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Effect of cross-linked acetylated starch content on the structure and stability of set yoghurt
Abstract
In this research, the effect of cross-linked acetylated starch on the set yoghurt system was studied by investigating the flowability, viscoelasticity, zeta potential, conductivity and microstructure of the set yogurt system. The results indicated that the stability, elastic modulus (G′) and viscous modulus (G″) of the set yogurt system increased as the concentrations of cross-linked acetylated starch increased. The set yogurt system, which added the cross-linked acetylated starch, exhibited shear-thinning behavior and belonged to yield pseudoplastic fluid. The SEM micrographs demonstrated that the microstructures of set yoghurt were mainly composed by the network of casein. By adding cross-linked acetylated starch, the network of casein was strengthened, and both conductivity of the yoghurt system and particle size of casein micelles due to absorption of modified starch revealed the aggrandizement trend. It can be deduced that the starch adsorbs onto the surface of the casein micelle and this phenomenon prevents flocculation of the casein micelles owing to electrostatic adhesion, steric stabilization and osmotic effect.
... The steady state shear scanning ranged from 0.1 s −1 to 100 s −1 . Besides, the elastic modulus (G ) and viscous modulus (G ) were measured with fixed 0.1% strain, and frequency scanning ranged from 0.1-10 Hz in the dynamic rheological test [27,28]. The power law model is well-known for its extensively utilization in describing the flow properties of non-Newtonian liquids. ...
... All the fermented set yoghurts showed shear-thinning behavior and pseudoplasticity phenomenon, which corresponds to the results of Xu et al. [22] about the apparent viscosity of set yoghurts added with okra polysaccharides. Based on the report of Cui et al. [28], yoghurt shows the characteristics of pseudoplastic phenomenon and shear-thinning behavior mainly related to the breakage of bonds between protein aggregation, which is conducive to comparing the differences of rheological properties between different yoghurt samples. Compared with the control, when the concentration of added SA, GG, and KGM was 0.005%, the apparent viscosity of the set yoghurts presented little increase in different degrees, which was related to the bridging effect of polysaccharide under low concentration. ...
... In the frequency range of 0.1-10 Hz, the elastic modulus (G ), and viscous modulus (G") of all set yoghurts presented an upward tendency, and the logarithm of G was always higher than G", indicating that all set yoghurts had good elasticity and gel structure. The larger the elastic modulus value, the stronger the interaction between particles and the more stable the network structure [28]. It is obvious that as the concentration of SA, GG, or KGM addition increased, an increase in the G and G" of the set yoghurts was observed, which corresponded to the apparent viscosity as well (Figure 2). ...
The study investigated the preparation of set yoghurts by adding three common commercial polysaccharide stabilizers, namely sodium alginate (SA), gellan gum (GG), and konjac gum (KGM), in milk fermentation to evaluate their effects on the texture, rheology, and microstructure of set yoghurts. The physicochemical properties, water-holding capacity (WHC), texture, low-field nuclear magnetic resonance (LF-NMR), rheology, and microstructure of set yoghurts added with different kinds and quantities of polysaccharides were compared and analyzed. The results showed that the set yoghurts added with anionic polysaccharide GG had more obvious effects on improving WHC, firmness, and rheological properties compared with the set yoghurt added with KGM and SA. The firmness of set yoghurts with 0.02% (w/v) GG increased from 1.17 N to 1.32 N, which significantly improved the gel structure. The transverse relaxation time (T2) of set yoghurts added with GG was the closest to that of the control. Compared with the set yoghurts added with 0.02% SA and KGM, the free water area (A23) of the one added with 0.02% GG decreased most significantly. Moreover, all samples showed shear-thinning behavior, and the apparent elastic and viscous modulus (G', G″) increased with the increase of GG concentration. The G' and G″ of set yoghurts with 0.005% SA and KGM were higher than those in the control, decreased when adding 0.010%, and then increased with the increase of SA and KGM. Additionally, the microscopic observation demonstrated that the addition of GG in set yoghurts significantly promoted the formation of larger protein clusters and showed a tighter and more uniform protein network comparing with the other two polysaccharides (SA, KGM).
... Firstly, 1% hydrogels of all xanthan samples produced from six different carbon sources were prepared and kept at 25 • C for 24 h. After that, the rheology of xanthan samples was determined and studied as per the method stated in previous studies [40,42]. A controlled rheometer (with 2 mm gap of coaxial-cylinders fixture) was used in this study. ...
... For determining the flow characteristics of xanthan samples, viscosity and shear stress values at increasing shear rates (1 to 100 s − 1 ) were recorded. Finally, the obtained data was fitted to the Herschel-Bulkley model [40,42]. ...
... Carbon source n ± SD K ± SD (Pa. s n ) ʈ 0 ± SD (Pa) [40,42]. Similarly, the H-B model was also used in this work to model the shear stress data of xanthan samples obtained from different carbon sources at increasing shear rate. ...
The present study emphasizes improving the overall yield, productivity and quality of xanthan by Xanthomonas campestris using different carbon sources via optimizing the fermentation media and kinetic modelling work. After optimization, six carbon sources and one nitrogen source were selected for xanthan production in 5 L bioreactor. Kinetic modelling was applied to assess the experimental fermentation data and to check its influence on scale-up production. In this work, xanthan production reached 40.65 g/L with a growth-associated rate constant (α) of 2.831, and highest specific growth rate (μm) of 0.37/h while using maltose as the sole carbon source. Furthermore, rheological properties were determined, and Herschel-Bulkley model was employed to assess the experimental data. Interestingly, xanthan obtained from sucrose and glucose showed the highest yield stress (τ0) of 12.50 ± 0.31 and 7.17 ± 0.21. Moreover, the highest xanthan molecular weight of 3.53 × 10⁷ and 3.25 × 10⁷ g/mol were also found with sucrose and glucose. At last, the proposed mechanism of sugar metabolism and xanthan biosynthesis pathway were described. Conclusively, maltose appeared as the best carbon source for maximum xanthan production: while sucrose and glucose gave qualitatively best results. In short, this systematically modelled approach maximizes the potential output and provides a solid base for continuous cultivation of xanthan at large-scale production.
... Shen et al. compared this with the prebiotic role of OG and barley β-glucan, who found that the mice intestines with OG were higher than that of barley β-glucan in the number of Lactobacillus and Bifidobacterium, which better promoted intestinal health [9]. Gee et al. studied the effects of barley β-glucan on the growth of two yogurt starter cultures composed of Streptococcus thermophilus and Lactobacillus denderi, subspecies Bulgarian, respectively, and Molecules 2021, 26, 4752 2 of 10 who found that the barley β-glucan had no adverse effect on probiotic growth [10]. Ibrahim et al. studied the effects of OG and/or bifidobacterium producing exopolysaccharide on the physical properties, fermentation time, and sensory evaluation of low-fat yogurt, and the result showed that the OG and bifidobacterium produced exopolysaccharide in low-fat yogurt, improved the physical and sensory properties of yogurt, and enhanced probiotics activity [11]. ...
... Color Uniform color, milky white or milky yellow (7-10) 10 Different colors (4)(5)(6) Structural state Good coagulation, fine and uniform structure, no whey precipitation (25)(26)(27)(28)(29)(30) 30 Good coagulation, fine and uniform structure, a small amount of whey precipitation (15)(16)(17)(18)(19)(20)(21)(22)(23)(24) Poor coagulation, different structure, and serious whey precipitation (0-14) ...
... The taste is smooth and delicate, with thickness and viscosity (25)(26)(27)(28)(29)(30) 30 The taste is smooth and delicate, with thickness and viscosity (15)(16)(17)(18)(19)(20)(21)(22)(23)(24) The taste is not smooth, delicate, and astringent (0-14) ...
The oat β-glucan (OG) was added into set-type yogurt as a functional ingredient, in order to evaluate effects on the rheological characteristics and microstructure of set-type yogurt. When the OG concentration increased from 0 to 0.3%, the WHC gradually increased. At 0.3% OG, the set-type yogurt had the highest WHC of 94.67%. Additionally, the WHC continuously decreased, reaching the lowest WHC (about 80%) at 0.5% OG. When 0.3% OG was added, the highest score of sensory evaluation was about 85. The rheological result showed that the fermentation process went through the changes as follows: solid → liquid → solid → liquid. The addition of 0.3% OG decreased the fermentation time of set-type yogurt by about 16 min, making yogurt more inclined to be liquid. The acidity of set-type yogurt with OG was slightly higher. The result of microstructure showed that the addition of OG destroyed the three-dimensional network structure of yogurt, and some spherical aggregate particles could be clearly observed at 0.3% OG. Overall, this study provided a theoretical basis for the application of OG in set-type yogurt.
... Furthermore, it contributes to the structural stability of the yogurt. [75] The improved rheological attributes of the yogurt with added crosslinked starches could be due to the development of starch gel and further strengthening of the starch gel network by crosslinking. It will contribute to the viscoelastic characteristic of the yogurt. ...
