe how small deformation oscillatory measurements have enabled a distinction to be made between ‘‘entanglement networks,’’ ‘‘strong’’ and ‘‘weak’’ gels used, respectively, as food thickeners, gels, and stabilizers. At small enough strains both strong and weak gel systems give essentially the same mechanical spectrum, with G′≳G″, and with both moduli largely independent of frequency. However, the deformation dependence of these two classes of materials is very different. At large deformations strong gels will rupture and fail, while weak gels flow without fracture and but show recovery of solid (gel‐like) character. In this paper the various classes of food biopolymers are described, and their rheological properties related to differences in structure. The final part contrasts the behavior of a weak gel (xanthan gum) and entanglement solution (guar gum). This distinction is confirmed by their respective responses in start shear experiments. Guar solutions behave much like most other polymer solutions, whereas xanthan solutions show a very pronounced overshoot peak at low strains, and very long peak overshoot recovery times.
Twenty-seven durum wheat genotypes originating from different geographical areas, all expressing LMW-2 at Glu-B3, and five bread wheats were evaluated for flour mixing properties, dough physical characteristics. and baking performance. Gluten polymeric composition was studied using size-exclusion HPLC of unreduced flour protein extracts. As a group, durum wheats had poorer baking quality than bread wheats in spite of higher protein and total polymer concentrations. Durum wheats exhibited weaker gluten characteristics, which could generally be attributed to a reduced proportion of SDS-unextractable polymer, and produced less extensible doughs than did bread wheats. However, substantial variation in breadmaking quality attributes was observed among durum genotypes.
The relaxation properties of flour-water-salt doughs prepared from four different flour types (weak medium, strong, and extra strong) at different water absorption levels from 58 to 66% with protein contents of 10.0, 10.9, 13.2, and 11.8%, respectively, were studied by imposing varying strain amplitudes of 0.1-29%. Oscillatory tests in the linear viscoelastic region of the 66% absorption strong and weak dough cannot distinguish between the two types of dough. The inability to differentiate between dough types also applied to oscillatory tests on 58% absorption weak and 66% absorption strong doughs. However, the relaxation modulus of dough (extending over time) behaved quite distinctively at high strains, where dough samples experience large deformations. At strain amplitudes of less than or equal to 0.1% (i.e., in the linear viscoelastic region), different dough types behaved similarly. Likewise, the relaxation modulus completely relaxed at sufficiently long times. The magnitude of the modulus at intermediate- and high-strain amplitudes were in the order: extra strong > strong > medium > weak, indicating a higher level of elasticity in the extra strong dough samples despite its lower protein content. The relaxation times spectrum of the weak flour, extracted from the relaxation modulus data, reveals a broad relaxation process. The stress relaxation data are very reproducible at high-strain amplitudes (approximate to 1-15% for up to 3 x 10(3) sec). This work demonstrated, for the first time, the consistency in oscillatory and relaxation measurements for dough. It also clearly showed that linear viscoelastic data, although important in the characterization of time scales in dough, are largely irrelevant in differentiating between dough types. Furthermore, without proper care, a false steady-state behavior can be obtained with standard viscometric measurements due to slippage at the dough-plate interface.
Measurement of the linear viscoelastic properties is the basic rheological characterization of polymer melts. These properties may be evaluated in the time domain (mainly creep and relaxation experiments) or in the frequency domain. This chapter talks about mechanical spectroscopy, where the sample experiences a harmonic stimulus (either stress or strain). The linear viscoelastic data may be used as a pure rheological characterization, and the viscoelastic parameters may be related to some processing or final properties of the material under study. Moreover, linear viscoelasticity and nonlinear viscoelasticity are not different fields that would be disconnected: in most cases, a linear viscoelastic function (relaxation function, memory function or distribution of relaxation times) is used as the kernel of non linear constitutive equations, either of the differential or integral form. That means that if one could define a general nonlinear constitutive equation that would work for all flexible chains, the knowledge of a single linear viscoelastic function would lead to all rheological properties.