... Furthermore, the interaction of protein and starch will also contribute to increased rheological attributes of starch-incorporated yogurt, and this network is formed by hydrogen bonding. [75] Ice cream is a dairy-based product that contains a high proportion of fat. Surendra Babuet al. [32] reported the impact of the addition of different levels of citric acid crosslinked starch (1 and 2%) to ice cream containing different levels of fats (6% and 1%). ...
The industrial food applications of native starches are limited due to their limited resistance to shear, susceptibility to thermal decomposition, and high tendency for retrogradation. Cross-linking of starches adds intra and inter-molecular bonds at various locations in the starch molecule that result in the stability of the granule and enhance functional attributes. This process involves the use of various cross-linking agents such as sodium trimetaphosphate (STMP), sodium tripolyphosphate (STPP), epichlorohydrin (EPI), phosphorus chloride (POCl3), and citric acid, etc., to introduce covalent or non-covalent linkages between starch molecules. Cross-linked starch exhibits improved resistance to retrogradation, enhanced freeze-thaw stability, and increased stability during cooking, shearing, and processing, such as high or low temperatures and pH. This review paper offers an overview of cross-linking modifications, emphasizing their importance in addressing native starch limitations. It underscores the significance of selecting appropriate cross-linking agents to customize starch properties for specific applications. Furthermore, the paper discusses the properties and applications of cross-linked starches and delves into regulatory considerations regarding their use. Regulatory consideration for cross-linked starches has also been discussed. Cross-linking modifications offer a promising avenue to unlock the full potential of starch and expand its utility across a wide range of applications.
... Foods 2020, 9, 957 2 of 15 mouthfeel and creaminess, and reduced syneresis of yoghurt [8,9]. Several researchers have reported the application of cereal or tuber starches as stabilizers in yoghurt manufacture [9][10][11][12][13]. ...
... The yoghurt was prepared in triplicate, as described by Cui et al. [8]. Two litres of commercial homogenized and pasteurized milk were fortified with 2% (w/v) skimmed milk powder (SMP); 2% (w/v) sucrose was added as sweetener, followed by addition of 1.5% (w/v) acetylated or native pigeon pea starch as the stabilizer, and then, mixed thoroughly. ...
The behaviour of graded acetylated pigeon pea starch during heat processing was evaluated in addition to the corresponding effect of their incorporation at 1.5% (w/v) as a stabilizer in set-type yoghurt. Acetylated starch possessed higher solubility and swelling power than native starch under the temperature regimes considered. Addition of acetylated pigeon pea starch as a stabilizer in yoghurt had positive influence on the water holding capacity (7.7% to 10.4% compared to 13.3% in yoghurt stabilized with native pigeon pea starch) and whey syneresis (approximately 15%, 12%, and 8% increase observed in yoghurt with acetylated pea starch compared to 47% in yoghurt with native pea starch stabilizer) at the end of a 28-day cold storage period. In addition, pea starch-stabilized yoghurt possessed an enhanced sensory attribute (firmness), and compared favourably with gelatin-stabilized yoghurt in terms of overall acceptability. Thus, acetylated pigeon pea starch exhibited improved physicochemical properties and showed usefulness as a stabilizer in yoghurt because it enhanced the physicochemical, storability, and sensorial quality, while improving the body and texture of the product.
... Furthermore, the incorporation of acetylated starch improved the flow characteristics of the yogurt. Moreover, the hydrogen bonding between proteins and starches could enhance the rheological properties of yogurt containing starch [160]. Ice cream, characterized by its significant fat content, is commonly derived from milk. ...
Starch is among the most abundant natural compounds in nature after cellulose. Studies have shown that the structure and functions of starch differ extensively across and among botanical types, isolation procedures, and climate factors, resulting in starch with significant variations in its chemical, physical, morphological, thermal, and functional characteristics. To enhance its beneficial properties and address inherent limitations, starch is modified through various techniques, resulting in significant alterations to its chemical and physical characteristics. These structural modifications impart considerable technological and industrial versatility. In the food sector, modified starch serves as a thickener, shelf-life extender, fat replacer, texture modifier, gelling agent, and stabilizer. In non-food applications, it functions as a sizing agent, binder, disintegrant, absorbent, and adhesive and is employed in construction as a sealant and to improve material bonding strength. The demand for modified starch has surpassed that of its native counterpart, reflecting its growing market value and the industry's interest in products with novel functional attributes and enhanced value. This study focuses on rice starch, highlighting its structure and composition and their impact on physicochemical properties and functionality. Additionally , it examines the enhancement of its techno-functional characteristics, achieved through various modification processes.
... In thixotropic fluids, structural rebuilding occurs after the stress is removed, indicating a weak gel structure in the yogurt. This suggests that in the treated samples, reconstructing the protein network into a cohesive structure after shearing is more challenging compared to untreated yogurts (Cui et al. 2014). ...
Yogurt is a popular milk‐based product known for its nutritional benefits and effects on the large intestine. However, yogurt production faces challenges like texture, consistency, and syneresis. Hydrocolloids, such as gums and polysaccharides, can enhance yogurt's consistency and rheological properties. This research evaluates rooster comb extract (RCE) as a natural additive to improve stirred yogurt's properties during 21 days of storage at 4°C. Two treatments with 0.8 and 0.9 g of RCE were added to stirred yogurt. Results showed a decrease in pH (from 3.89 to 4.38) and microbial counts (> 10⁷ log CFU/g), along with an increase in titratable acidity (1.03%–1.48%) in RCE‐enriched yogurt (p < 0.05). The 0.8 g RCE treatment showed reduced syneresis, lightness, and setting time compared to the control (p < 0.05). Rheological analysis indicated thixotropic shear‐thinning behavior, accurately described by the Herschel–Bulkley model. All samples displayed solid viscoelastic properties, with the storage modulus exceeding the loss modulus in the linear viscoelastic region. While flavor and overall acceptability declined in enriched samples compared to controls (p < 0.05), no significant differences were found in other characteristics, including texture, color, and aroma (p > 0.05). In conclusion, RCE is a promising natural hydrocolloid for producing functional stirred yogurt, offering potential consumer benefits.
... Except for sample B0, which showed dilatant fluid behavior, all other samples showed flow behavior values lower than 1, as the velocity gradient increases, the particles tend to present a more ordered behavior, indicating that there is a decrease in yield strength, confirming their pseudoplastic behavior. Cui et al. (2014) reported that this behavior may have occurred due to the breaking of protein bonds with the increase in the shear rate. Gorji et al. (2023), Zhang et al. (2020), and Melito and Daminiano (2015) reported similar results for this parameter, working with different concentrations of GG and xanthan gum in binary mixtures of these irradiated biopolymers, their hydrophobic derivatives, and on the stability of curd sauce. ...
This study aimed to investigate the static and dynamic rheological properties of an ultra‐processed powdered goat milk beverage containing carboxymethyl cellulose (CMC), guar gum (GG), and xanthan gum (XG), using a mixture design. Fourteen samples were evaluated, in addition to the original beverage. The flow curves classified the fluids as non‐Newtonian and characterized all the reconstituted beverages with pseudoplastic behavior, precisely due to the addition of hydrocolloids that increased the viscosity, and the fresh beverage sample showed the behavior of a dilatant fluid. The stress sweep verified the changes in the storage module (G′) and the loss module (G″), the G′ ranged from 1.97 to 20.36 (Pa) and the G″ ranged from 5.94 to 11.30 (Pa), demonstrating that there was the formation of beverages with elastic and viscous behaviors. The results showed a synergistic effect between the texture improvers, and the formulations with GG identified a greater effect on the tension. The frequency sweep tests showed that the behavior of the samples was that of a weak gel; however, when subjected to a certain frequency, the values of G′ exceeded the value of G″, becoming a sample with more elastic characteristics and consequently, presenting the behavior of a stronger gel. Finally, according to the data presented, it is assumed that formulations containing GG and xanthan gum may produce desirable consumer properties for the reconstituted goat milk drink. Samples with a higher concentration of GG exhibited improved rheological performance, characterized by greater consistency, increased resistance to tension, and higher viscosity at low frequencies.
Practical Application
The powdered goat milk drink is an innovative product that meets the demands of the food industry and consumers by offering a nutritious and sustainable beverage alternative.
... Modified starch is favored by manufacturers because of its high production efficiency [5,59] . It is divided into anionic polysaccharide and neutral polysaccharide. ...
... Additionally, acylated starch has low gelatinization temperature, high paste viscosity, high paste transparency, low gelling ability, and high freezing resistance, so it can be used as a thickener and anticoagulant in the food industry to improve food quality. For example, it is added to set yogurt as a thickening agent (Cui et al. 2014;Pang et al. 2019). In addition, acylated starch, as a type 4 resistant starch, not only has certain processing properties but also has potential prebiotic properties, which can be further fermented in the gut to produce and release more SCFAs (Hong et al. 2016). ...