The gliadin proteins of seven durum wheat varieties of diverse origins were analysed by two different two-dimensional electrophoresis techniques. Three of the varieties and biotype A of Duramba, all known to have good pasta cooking qualities, were confirmed to contain a γ-gliadin, usually referred to as band 45, and ω-gliadin band 35. All of these wheats were also shown to contain the same group of low molecular weight (LMW) subunits of glutenin, termed LMW-2. This suggests that genes coding for γ-gliadin 45 and ω-gliadin 35, known to be linked tightly to each other on the short arm of chromosome 1B, are also linked tightly to genes for LMW-2. In similar studies, three other varieties and biotype D of Duramba, all of poor pasta cooking quality, were shown to contain γy-gliadin 42, ω-gliadins 33, 35 and 38 and LMW glutenin subunits, LMW-1. The results are discussed in relation to the identification of those proteins that cause the association between the presence of γ-gliadin 45 and strong gluten in durum wheat varieties.
The importance of glutenin in bread-making quality has led to a substantial research effort. Studies on glutenin can be grouped into four categories: studies that determine the statistical relationships between the quantity of fractions and quality, studies of reconstitution and fortification, breeding and genetic modification, and those that assess structure–function relationships during processing. Statistical relationships between glutenin, glutenin fractions and glutenin polypeptides and quality have been established. The SDS or acetic acid unextractable glutenin correlated strongly with quality parameters. For highMrglutenin subunits the relationships with quality are less strong. In some studies it was demonstrated that the presence of some highMrglutenin subunits is correlated with the quantity of unextractable glutenin. Therefore, subunits are probably indirectly linked with bread-making qualityviathe quantity of unextractable glutenin. Recombination and fortification studies are hampered by changes in functionality of proteins after their separation. Recently, small scale tests have been developed in which small amounts of glutenin fractions can be studied. Controlled breeding studies have demonstrated the importance of highMrglutenin subunits 5+10 and, to a lesser extent, 1 or 2* for quality. In most of these studies the quantity of unextractable glutenin is not reported. This hampers adequate conclusions on cause–effect relationships. During dough processing large changes occur in the extractability of glutenin. The significance of these changes for dough properties and bread quality still requires investigation.
The mixing characteristics and bread-making qualities of flours, reconstituted flours and glutens from a diverse range of wheat cultivars obtained from Canada, France and the UK, were investigated. Simple correlations were calcu-lated among Mixograph parameters, loaf volume, Glu-1quality scores, protein content, SDS-sedimentation volume and baking absorption. The results indicate that the mixing properties of flours from cultivars in the medium–strong range are significantly influenced by their protein contents. On the other hand, the mixing properties of ‘extra strong’ or weak flours are relatively less affected by their protein contents, and it appears that the protein quality primarily controls their behaviour during mixing. Gluten samples, other than weak glutens from cvs Riband and Corin, required a longer time to mix to peak dough resistance (PDR) than their corresponding flour or reconstituted flour samples. However, the differences in mixing time were more pronounced between ‘extra strong’ glutens and their corresponding flours or reconstituted flours. The Mixograph parameter PDR showed highly significant (P
The initial value problem is solved for the transient network model of physically crosslinked gels. Stress relaxation following a sudden macrodeformation is calculated for several realistic models of the chain breakage rate β(r). It is shown that, on large time scales, stress decay obeys a power law when β(r) has significant r-dependence, the precise value of the power being dependent on the high stretching behaviour of β(r). For instance, the shear stress decays as ≈t if β(r) is proportional to rn at high stretching. Although the Lodge-Meissner relation still holds, time-strain separability loses its physical background. Overshoot phenomena in shear and normal stress, which appear after steady flows are started at the initial equilibrium state, are also analyzed. It is found that the shear stress first shows a transient maximum, and then maxima of the first and second normal stress differences follow. Larger overshoot is expected for larger values of the shear rate γ, but the time at which the stress reaches its maximum is almost independent of γ The elongational stress is also obtained as a function of time.
The effect of proteolytic enzymes, associated with Fusarium head blight, on wheat storage proteins and dough functionality was studied. Fusarium damaged kernels (FDK) and sound kernels were hand-picked from F. graminearum Schwabe and F. avenaceum (Fr.) Sacc. infected samples of bread and durum wheat. Scanning electron microscopy revealed significant degradation of endosperm protein in FDK. Storage proteins from FDK and sound kernels were analyzed by SDS-PAGE, RP-HPLC, and SEHPLC. Total storage protein was lower in FDK but no significant qualitative differences in protein were detected by either RP-HPLC or SDS-PAGE. SE-HPLC was used to follow the hydrolysis of wheat storage protein by proteolytic enzymes found in FDK and a pure culture of F. graminearum. Selective inhibition of proteolytic activity by p- chloromercuribenzoate, and not soybean trypsin inhibitor or iodoacetic acid, suggests that the F. graminearum protease is an alkaline protease. Farinograph and extensigraph curves showed that the presence of FDK decreased dough consistency and resistance to extension. The presence of FDK in flour resulted in a substantial reduction in loaf volume. The loss of dough functionality and loaf volume potential was attributed to the presence of fungal proteases.
Measurements of shear stress relaxation of wheat flour dough and its corresponding gluten in cone-plate geometry are reported. The range of shear strains used is 0.1–1.0. It is found that the relaxation function is separable into a function of strain and a function of time for shear strains up to 0.4 for dough and 1.0 for gluten. The strain function is non-linear for both dough and gluten. Typically the observed half relaxation time is 1.5 seconds for both dough and gluten. The data suggest the existence of two separate flow processes. The observed time-dependence of the relaxation function has been analysed in terms of a theory of flow as a cooperative phenomenon. In this analysis the process which occurs at short times (0.1–10 s), is characterized by a four-fold coordination of flow units. This process is similar in dough and gluten. The second process, occurring at longer times (10–104 s), is different for dough and gluten and the coordination numbers found are two and one, respectively. This second flow process has to our knowledge not been reported previously.
The viscoelastic behavior of semidilute solutions of metal-neutralized sulfonated EPDM polymers in a paraffinic oil is described. The results are compared to those of the base EPDM solutions. The data of the bulk behavior of these two polymer systems as well as those of another comparable molecular weight polyisobutylene polymer are also described for comparative purposes. The detailed solution studies of zinc-neutralized sulfonated EPDM polymers demonstrate the changes in the permanence and strength of physical associations as a function of diluent concentration. At 5 wt % zinc sulfo-EPDM, the behavior of this solution at high frequencies resembles that of a covalently cross-linked elastomer, while at low frequencies the behavior is that of a typical Newtonian fluid. In contrast, the base EPDM dissolved at 5 wt % concentration displays virtually no indication of entanglements. A range of polymer concentrations of zinc sulfo-EPDM was investigated from 1 to 12.5 wt % polymer at a sulfonate level of 20 mequiv/100 g of polymer. At polymer concentrations near 1 wt %, a slight entanglement plateau was evident. Similar studies were conducted on polymers having a range of sulfonate levels of 10, 20, and 30 mequiv/100 g, all at 5 wt % polymer concentrations. As sulfonation level increases, the entanglement plateau is extended and the modulus increases. These findings are consistent with a dynamic interaction of metal sulfonate groups whose degree of clustering is widely variable in nonpolar media. These results contrast markedly with those of the magnesium sulfonated EPDM which, under comparable conditions, exhibits a much more persistent network. The viscoelastic data are analyzed following conventional linear viscoelastic theories. Monomeric friction coefficients of various systems are calculated with the modified Rouse model, and relationships of viscoelastic parameters, the entanglement plateau GN0, recoverable compliance Je0, and zero-shear viscosity, η0, as a function of concentration are established for the zinc salt solution of sulfo-EPDM. The following relations for the sulfonated EPDM were obtained: GN0 ∝ C2.5, Je0 ∝ C-1, and η ∝ C6.0, and for the unsulfonated EPDM polymer GN0 ∝ C2.0, Je0 ∝ C-1, and η ∝ C1.7 and η ∝ C4.5 below and above the breakpoint. In summary, these studies demonstrate how metal sulfonate interactions alter the solution behavior of this class of ionomers as a function of polymer concentration, sulfonate level, and cation type and explain how some ionomers simply behave as higher molecular weight analogues of EPDM, while others can act as if they were highly cross-linked systems simply by changes in the cation or sulfonate level.