Short-chain fatty acids (ScFAs) are the primary energy source of colonic epithelial cells, but oral ScFAs are digested, absorbed, or degraded before reaching the colon. the acylated starch with ScFAs can be fermented and release specific ScFAs under the action of colonic intestinal microbiota. this review first introduces the preparation method, reaction mechanism, and substitution factors. Second, the structure, physical and chemical properties, in vitro function, and mechanism of acylated starch were expounded. Finally, the application of acylated starch in foods is introduced, and its safety is evaluated, providing a basis for the further development of acylated starch-based foods. the acylated starch obtained by different acylation types and preparation methods is different in particle, molecular, and crystal structures, leading to changes in the function and physicochemical properties. Meanwhile, acylated starch has the functional potential of targeted delivery of ScFAs to the colon, which can increase ScFAs in feces and intestine, selectively regulate the intestinal microbiota, and produce a prebiotic effect conducive to host health. the safety of acetylated starch has been supported by relevant studies, which have been widely used in various food fields and have great potential in the food industry.
... Despite their low cost, availability on the market and technological advantages, starch products are still used quite limitedly in dairy industry (Polischuk et al., 2019;Zargaraan et al., 2016). At the same time, glucose-galactose syrup (Mosquera-Martínez et al., 2023) and chemically modified starches (Cui et al., 2014;Schmidt et al., 2007) are more widely used in yogurt production. Meanwhile, functional waxy corn starches (CLARIA® Elite, Plus, Essential Starch), obtained from Tate & Lyle, (USA) in quantities of 1.88 and 2.35 (by nominal phase volume) demonstrated a consistent texture accompanied by the fullest taste. ...
... Yao et al. [37] applied acetylated cassava starch nanoparticles as an emulsion stabilizer; it was reported that acetylated starch nanoparticles improved hydrophobicity and improved emulsion capacity by improving the droplet size and homogeneity so that the storage stability increased up to 35 days. Cui et al. [38] applied cross-linked acetylated cassava starch to the manufacture of set yogurt, and it was reported that cross-linked acetylated cassava starch improved the stability, viscous modulus, and elastic modulus of the set yogurt. Meanwhile, Osman et al. [16] utilized acetylated corn starch as a fat replacer in beef patties, and it was found that it was suitable as a fat replacer for meat products. ...
Various modification treatments have been carried out to improve the physicochemical and functional properties of various types of starch and flour. Modification by acetylation has been widely used to improve the quality and stability of starch. This review describes the effects of acetylation modification and its dual modifications on the physicochemical properties of starch/flour and their applications. Acetylation can increase swelling power, swelling volume, water/oil absorption capacity, and retrogradation stability. The dual modification of acetylation with cross-linking or hydrothermal treatment can improve the thermal stability of starch/flour. However, the results of the modifications may vary depending on the type of starch, reagents, and processing methods. Acetylated starch can be used as an encapsulant for nanoparticles, biofilms, adhesives, fat replacers, and other products with better paste stability and clarity. A comparison of various characteristics of acetylated starches and their dual modifications is expected to be a reference for developing and applying acetylated starches/flours in various fields and products.
... Other studies have revealed similar trends, increased acidity and decreased pH in fermented milk beverages and yoghurts with the addition of modified corn and cassava starch. 18,19,20 The data presented is the average of three replicates with standard deviation. * -indicate significant differences control group and others (P ≤ 0.05), ** -indicate significant differences native group and others (P ≤ 0.05). ...
The present studies have examined the effect of potato starches treated with amylase B.licheformis (Bl) (laboratory sample) or Amylosubtilin® (AM) (Berdsk Factory of Biological Preparations (now: Sibbiofarm), Russia) in different concentrations on the quality of Slavic skim milk drink Varenets made from baked milk. The baked milk is milk heated to 98 °C for 3 hours, it has a sweet aroma and taste and creamy hue. The presence of enzyme-modified potato starches (Bl or AM) has been found to promote the activation of lactic acid fermentation, the accumulation of exopolysaccharides, and such stabilized products have a higher viscosity, a lower percentage of syneresis compared to the control sample. The antioxidant capacity of the Varents samples after fermentation was evaluated by two assays: analysis of radical capture activity of 2,2-diphenyl-1-picrylhydrazyl (DPPH •); and the ability to restore Fe + 3 (Iron Reduction Antioxidant Ability Assay, FRAP). All Varentz samples showed different values for DPPH, FRAP assays depending on the starches used. The Introduction of pre-fermented starches into defatted jam promotes formation of enhanced antioxidant properties of milk product. The use of starches modified with enzymes improves sensory characteristics, in particular, as a fat imitator, formsfull taste of the drink.
... Among the native and oxidised starch samples prepared in the present work, oxidised starch made with 2.0% sodium hypochlorite showed a better potential for improving the WHC, apparent viscosity, and sensory score of set yogurt, and starch made using 3.0% sodium hypochlorite showed the next-best potential. This phenomenon might have been due to the fact that the presence of oxidised starch could increase the strength and molecular tightness of the gel network in set yogurt, and to a certain extent, the intensity of this effect increases as the degree of oxidation in the starch increases (Cui et al., 2014). However, the WHC of yogurt prepared with 4.0% oxidised starch was lower than those of yogurt prepared with 2.0 and 3.0% oxidised starch. ...
Potato starch was modified by oxidation with different concentrations of active chlorine (0.5, 1.0, 2.0, 3.0, and 4.0%); and the physicochemical properties of the oxidised potato starch samples and the use of these starches in set yogurt were investigated as a function of their degree of oxidation. The carboxyl content, carbonyl content, and solubility of the oxidised starches increased with increasing sodium hypochlorite concentrations, while the swelling power decreased. Scanning electron microscopy showed that oxidation caused cracks or pores on the surfaces of the starch granules, and these morphological changes were enhanced by increased oxidant concentrations. Analysis with a Rapid Visco Analyser showed that high degrees of oxidation could improve the starch thermodynamic stability and resistance to retrogradation. Set yogurts made with oxidised potato starches had higher water-holding capacities, higher apparent viscosities, and better sensory qualities than those prepared with native starch.
... The six groups of yogurt all showed shear thinning behavior, consistent with previous studies (Xu et al., 2019). According to Cui et al. (2014), this pseudoplastic phenomenon was caused by the breaking of protein bonds. Compared with the low-fat yogurt control, the samples containing TFPS showed a higher apparent viscosity. ...
The potential of Tremella fuciformis polysaccharides (TFPS) as a fat substitute in low-fat yogurt was evaluated in this study. The effects of adding different concentrations of TFPS solution on the physical and chemical properties, texture, rheology, microstructure and sensory properties of low-fat yogurt were evaluated. Compared with control, the addition of TFPS not only increased the solid content and water holding capacity of yogurt, but also reduced syneresis losses in low-fat yogurt. In fact, the addition of TFPS did not affect the color of yogurt but had a positive effect on the texture and sensory of yogurt. In terms of rheology, all low-yogurt samples exhibited rheological to the weak gel-like structures (G' > G″), and the storage modulus and loss modulus of the yogurt added with TFPS were higher than those of the low-fat yogurt control group. Compared with the low-fat yogurt control group, yogurt added TFPS makes the cross-linking of polysaccharides and casein more compact. In conclusion, TFPS has potential as a fat substitute in dairy products.
... Based on the Oswald-de Waele power law model, yoghurts fortified with CUBTAM made from both fermentation processes can be considered as non-Newtonian fluids with shear-thinning behaviour due to the flow behaviour index (n) below 1. The breakage of bonds between the protein aggregates as a consequence of shear stress led to the pseudoplastic behaviour of the yoghurt samples [49]. The consistency index (K) and flow behaviour index (n) of yoghurts were not significantly influenced by the fermentation process, whereas the increase of encapsulated powder concentration led to the increase of K and decrease of n values. ...
Tamarillo extract is a good source of phenolic and anthocyanin compounds which are well-known for beneficial antioxidant activity, but their bioactivity maybe lost during digestion. In this study, promising prospects of tamarillo polyphenols encapsulated in cubosome nanoparticles prepared via a top-down method were explored. The prepared nanocarriers were examined for their morphology, entrapment efficiency, particle size and stability during in vitro digestion as well as potential fortification of yoghurt. Tamarillo polyphenol-loaded cubosomes showed cubic shape with a mean particle size of 322.4 ± 7.27 nm and the entrapment efficiency for most polyphenols was over 50%. The encapsulated polyphenols showed high stability during the gastric phase of in vitro digestion and were almost completely, but slowly released in the intestinal phase. Addition of encapsulated tamarillo polyphenols to yoghurt (5, 10 and 15 wt% through pre- and post-fermentation) improved the physicochemical and potential nutritional properties (polyphenols concentration, TPC) as well as antioxidant activity. The encapsulation of tamarillo polyphenols protected against pH changes and enzymatic digestion and facilitated a targeted delivery and slow release of the encapsulated compounds to the intestine. Overall, the cubosomal delivery system demonstrated the potential for encapsulation of polyphenols from tamarillo for value-added food product development with yoghurt as the vehicle.
... The yoghurts tested in our experiments are set types, that form a dispersion system consisting of small particles that are responsible for the formation of yield stress. This parameter is defined as the initial force required to initiate the yoghurt to flow [37]. Both the addition of green tea and inulin into yoghurts influenced the yield stress. ...
The purpose of this study was to investigate the influence of the addition of inulin (3%, 6% and 9%) to green tea-infused set type yoghurt on its sensory quality and physical properties. Yogurts were made by combining green tea with milk and inulin and inoculated with freeze-dried starter cultures YO-122. Incubation was conducted at 43 °C for approximately 4.5 h until a pH value of 4.5–4.6 was achieved. For the prepared yoghurts, a panel of experts (n = 10) was selected, characterized 35 attributes and conducted a sensory quality assessment of these yoghurts using the Quantitative Descriptive Profile method. Additionally, instrumental analyses such as yield stress, adhesiveness, firmness, physical stability and color parameters were also carried out. The use of green tea infusion increased the perception of green tea flavor, bitterness, astringency, dark color of the yoghurt and the existing whey, which worsened the overall sensory quality of the yoghurt. The addition of inulin (9%) to the green tea yoghurt, increased the perception of sweet, peach flavor and aroma and improved the firmness of the yoghurt while reducing the perception of sour taste, which improved the sensory quality of the yoghurt. Both inulin and green tea affected the physical properties of the yoghurts, causing an increase in the yield stress (43%, and 20%, respectively) and deteriorated the stability of the yoghurts. Green tea affected the color of the yoghurts, causing the lightness to decrease. The L* parameter decreased from 89.80 for the control sample to 84.42 for the green tea infused yoghurt. The use of infused green tea in yoghurt production makes it necessary to use ingredients that will neutralize its adverse effects on sensory quality and physical parameters of yoghurt, and such an additive can be prebiotic fiber–inulin at a concentration of 9%.
... Similar results were observed in yoghurt fortified with apple pomace [13] and orange pomace [29]. According to Cui et al. [30], the pseudoplastic behaviour of yoghurt was due to the breakage of bonds between the protein aggregates as a consequence of shear stress. The increase in tamarillo powder concentration led to the increase in the consistency coefficient index and the decrease in the flow behaviour index. ...
Bright-red Laird’s Large tamarillo is a unique and under-utilised fruit that is a dietary source of carotenoids, vitamins C and E, and dietary fibre. The effects of the addition of freeze-dried tamarillo powder (5–15%) to milk and yoghurt starter either before (PRE) or after (POS) fermentation on physicochemical properties were examined. Using LC-MS and GG-MS, nutrient and volatile contents of tamarillo yoghurt were also examined. The addition of tamarillo prior to fermentation was associated with a more yellow colour and higher concentrations of tocopherol compared to when tamarillo was added after fermentation. Higher elastic modulus, PUFAs, pro-vitamin A content, and vitamin C retention were observed for POS than PRE. All tamarillo yoghurts showed improvement in syneresis, lower lactose content, and higher concentrations of antioxidant vitamins than the commercial premium-assorted fruits yoghurt from New Zealand Food Composition Data. Yoghurt fortified with tamarillo powder offers the potential for the development of a high-value nutritional product that could be a good source of vitamin C and a source of vitamin E and β-carotene, and maintain the volatiles that give tamarillo its distinctive flavour.
... Researchers reported the use of carboxymethyl cellulose (CMC), low-methoxyl pectin, guar, xanthan, and gellan gum, [16,19], sodium alginate, [14], and guar gum [15,17,20] in carrot, orange, mulberry, and apple juices. Starch is widely used in yogurt preparation as a thickener to reduce defects, making the body and texture of manufactured yogurt appealing as well as reducing cracks in the surface of the curd milk [18,21]. However, studies on starch addition in fruit juice for colloidal stability are relatively limited. ...
Starch is one of the most important value-added food ingredients used as a thickener in many foods and industrial applications. This research investigated the effect of different concentrations of starch (anchote and potato) addition on the colloidal stability of pineapple juice. The experiment was carried out on a two-factor factorial design arranged in CRD. The first factor (starch type with two levels (anchote and potato)) and the second factor (starch concentration with three levels (1%, 3%, and 5%)) were considered. The starch-added juice samples were preserved for 15 days at room temperature. The physicochemical properties, colloidal stability, microbial counts, and sensory analysis were conducted in a 7-day interval including the first day. The results revealed that different starch concentrations showed a significant effect (P ≤ 0:05) on the cloud stability, most of the physicochemical properties and microbial count of pineapple juice as compared to the control. The turbidity and viscosity of the juice samples were increased significantly (P ≤ 0:05) by the starch addition; in contrast, pulp sedimentation and microbial counts were decreased. As storage duration increased, turbidity, viscosity, TSS, pH, and vitamin C content of juice decreased, whereas sedimentation, TA, and microbial count increased. The results revealed that the total bacterial and fungal counts of pineapple juice samples were rising as storage durations increased. The maximum cloud retention was observed in juice added with 5% anchote starch. Finally, it is confirmed that starch (anchote and potato) addition positively affected the colloidal stability of pineapple juice and also possessed high potential to extend the shelf life.
... To date, the effect of some substances on yoghurt microstructure had been disclosed; for example, pomace containing insoluble fibres as well as soluble components could reduce whey separation and bring about compact casein aggregates [8], while okra polysaccharides, apple pectin, and guar gum in yoghurt were capable of improving yoghurt microstructure and stabilizing yoghurt texture [38,39]. Furthermore, the research from Cui and coauthors also showed that application of cross-linked acetylated starch in the preparation of set-style yoghurt could cause compact microstructure [40]. The present study thus shared conclusion consistency with these mentioned four researches. ...
Yam (Dioscorea opposita Thunb.) juice was used to replace water by 10% and 20% (w/w), respectively, while the diluted yam juice was used to disperse skimmed milk powder. Set-style skimmed yoghurt samples were thereby prepared using a commercial direct vat set starter at 42 °C. Assaying results indicated that yam juice had a slight impact on the contents of total proteins and total solids of yoghurt samples but could promote yoghurt fermentation and induce texture changes. Firstly, yam juice shortened fermentation time by about 1 h and caused a higher post-acidification during yoghurt storage at 4 °C. Secondly, yam juice reduced syneresis extent during the preformed yoghurt storage, led to value increases for these textural and rheological indices like hardness, adhesiveness, cohesiveness, viscosity as well as elastic/viscous moduli, and caused a finer and compact microstructure. Furthermore, yam juice also resulted in higher viable numbers for two starter microorganisms Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in the stored yoghurt samples. However, replacing water with yam juice by 20% other than 10% occasionally showed a negative impact on some textural attributes of yoghurt samples. It is thus concluded that yam juice at suitable level could be used in the production of set-style yoghurt without significant negative effect on yoghurt compositions or its fermentation, when aiming to obtain a firm yoghurt texture and endow yoghurt with enhanced health benefits from the starter strains.
... The model that best represented the rheological behavior of yogurts with added stabilizers was the power-law model (R 2 between 93% and 99.1% and MSE between 0.030 and 1.118). This model is the most used in the rheological characterization of yogurts (Janhøj et al., 2008;Andrade et al., 2010;Oroian et al., 2011;Parra et al., 2012;Cui et al., 2014). Figure 6 shows the flow behavior index (n) of stirred-type yogurts during storage. ...
This study investigated the effect of the addition of starch from “hawthorn” yam (Dioscorea rotundata) and “creole” yam (Dioscorea alata) at different concentrations (0.1%, 0.3%, and 0.5% w/w) on the physicochemical and sensory properties of stirred-type yogurt. Pectin (0.3% w/w) was used as a reference stabilizer. Yogurt with yam starch presented 13.38% less syneresis than yogurts with pectin. At the sensory level, the most accepted treatment was yogurt with “creole” yam starch at 0.1% w/w. During 21 days of storage, yogurt with yam starch (“creole” and “hawthorn”) at 0.1% w/w showed a decrease in syneresis between 7% and 8%, while in those with pectin, syneresis remained practically constant in this period. Yogurt with yam starch was characterized as a pseudoplastic fluid, with a lactic acid bacterial count according to NTC 805. Yam starch can be used as stabilizer because it improves the physicochemical, sensory, and rheological characteristics of stirred-type yogurt. Especially the “creole” yam starch (0.1% w/w), which presents the best preference by consumers.