A simple model is introduced to describe the dynamics of physically cross-linked networks in which junctions are sufficiently weak to break and recombine in thermal fluctuations. The time-evolution equation under arbitrary macrodeformation is derived for the creation and annihilation of the junctions - and hence for the number of elastically effective polymer chains with a fixed end-to-end vector. We focus our attention specifically on the unentangled networks in which the molecular weight Mx between neighboring junctions is smaller than the entanglement molecular weight Me, so that each chain obeys Rouse dynamics modified by sticky trapping centers rather than reptation. Stress-strain relation under shear and elongational deformation is detailed for a model network which is made up of polymers of uniform length with associating functional groups at their chain ends. On longer time scales than the junction breakage time, the total number of effective chains decreases with time - resulting in an intranetwork flow.
We present a model for dynamics of entangled networks made up of linear chains with many temporary cross-links. At times shorter than the lifetime of a cross-link such networks behave as elastic rubbers (gels). On longer time scales the successive breaking of only a few cross-links allows the chain to diffuse along its confining tube. The motion of a chain in this hindered reptation model is controlled by the concentration and lifetime of tie points. We calculate the self-diffusion coefficient and discuss the stress relaxation in terms of molecular parameters, including the chain length, the number of cross-linking groups per chain, and the lifetime and probability of formation of cross-links. We find good agreement with recent experiments by Stadler et al. on model thermoplastic elastomers.
Cereal Chem. 76(4):582–586 Data on the quality of durum wheat genotypes grown under eight environments (site-year combinations) were evaluated to determine the relative effects of genotype and environment on quality characteristics associated with gluten strength, protein content, and pasta texture. The 10 durum wheat genotypes assessed in this study represented a range of gluten strength types from the very strong U.S. desert durum genotype, Durex, to the medium strength Canadian genotype, Plenty. Considerable genetic variability was detected for all quality characteristics studied. Geno-type-environment interaction was significant for all quality parameters evaluated, with the exception of mixograph development time. Genotype-environment interaction was most important in determining protein con-tent and least important in determining gluten index, gluten viscoelasticity, and SDS sedimentation volume. The nature of the genotype-environment interaction was evaluated by determining the number of significant cross-over (rank change) interactions. There was at least one significant crossover interaction between pairs of genotypes and environments for five of eight quality traits tested. Of 45 genotype pairs, eight and six showed sig-nificant crossover interactions for protein content and pasta disk visco-elasticity, respectively. Significant crossover interactions were at least partially due to the differential response of Canadian genotypes as compared with U.S. genotypes. With the exception of protein content and pasta disk viscoelasticity, our results suggest that among the selected sample of 10 genotypes, genotype-environment interactions were minor and due primarily to changes in magnitude rather than changes in rank.
The B low-molecular-weight (LMW) glutenin subunit composition of a collection of 88 durum wheat cultivars was analyzed. Extensive
variation has been found and 18 different patterns were detected. Each cultivar exhibited 4–8 subunits, and altogether 20
subunits of different mobility were identified. The genetic control of all these subunits was determined through the analysis
of nine F2 populations and one backcross. Five subunits were controlled at the Glu-A3 locus, 14 at Glu-B3 and 1 at Glu-B2. At the Glu-A3 locus each cultivar possessed from zero to three bands and eight alleles were identified. At the Glu-B3 locus each cultivar showed four or five bands and nine alleles were detected. Only one band was encoded by the Glu-B2 locus. A nomenclature for these alleles is proposed and the relationship between them and the commonly used LMW-model nomenclature
is discussed.