... Addition of MFE appeared to affect the gelation and cooling kinetics of the yogurt. When neutral or charged macromolecules were added to the yogurt, certain structural modifications could also be affected (Cui et al., 2014;Pachekrepapol et al., 2015;Fu et al., 2018). Monk fruit extract may interact with amino groups of amino acid residues on the casein micelles. ...
A yogurt using monk fruit extract (MFE) as a sweetener was developed. The aim of the study was to investigate the viability of using MFE to develop sweetened yogurts without the calories of added sugar. The physiochemical, rheological, microstructural, and antioxidant properties of yogurt were studied. Rheological results showed that MFE affected the yogurt fermentation process and its rheological properties. Yogurt sweetened with MFE had similar microstructural properties to yogurt sweetened with sucrose. Yogurt with MFE showed higher levels of gly-pro-p-nitroanilide and dipeptidyl peptidase IV inhibitory activities, 1,1-diphenyl-2-picrylhydrazyl radical scavenging capacity, α-glucosidase inhibitory activities, and superoxide anion radical scavenging ability (P < 0.05) compared with other yogurt samples. Results indicated that MFE could be a novel sweetener and a food antioxidant for functional yogurt and related products.
... The zeta potential values of control approached with the findings of Tan, Wang, and Moraru (2014) in skim milk at neutral pH (6.5). Increased addition of cross-linked starch (0.5-2.5%) have also been reported to result in protein aggregation and thus, lowered zeta potential in set yoghurt (Cui, Lu, Tan, Wang, & Li, 2014). The rheological behaviour of yoghurts corroborated well with the observed particle size/zeta potential, firmness and thus, reduced syneresis. ...
Addition of low-methoxyl pectin (LMP) was observed to reduce whey loss, improve firmness, rheology, quality and overall liking of low-fat set-yoghurt. LMP addition increased soluble solids content and resulted in higher bacterial counts (≥10 log CFU/g), acidity, bioactivity (DPPH• & ABTS⁺ μM Trolox/g), and lower pH of set yoghurts. A significant (p < 0.05) improvement in firmness and 16% reduction in whey loss was also observed. As per rheology studies, LMP added set yoghurts possessed higher modulus (G′, G″, G*) and complex viscosity. Power law model parameters (A & z) for G* also related to the enhanced strength of yoghurt matrix on addition of LMP. The dense packing of protein gel structure along with filling action of hydrated hydrocolloid might led to moduli changes in yoghurts. Increasing slope of |G*| and dtan δ values close to zero confirmed higher gel strength of yoghurt added with higher concentrations of LMP. Microstructure revealed open porous network of casein in control, while increased cross-linking with casein or filling of cavities was observed upon addition of LMP in yoghurts. Sensory liking scores showed strong correlation with rheological parameters, while PCA confirmed the effect of LMP concentration on major quality attributes.
... Furthermore, they can be used as fat replacers to reduce the amount of milk solids, and to reduce production costs (Alting et al., 2009;Sandoval-Castilla, Lobato-Calleros, Aguirre--Mandujano, & Vernon-Carter, 2004). Most studies in the literature on the rheological and structural properties of starch-yoghurt systems have been performed with mostly native or chemically modified starches (Cui, Lu, Tan, Wang, & Li, 2014;Nguyen, Kravchuk, Bhandari, & Prakash, 2017;Oh, Anema, Wong, Pinder, & Hemar, 2007;Zuo, Hemar, Hewitt, & Saunders, 2008). Recently, as a green and sustainable process, enzymatic modification of starch with amyloglucosidase has attracted much attention especially in producing porous granules. ...
... Concomitantly, it translates into a considerable improvement in milk utilization and the intake of valuable nutrients [25]. The formation of gel matrix via the aggregation of casein micelles arises when the pH approaches 4.5-4.6 as a result of lactic acid production during fermentation [26]. In this study, the fermentation times varied with the bacterial combination ratio; the shortest fermentation time was registered for T4 and T9 formulations, while the highest fermentation was registered for T8 ( Table 2). ...
A native Lactococcus lactis subsp. lactis UTNGt28 (GenBank accession no: MG675576.1) isolated from Amazonian fruit of the tropical Caimitillo (Chrysophyllum oliviforme) tree and the commercial strain Lactococcus lactis subsp lactis ATCC11454 (LacAT) were targeted ex vitro in whole milk in combination with Streptococcus thermophilus ATCC19258 to obtain a fermented probiotic beverage. Concomitant with cell viability determination during storage (28 days), the pH, titratable acidity, syneresis, protein and fat were evaluated. The results indicated that neither UTNGt28 nor LacAT displayed a high capacity to ferment whole milk and survive during storage; a statistically significant difference (p < 0.05) in cell viability was registered for UTNGt28 compared with LacAT when inoculated alone or in combination with S. thermophilus. A principal component analysis showed a clear difference between the yogurt formulations at day 1 and 28 of storage. The PC 1 explained 46.8% of the total variance (day 28), was loaded in the negative (−) direction with titratable acidity (% lactic acid), while the PC 2 explained 22.5% (day 1) with pH. PC 1 was loaded in the positive (+) direction with pH, cell viability, syneresis, fat and protein. Overall results indicated that UTNGt28 has the technological properties for further development of a new probiotic product.
The rheology of yogurt, a critical factor influencing its texture, stability, and sensory appeal from production to consumption is explored in this review. Yogurt undergoes a transformation from a Newtonian liquid to a non‐Newtonian thixotropic gel during fermentation, a process shaped by factors such as milk source, starter culture, and fat content. Recent advances in non‐thermal treatments, such as ultrasound, microfiltration, high‐pressure processing (HPP), and ultraviolet C (UV‐C) light treatment, promise to enhance nutritional and sensory qualities of yogurt. Additionally, incorporating herbs and fruits into yogurt not only diversifies consumer options but also affects its texture, viscosity, and overall mouthfeel. The review examines how different yogurt styles—set, stirred, Greek, and drinkable—develop unique textures through varied production processes. Advances in rheological techniques and microstructural analysis have deepened our understanding of the interactions between proteins and fat globules, providing insights into the complex gel network of yogurt. Despite significant progress, further research is needed in areas such as non‐destructive rheological testing during production, the impact of extended storage, and the development of plant‐based yogurt alternatives. The insights are valuable for the dairy industry to support innovation and meet growing consumer demands.
In this study, the effect of different acetylated distarch phosphate (ADSP) ratios (0, 1%, 2%, 3%, 4%, 5%) on the physicochemical characteristics and stability of the oyster sauce (OS) system was investigated. The texture, water state, interactions, rheological properties, microstructure, and stability of OS samples were analyzed through the texture analyser, low-field nuclear magnetic resonance (LF-NMR), particle diameter and zeta potential, fourier-transform infrared spectroscopy (FTIR), rheometer, and microscopes. The results revealed that the addition of ADSP improved the firmness, consistency, cohesiveness, and water-holding capacity of OS. Moreover, ADSP reduced the average particle size and zeta potential of OS, indicating that electrostatic and steric stabilization existed in the ADSP-OS system. The addition of ADSP enhanced the hydrogen bonding and decreased water mobility for OS system, processing a more continuous and smooth structure. All ADSP-OS samples were typical non-Newtonian fluids with shear-thinning characteristics. In addition, the non-significant instability index changes of ADSP-OS over the whole storage period confirmed the excellent long-term stabilization capability of OS prepared with ADSP. This study provides a theoretical basis for starch-based sauce products and contributes to the development of sauce products.
The sol performance of wheat starch (WS) matrix incorporating acetylated starch (AS) is crucial for the processing and quality features of wheat products. From a supramolecular structure view, how regulating salt (sodium chloride) concentration modulates the sol features, e.g., pasting, zero-shear viscosity (ZSV) and thixotropy of WS-AS binary matrix was explored. Compared to the salt-free counterpart, the saline matrices exhibited a delayed pasting profile and a decreased viscoelasticity. Thereinto, the sol at 0.02 M NaCl exhibited the smallest ZSV (23,710 Pa·s) and the greatest in-shear recovery ratio (33.7 %). Such variations could be attributed to the weakened coil-helix, nematic-smectic and isotropy-anisotropy transitions from a side-chain liquid-crystalline perspective. Meanwhile, the correlation length (ξ) and radius of gyration (Rg) obtained from small angle X-ray scattering analysis were increased by 5.2 and 9.6 Å respectively, which disclosed a restrained entanglement and an enhanced chain mobility. These results would provide a reference for the design of fluid/semisolid products with optimized qualities.
This paper aims to overview the influence of different gels that including hydrocolloids and oleogel on techno-functional changes of dairy foods. The hydrocolloids are widely added to dairy products as stabilizers, emulsifiers, and gelling agents to enhance their texture, or improve sensory properties to meet consumer needs; and the newly developed oleogel, which despite less discussed in dairy foods, this article lists its application in different dairy products. The properties of different hydrocolloids were explained in detail, meanwhile, some common hydrocolloids such as pectin, sodium alginate, carrageenan along with the interaction between gel and proteins on techno-functional properties of dairy products were mainly discussed. What’s more, the composition of oleogel and its influence on dairy foods were briefly summarized. The key issues have been revealed that the use of both hydrocolloids and oleogel has great potential to be the future trend to improve the quality of dairy foods effectively.
Reduced-fat food has become a popular choice among contemporary consumers. This study aims to develop a starch-based fat substitute and incorporate it into reduced-fat milk gel acidified with glucono-δ-lactone (GDL) to achieve similar rheological properties as a full-fat gel. The gel properties of the fat substitute were assessed. The study examined the rheological properties, syneresis, textural properties and microstructure of acidified milk gels while also monitoring acidification process. Starch hydrolysates with low dextrose equivalent (DE) (<5.1 %) can serve as an effective fat substitute due to their excellent gelling properties The rheological and textural properties of the reduced-fat acidified milk gel with DE at 3.1 % of starch hydrolysate and 30 % fat substitution are similar to those of the full-fat milk gel. The syneresis and confocal laser scanning microscopy (CLSM) results indicated that the microstructure of the reduced-fat acidified milk gel was similar to the full-fat version. Moreover, the sensory properties of the reduced-fat acidified milk gel were acceptable when the DE was 3.1 %, and 30 % fat was replaced. In our study, we utilized hydrolyzed starch to produce reduced-fat acidified milk gels, which could potentially be used in the development of reduced-fat yogurt formulations.
Yogurt sevib istemol qilinadigan mahsulotlar ro’yhatida eng yuqoridan joy oladi. Afsuski yogurt tarkibidagi sut shakari nomi bilan mashxur bo’lgan laktoza mavjud bo’lib ba’zi bir iste’molchilar organizmi bu modda istemolida qiyinchiliklarga uchraydi va bir qator noqulayliklar keltirib chiqairadi. Shu narsani oldini olish maqsadida jahon tajribasida yogur ishlab chiqairsh jarayonida laktozani to’liq parchalash amaliyoti qo’llaniladi. Lekin bu jarayon yogurtning sifatiga qanday ta’sir ko’rsatishi quyidagi tadqiqotning asosiy maqsadi hisoblanadi va turli xil boshlang'ich laktazasiz(ferment) va laktaza birikmalaridan foydalangan holda laktozasiz yogurtning reologik xususiyatlarini baholash. Reologik tahlil davomida ferment kontsentratsiyasiga va starter va ferment birikmalariga qarab laktoza gidrolizlanishining yogurt xususiyatlariga ta'siri o'rganildi Barcha yogurt namunalari uchun yopishqoqlik natijalari bo'yicha sezilarli farqlar (p<0,05) aniqlandi.
Side effects of fat intake and consumers’ awareness have forced the food industry to produce healthier food. In recent years, non-fat yogurt has increasingly been consumed all over the world. In this study, the effect of adding a mixture of inulin, whey protein isolate, modified starch with different levels (0.3, 0.5 and, 1%) and gelatin (0.2%) on biochemical (pH, titratable acidity (TA), and Redox potential), rheological, and sensory properties of non-fat set yogurt was investigated. The samples containing higher levels of whey protein were better treatments regarding biochemical, sensory and rheological properties. The highest syneresis was observed in control yogurts and the samples with 1% inulin, whereas no syneresis was observed in samples containing 1% starch or 1% whey protein. Overall, the yogurts containing 1% whey proteins, 0.5% modified starch, 0.3% inulin, and 0.2% gelatin showed the most desirable characteristics of non-fat yogurt.
Resistant starch (RS) in recent times has gained a lot of interest in scientific research due to its numerous health benefits. It is also known as a prebiotic and a functional ingredient. There are five types of RS in which RS1 and RS2 are naturally available, and the remaining three are obtained from the modification of starch by physical (RS3), chemical, enzymatic (RS4), and addition of lipid (RS5). Incorporating the five types of RS as a functional ingredient in various food products has been done worldwide. In particular, the incorporation of RS in dairy products provides low‐cost health products that are feasible for people all around the world. RS as a prebiotic combined with probiotics present in the dairy product produces synbiotics which is more beneficial than consuming RS via other food products. Combining prebiotics and probiotics has a healthier impact on the human body. The accumulation of data regarding the different types of RS incorporated in dairy products is given in this review. To better serve today's consumers, researchers should look for low‐cost, high‐nutritional‐value products. It can be fulfilled by the resistant starch incorporated in dairy products. Although starch and milk were widely available, they were largely underutilised. We can make a variety of healthy food products by modifying and combining these ingredients. The RS in dairy products acts as a stabiliser, a source of food for microorganisms, and a fat substitute. This review's goal is to provide knowledge on these topics.
In the present study, clove essential oil (CEO) Pickering emulsions were stabilized by octadecylamine -modified carboxymethyl curdlan (CMCD-ODA) at different pH values. The droplet size and negatively charged zeta potential of the CMCD-ODA emulsions decreased as the pH increased from 3.0 to 11.0. Rheology results indicated that the CMCD-ODA polymer/emulsion prepared at pH 5.0 showed higher apparent viscosity and viscoelasticity than other pH conditions, which might prevent droplets from flocculating. The Pickering emulsions obtained at pH 5.0 were spherical droplets with a uniform size distribution and a mean diameter of 9.54 μm, and they exhibited excellent stability during 28 days of storage. The morphological structures of the emulsions investigated by confocal laser scanning microscopy and scanning electron microscopy indicated that the CMCD-ODA Pickering emulsion obtained at pH 5.0 was stabilized by loading amphiphilic CMCD-ODA polymer around the spherical oil droplets and forming a weak gel network structure. The CEO-loaded CMCD-ODA emulsions had higher antioxidant capacity than free CEO after 28 days of storage at pH 5.0. Given the good emulsion stability, antioxidant activity, and great inhibitory effect, the CEO-loaded carboxymethyl curdlan Pickering emulsion has promising applications in food, cosmetic, and biomedicine industries.
Growing interest among consumers regarding sustainable food production has led to innovations in the use of cleaner additives and manufacturing methods for the food industry, such as the enzymatic modification of starches. The effect of enzymatic modification (pullulanase and amyloglucosidase) on the pasting and thermal properties of cassava starch and the quality properties of fermented dairy beverages was analyzed at the beginning and end of a 20‐day storage period and compared to beverages with chemically modified starch (ADA), native cassava starch (NAT), without the addition of starch (control), and a commercial beverage. Amyloglucosidase‐modified starch showed the highest degree of long‐term retrogradation, which could also be perceived in the quality of beverages during storage. Beverages prepared with pullulanase‐modified starch had the highest viscosity (503.56 mPa.s) among the evaluated beverages and a lower syneresis (29.18 g/100 g) than control and NAT beverages. The addition of enzymatically modified cassava starch led to a significant increase in the general and textural acceptability of the beverages compared to the control treatment. The results show that pullulanase‐modified starches have the potential to replace chemically modified starches in the production of fermented dairy beverages, enabling the development of products that meet the requirements of the natural foods market. This article is protected by copyright. All rights reserved
The study intended to explore the influence of corn resistant starches type III (RS3s) prepared by autoclave, debranching, and microwave heat on the rheology, structure, and viable counts of set yogurt. The rheological analysis suggested that RS3s enhanced the elastic and viscous modulus of yogurt, and that microwave-heated RS was the most effective for improving viscoelasticity. Fitting the creep data using the Burger model showed that yogurt with microwave-heated RS increased the structural strength of yogurt, which displayed the highest instantaneous and viscoelastic deformations. The confocal laser scanning microscopy and scanning electron microscopy micrographs demonstrated that autoclaved and debranched RS3s formed large fragments and disrupted the continuity of the milk protein structure; however, microwave-heated RS evenly filled the gel network and formed an interpenetrating network with proteins. The bacterial count and acidity of yogurt indicated that microwave-heated and debranched RS3s promoted the growth of lactic acid bacteria and accelerated the fermentation process of yogurt. The results of this study demonstrated that microwave-heated RS is a favorable supplement to the microstructure and rheological properties of yogurt compared with autoclaved and debranched RS3s.