Seven methods (Voigt model, Maxwell model, operator equation, mechanical impedance function, creep curve, relaxation curve, and dynamic modulus function) of specifying viscoelastic behavior are discussed. A number of exact relations between these methods of specification are worked out in detail. The majority of these relations are simple enough to be of practical value although a few are too cumbersome. Approximate relationships between the creep curve, the relaxation curve, Maxwell model, and Voigt model are discussed; and numerical examples show the magnitude of errors introduced by the approximation to be small even in quite unfavorable cases. A consideration of the practical utility and physical meaning of the various methods of specification distinguishes between (1) those of general descriptive value and those of direct experimental value; (2) those useful in a phenomenological study of mechanical behavior and those more suited to a formulation of molecular theory. A summary of the present molecular theories is presented together with their interpretation in terms of the Voigt and Maxwell specifications.
The effect of temperature, rest period, and water content on stress relaxation in doughs held at constant extension has been studied with a relaxometer previously described. Temperature was varied from 13 to 35°C, rest period from 2 to 120 min, and water content from 74.4 percent to 86.0 percent dry basis. It is found that the shape of the relaxation curves on a log time plot does not change with temperature in the above range but that the curve is shifted laterally along the log time axis. This permits the construction of master curves valid in the temperature range and extends the time scale of observation. The long relaxation time end of the distribution of relaxation times is affected most by rest period, decreasing as rest period is increased, and the short time end increases as water content is decreased. Activation energies from 11 to 24 kcal per mole are calculated for relaxation from the shift of the curve on the log time axis. There is an indication that the activation energy depends on temperature and increases with rest period.
A mathematical framework, based on the general Maxwell model, is discussed and the distribution function on the log time axis is interpreted in terms of viscosity and modulus of the relaxing mechanisms. Special reference is made to the ``box distribution'' and a viscosity is calculated.
Samples of no. 1 and no. 2 Canada Western Amber Durum wheat from two consecutive Canadian Grain Commission harvest surveys were composited according to protein content. The resulting composites were milled to achieve three levels of starch damage. When the standard ICC Alveograph test at constant water addition was performed, the curves became higher and shorter as starch damage increased, owing to the increasing flour water absorption. When alveograph water addition was adjusted, the shape of the Alveograms was almost independent of starch damage. As protein content increased, Alveograph extensibility (length) increased. Starch damage was the predominant factor influencing Farinograph water absorption, development time and stability. Protein content exerted a moderate influence on Farinograph absorption. At low protein content, Farinograph development time and stability decreased as starch damage increased. Depending on protein content, starch damage and baking procedure, durum wheat loaf volume was 65 to 85% of that achieved for a high-quality Canadian bread wheat of comparable protein content. Remix-to-peak baking (long bulk fermentation) performance was influenced positively by protein content and was influenced negatively by starch damage. When baked by the Canadian short process (no bulk fermentation), the negative effects of starch damage on baking performance were not apparent. Bread-crumb properties of all Canadian short-process breads were much better than the corresponding remix-to-peak breads, approaching those of high-quality Canadian bread wheats. When potassium bromate was eliminated from the Canadian short process formula (which includes 37·5 ppm ascorbic acid), no negative effects on bread quality were apparent.
The rheological characteristics of wheat flour doughs from the cultivars Obelisk and Katepwa and of biscuit flour doughs, and also of biscuit flour doughs containing glutens isolated from cv. Obelisk and cv. Katepwa flour, were compared and discussed in relation to bread making performance. Four different rheological methods were employed: two fundamental methods, i.e. dynamic (oscillatory) and uniaxial compression tests, and two empirical methods, i.e. tests using a Brabender Extensograph and a Chopin Alveograph. The fundamental methods showed that a dough of cv. Katepwa flour had a higher resistance to deformation and was more elastic than a dough of cv. Obelisk flour. Doughs of biscuit flour exhibited an intermediate behaviour, except that loss tangent values were close to those of a cv. Obelisk flour dough. Addition of cv. Obelisk gluten to biscuit flour hardly affected the rheological behaviour, whereas addition of cv. Katepwa gluten resulted in a higher resolution resistance to deformation and a higher elasticity. Uniaxial compression tests clearly showed the strain hardening and strain rate thinning characteristics of the flour doughs, which were most pronounced for a dough of cv. Katepwa flour. The rheological characteristics of cv. Obelisk and cv. Katepwa flour doughs and of biscuit flour doughs containing the glutens corresponded with those of the isolated hydrated glutens. The information about the rheological behaviour of the flour doughs obtained by the four methods was complementary and in good agreement, despite differences in applied strains, deformation rates and modes of deformation. The empirical tests showed that the extensibility of the biscuit flour dough was less compared to that of the other doughs. This study suggests that in order to obtain a high loaf volume and a fine crumb structure, wheat flour dough has to exhibit biaxial strain hardening and extensibility exceeding a minimum level; it is likely that the resistance to deformation may vary within a certain range.
Mixing characteristics, descriptive rheological measurements, and stress relaxation behaviour of flour–water doughs from a diverse range of Canadian hard common wheat cultivars were investigated. When mixed in a mixograph, flours from two varieties and two breeding lines in the Canada Western Extra Strong (ES) breeding trials required longer time (6–8 min) and higher work input (270–350 Arbitrary Units) to mix to peak dough resistance (PDR) than moderately strong to strong bread wheats (MS) (2·5 min and 110–120 AU). Extensigraph maximum resistance to extension (Rmax/E ratio) and alveograph P/L (tenacity to length ratio) values were higher for doughs from ES cultivars than for MS cultivars. Flour-water doughs from ES cultivars exhibited higher G′ andG′′ , and lower tan δ values than those from MS cultivars at all frequencies. Doughs from ES cultivars exhibited slower relaxation rates than exhibited by MS. Doughs from ES cultivars exhibited characteristic bimodal relaxation spectra, which appeared to represent two discrete spectra separated by time. In contrast, doughs from MS cultivars exhibited only one prominent peak at about 0·1 s, with the second peak reduced to a shoulder. Adding cysteine (30 ppm) to flour–water mixtures of two ES cultivars reduced mixograph mixing times to 2·5 min. The ES doughs with added cysteine exhibited relaxation behaviour similar to that of MS doughs without added cysteine. This suggests that high molecular weight glutenins are primarily responsible for the longer mixing times of ES cultivars, and the characteristic second peak in their relaxation spectra. Relaxation behaviour of all doughs examined was positively correlated with mixograph mixing time, extensigraph Rmax/E, alveograph P/L, and mixing energy and mixing time obtained by a long and a short bread-making process. However, the stress relaxation data demonstrated no simple correlation to loaf volume, because all of the cultivars had sufficient strength to produce high quality bread when dough was optimally developed. The stress relaxation measurements differentiated between overly strong (ES) cultivars, and cultivars that have mixing requirements that are more suitable for overall bread-making performance (MS). Stress relaxation results also appeared to reflect expected qualitative differences in the underlying molecular weight distribution of glutenin polymers which relate to dough strength.
The LECO FP-228 "Nitrogen Determinator" was compared with the AOAC copper catalyst Kjeldahl method, 7.033-7.037, for the determination of crude protein in feed materials. The completely microprocessor-controlled instrument determines nitrogen by measuring the nitrogen gas following combustion of the sample; it was easy to operate and broadly applicable. A wide variety of feed materials of various nitrogen levels were analyzed in one mixed sequence. Results were precise, accurate, and rapid. Analysis time for one sample was approximately 3 min. Fourteen samples containing 2.5-15.5% N were selected for study and consisted of meals, grains, forages, and standard organic materials. The overall mean for the 14 samples by the LECO combustion method was 8.61% N compared with an overall mean of 8.58% N for the AOAC Kjeldahl method. Within-sample standard deviations for the LECO combustion method ranged from 0.013 to 0.052% N with a pooled standard deviation (SD) of 0.033% N for the 14 samples. Standard deviations for the AOAC Kjeldahl method ranged from 0.006 to 0.035% N with a pooled SD of 0.022% N. Combined average recovery of nitrogen from tryptophan, lysine-HCl, and EDTA determined by the LECO combustion method was 99.94% compared to 99.88% determined by the AOAC Kjeldahl method.
Using an improved method of gel electrophoresis, many hitherto unknown
proteins have been found in bacteriophage T4 and some of these have been
identified with specific gene products. Four major components of the
head are cleaved during the process of assembly, apparently after the
precursor proteins have assembled into some large intermediate
structure.
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