This study aimed to investigate the structural characteristics and physicochemical properties of mung bean protein (MBP) at different pH levels. Structures and physicochemical properties were evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, circular dichroism, ultraviolet visible and fluorescence spectrophotometry, differential scanning calorimetry, etc. MBP contained six bands of 64, 62, 48, 32, 25 and 23 kDa, among which the 64, 48 and 32 kDa bands consisted of glycoproteins. The β-sheets and random coils of MBP had structures close to double α-helices and β-turns at pH 3.0, 7.0 and 9.0. MBP in an alkaline environment had higher solubility and free sulfhydryl contents, smaller particle sizes, and lower surface hydrophobicity. Rheological analysis showed that MBP at pH 3.0, 5.0, 7.0 and 9.0 exhibited shear-thinning pseudoplastic fluids. A higher shear stress was needed to initiate flow at pH 5.0 than at pH 3.0, 7.0 or 9.0. MBP (130 mg/mL) formed self-supporting gels at pH 7.0 and 9.0. MBP had good foaming capacity (125.00 %), emulsion activity index (117.05 m²/g) and emulsion stability index (20.86 min) in alkaline environment. These results provide fundamental information about MBP for use in neutral and alkaline environments as a functional food ingredient.
In the current study, thermal-denatured whey protein-milk fat emulsion gel microparticles (WPI-EGs) were used as stabilizers and fat replacers in low-fat yogurt. The effects of emulsion gel microparticles were studied on the texture, rheology, microstructure, and sensory evaluation of low-fat yogurt. The results showed that yogurt with WPI-EGs had a better (p < 0.05) water-holding capacity. The hardness of low-fat yogurt (1.50% (wt/wt) fat) added with WPI-EGs (1.5% LF-EY) increased (p < 0.05) significantly compared than skim yogurt and whole fat yogurt. Results from scanning electron microscopy showed that with the addition of WPI-EGs, yogurt has a more compact network structure and smaller pores. This study shows that WPI-EGs can be used as an effective fat replacer and stabilizer in yogurt. WPI-EGs have broad application prospects in dairy products, such as low-fat ice cream and processed cheese.
Acidified milk is normally divided into drinking (e.g. acidified milk drinks) and gelling (e.g. stirred/set yoghurt) types, and its texture is mainly determined by the state of casein micelles. Polysaccharides are widely applied as stabilizers in controlling the texture of acidified milk. On one hand, ionic polysaccharides can provide casein micelles with electrostatic repulsion and steric hindrance to ensure their dispersion so as to maintaining uniformity and fluidity of acidified milk drinks. On the other hand, both ionic and non-ionic polysaccharides can participate in the formation of acid-induced milk gel, which would result in improved texture and reduced wheying-off in acidified milk gel. In this study, firstly, the mechanisms of suspending casein micelles by commonly used ionic polysaccharides are reviewed. Secondly, the effects of both ionic and non-ionic polysaccharides in the formation of acidified milk gel are discussed. It is revealed that depending on the different interaction mechanisms of polysaccharides with casein, suitable polysaccharide stabilizers can be selected to meet the typical texture of acidified milks (drinking and gel types).
In the present study pomace obtained from orange juice extraction was dried at70°C. The pomace powder was utilized for enrichment of yoghurt at three different concentrations viz. 1, 2 and 3%. The physicochemical and sensory properties of the yoghurt samples were evaluated during refrigerated storage and compared with control sample. The acidity increased with increase in concentration of the pomace powder and also with duration of storage. Syneresis of the enriched samples were found to be lower than that of control, but increased with level of enrichment. During storage syneresis decreased and then increased with duration of storage. Firmness was found to decrease with level of enrichment as well as duration of storage. The consistency index increased with level of enrichment, but during storage it initially increased and then decreased. Sensory studies showed that yoghurt enriched with 1% pomace powder was acceptable to the panellists.
The use of chemically modified starches to improve the physical properties of non-fat stirred yoghurt was investigated. Yoghurts were prepared from non-fat milk powder, sucrose, water and tapioca starch acetates (TSA-1, TSA-2, TSA-3), tapioca distarch phosphates (TDP-1, TDP-2, TDP-3) or native tapioca starch at 1% (w/w). Syneresis, particle size distribution and viscoelastic properties of the yoghurts were determined, and flow behaviour was described using the Herschel-Bulkley model. Furthermore, interactions between milk proteins and modified starches attributed to protein surface hydrophobicity were characterized. Results showed that yoghurts with starch acetates exhibited higher yield stress, consistency coefficient (K) values, hysteresis loop area, storage modulus (G′) and loss modulus (G″). Protein surface hydrophobicity was significantly influenced by the addition of starch acetates, and TSA-3 yoghurt exhibited the lowest values. This study concluded that the addition of TSA-3 starch showed better results in terms of the rheological properties of non-fat yoghurt.
The effect of high methoxy pectin on the behaviour of model acid milk drinks has been investigated using viscometry, laser diffraction size measurement and microelectrophoresis. The results of these different tests are interpreted using the theory of colloidal stability. With increasing pectin concentration, the behaviour changes from flocculated with few particles below 0.2µm diameter and shear thinning, time-dependent rheology to non-flocculated, many sub 0.2µm particles and low viscosity with Newtonian rheology. With even higher pectin concentrations, the acid milk drink remains non- flocculated, but with increasing viscosity and close to Newtonian rheology.
It is shown that pectin adsorbs to the surface of the casein aggregates and acts as a dispersing agent. Its stabilising effect cannot be explained by electrostatic repulsion, but presumably by steric stabilisation. The pectin is probably anchored to the casein surface by electrostatic attraction
Starches from broken rice grains derived from three varieties (PUSA-44, PR-106, and PR-114) were modified by hydroxypropylation with propylene oxide and esterification with adipic acid anhydride and/or vinyl acetate. Degree of substitution and acetyl contents (in parentheses) was relatively low; ranges between 0.02 (0.53%) and 0.12 (3.09%) for hydroxy-propylated cross-linked and acetylated starch samples. The acetylation and dual modification of starches increased the paste clarity, solubility, swelling power, sediment volume, and gel strength but decreased the gel elasticity in all the three varieties. However, the adhesiveness increased only upon dual modification in PUSA-44 and decreased in other two varieties. Cross-linking reduced the solubility, swelling power, sediment volume, and gel elasticity while increased the paste clarity, gel strength and adhesiveness. The physico-chemical characteristics of relatively high amylose variety PUSA-44 among three varieties were significantly lower than those from varieties with low amylose content whereas PUSA-44 had shown improved gel properties as compared to other two varieties.
The physicochemical (pH, fat and total solids content), sensory (appearance, consistency and taste), and rheological characteristics of five different commercial brands of lactic beverages were determined. Rheological measurements were obtained at 5°C and 25°C using a Brookfield rheometer. The experimental data were described by the power law and Herschel–Bulkley models. The ANOVA of the results were conducted using an incomplete block design, and using Tukey test. Samples showed a significant difference (P⩽0.05%) for fat content and pH. There was a significant difference in total solids content only among Nestlé (A), Batavo (C), and Parmalat (D) samples. Sensory evaluation showed more global acceptability for Nestlé; however, Nestlé and Vigor (E) lactic beverages obtained better results for appearance than for consistency and taste. Batavo obtained the best score for taste. All test samples exhibited non-Newtonian behavior, with thixotropy. Upward curves showed pseudoplastic behavior, while downward curves showed dilatant behavior with the exception of the Nestlé sample, at 25°C. Lactic beverages from all brands analyzed showed similar rheological behavior.
Milk is a complex biological fluid with high amount of proteins, lipid and minerals. The function of milk is to supply nutrients such as essential amino acids required for the growth of the newborn. In addition, due to the importance of casein and casein micelles for the functional behavior of dairy products, the nature and structure of casein micelles have been studied extensively. However, the exact structure of casein micelles is still under debate. Various models for casein micelle structure have been proposed. Most of the proposedmodels fall into three general categories, which are: coat-core, subunit (sub-micelles), and internal structure models. The coat-core models, proposed by Waugh and Nobel in 1965, Payens in 1966, Parry and Carroll in 1969, and Paquin and co-workers in 1987, describe the micelle as an aggregate of caseins with outer layer differing in composition form the interior, and the structure of the inner part is not accurately identified. The sub-micelle models, proposed by Morr in 1967, Slattery and Evard in 1973, Schmidt in 1980, Walstra in1984, and Ono and Obata in 1989, is considered to be composed of roughly spherical uniform subunits. The last models, the internal structure models, which were proposed by Rose in 1969, Garnier and Ribadeau- Dumas in 1970, Holt in 1992, and Horne in 1998, specify the mode of aggregation of the different caseins.
Food macromolecules play a crucial role in the formulation of a wide range of food products such as beverages, bread, cheese, dressings, desserts, ice-cream, and spreads. This book presents the very latest research in the area and is unique in covering both proteins and polysaccharides in the same volume. Specifically it describes recent experimental and theoretical macromolecules in solutions, suspensions, gels, glasses, emulsions and foams. Food Macromolecules and Colloids takes a fundamental approach to complex systems, providing an understanding of the physico-chemical role of macromolecular interactions in controlling the behaviour of real and model food colloids. It gives special attention to adsorbed protein layers, the stability of emulsions and foams, and the viscoelasticity and phase behaviour of mixed polysaccharide systems, as well as to the rheology and microstructure of biopolymer gels, and the interaction of proteins with lipids and aroma compounds. This attractive, typeset publication gives exceptionally broad international coverage of the subject and will make interesting reading for postgraduates, lecturers and researchers with interests in food science, surface and colloid science and polymer science.
This book is the most comprehensive introductory text on the chemistry and biochemistry of milk. It provides a comprehensive description of the principal constituents of milk (water, lipids, proteins, lactose, salts, vitamins, indigenous enzymes) and of the chemical aspects of cheese and fermented milks and of various dairy processing operations. It also covers heat-induced changes in milk, the use of exogenous enzymes in dairy processing, principal physical properties of milk, bioactive compounds in milk and comparison of milk of different species. This book is designed to meet the needs of senior students and dairy scientists in general.
Temporal dominance of sensations (TDS) methodology was used to study the influence of yoghurt composition on sensory texture and to compare results with those from quantitative descriptive analysis (QDA). Eight yoghurts with different texture characteristics were formulated varying fat, modified starch and gelatine concentration. A trained assessor panel evaluated yoghurt texture using QDA and TDS. TDS provided information about the sequence of attributes that were dominant during consumption. This methodology was useful to characterise yoghurt texture, providing information about the influence of the evaluated formulation variables that was not gathered by QDA; starch did not significantly increase creaminess intensity but it led to an increase in its total dominance. Differences between attribute intensity and dominance were higher for complex texture attributes which were evaluated throughout consumption, such as creaminess and mouth coating.
Starches of four types, from maize (normal, or chemically modified, waxy), wheat (unmodified) and rice (waxy, unmodified), have been investigated under different pasting conditions. The effect of the upper pasting temperature which is known to be of particular importance in the functional properties of starch in industrial processes has been specifically investigated. The rheological properties have been assessed from viscosity measurements (flow behaviour) at 60 °C. Gel properties upon cooling the paste were estimated through viscoelastic measurements in oscillatory shear. The main objective was to evaluate the effect of thermal treatment on the textural characteristics of a bechamel sauce, taken as a model of starch-based sauces, and prepared with the same starches in similar pasting conditions. Overall, the differences noticed in the flow and viscoelastic properties of the different starches were also found in the bechamel sauces formulated with the same starches.
Doogh is a traditional Iranian drink prepared by fragmentation and dilution of yogurt, with addition of salt and flavouring. In the present work, we have used viscometry, microscopy, particle-size analysis and measurements of serum separation to explore the effect of very low concentrations of gellan gum (0.01, 0.03 and 0.05wt %), alone or in combination with 0.25wt % high-methoxy pectin (HMP), on its structure and stability. HMP is known to prevent association of casein particles in acidic milk drinks by steric stabilisation, forming a protective layer bound electrostatically to the surface of the particles. Doogh incorporating 0.25wt % HMP alone showed satisfactory stability on storage for ∼10 days at 5°C, but after 15 days there was obvious separation into a dense sediment and a much clearer upper layer that occupied more than 80% of the total volume, which we attribute to progressive sedimentation of individual sterically-stabilised particles. Samples incorporating gellan (with or without HMP), by contrast, showed rapid development of a clear serum phase, with little further separation at longer times (up to ∼1 month), suggesting expression of fluid by contraction of a gel network (i.e. syneresis rather than sedimentation). Particle size increased dramatically (more than 10-fold) with increasing concentration of gellan, and at the highest concentration studied (0.05wt %) a continuous network of casein-rich strands was observed by phase-contrast microscopy. The concentration of NaCl used in the doogh samples (0.5wt %≈85mM) is known to be sufficient to maintain gellan in its ordered (double-helix) conformation, which has higher charge density than individual molecules of HMP. We suggest that network structure is formed by electrostatic attachment of gellan to fragments of acid-casein gel, thus increasing particle size and inhibiting surface-coverage by HMP, with weaker associations between gellan helices allowing the samples to flow. Observed decrease in serum volume with increasing concentration of gellan is attributed to formation of progressively stronger coupled networks with greater resistance to syneresis. Stabilisation of doogh with 0.05wt % gellan in combination with 0.25wt % HMP had no adverse effect on organoleptic acceptability, and reduced serum volume on protracted storage to ∼10% (in comparison with over 80% for the same concentration of HMP alone), suggesting that gellan could be of practical value in extending the shelf-life of doogh (and related acidic milk drinks).
The emulsification properties of 14 hydrocolloid gums (propylene glycol alginate, gellan, carrageenan, pectin, methylcellulose, microcrystalline cellulose, gum arabic, locust bean gum, guar, xanthan, mustard, flaxseed, fenugreek, oat) were investigated. Gum dispersions were prepared in water (0.5%) and emulsified with 40% oil using a Polytron homogenizer. Emulsion stability was determined by centrifugation and storage time, surface and interfacial tension by Du Nouy ring, particle size by integrated light scattering and overall morphology by light microscopy. When compared to the other gums in this study, fenugreek produced a very stable emulsion. Fenugreek was more efficient than other gums in lowering the interfacial free energy, its emulsion was composed of very small oil droplets (70%
Turbidimetric titration is used for the examination of pectin-casein interactions and is shown to be a simple and reliable method. It is found that the addition of pectin to casein solutions lowers the pH-value at which the casein precipitates. This effect is studied in the presence of different salts and polysaccharides and it is concluded that the stabilization of pectin-casein systems is primarily of an electrostatic nature.
Rheological properties of native corn and amaranth starches, and the changes therein on succinylation have been evaluated. The degree of substitution (DS) was varied from 0.05 to 0.20 at concentrations up to 5%. A strong shear thinning behavior was observed in all the starch pastes, as described by the power law parameters, i.e. the consistency index, K, and the flow behavior or power law index, n. The effect of concentration and DS on the apparent viscosity is described. Amaranth starch succinates showed a greater shear thinning behavior vis-à-vis corn starch succinates. The bulky hydrophilic succinate group seem to influence the rheological properties.
A new method is described for probing the structure of casein micelles and their interactions with κ-carrageen and λ-carrageenan using scanning electron microscopy (SEM). Immobilization of casein micelles at pH 6.7 to a gold substrate by means of covalent binding resulted in a homogeneous distribution of isolated, spherical casein micelles on the substrate. Detailed images of the casein micelle structure were obtained. Electron micrographs of casein micelle–carrageenan mixtures revealed aggregates, which became larger with increasing carrageenan concentration. Because of the ability of κ-carrageenan to form a gel, in contrast to λ-carrageenan, larger and more aggregates were found with κ-carrageenan at similar carrageenan concentration. Detailed images showed strands of κ-carrageenan to which casein micelles were attached, which was not observed for λ-carrageenan.
Native casein micelles are considered as an association colloid, sterically stabilized by a layer of κ-casein hairs. This hairy or furry layer, as it is traditionally called, is considered as a polyelectrolyte brush. Its stability or extension is related to the brush density (renneting), charge density (pH) along the chain, concentration of (divalent) salt ions and polarizability of the solvent (ethanol content). At lowered brush density, lowered charge density, lowered polarizability of the solvent and increased calcium level, the brush will more readily collapse on the surface of the micelle. It is then assumed that, as a result, the casein micelle loses its colloidal stability and flocculates, allowing brush collapse to be easily monitored. This simple unifying picture was checked by testing theoretical scaling relations, e.g. the relation between renneting level and pH. Results show that there is a quantitatively and qualitatively correct relation between the influence of the various parameters. A simple picture of the stability of casein micelles is presented which allows a good estimate of the influence of technological treatments on the stability of skim milk.
Changes in viscoelastic properties as a function of the wheat starch content of crab sticks from Alaska Pollock and Pacific Whiting surimi determined from transient and oscillatory measurements were studied. Based on the frequency dependence of the complex shear modulus (G∗), the two types of sticks were discriminated in terms of gel stiffness (An) and the difference (G0′−G0″) as a function of starch content. Creep and recovery tests allowed gel strength, S, to be determined from the relation modulus, G(t). This body of parameters provides an interesting method for the industrial assessment of the nominal quality of surimi and its derivatives.Overall, the tests revealed that stiffness and hardness in the product increase with increasing starch contents. Specifically, the optimum starch content for Alaska Pollock sticks was found to be 11%, above which the product becomes unacceptably hard and brittle. By contrast, the optimum starch content for Pacific Whiting sticks was 11–15%, which reflects a decreased gelling capacity of this type of surimi.
Studies have been undertaken to investigate the effect of sugars on the rheological properties of wheat starch–milk pastes. The wheat starch–milk–sugar (WMS) pastes were heated at 95 °C. The influence of sugar type and concentration, and milk fat content was deduced from the differences in the apparent viscosities and Herschel–Bulkley model parameters between these pastes. The WMS paste exhibited a typical shear-thinning behaviour. This behaviour was observed throughout the range of starch concen-tration and shear rates studied and could be attributed to stress-induced breakdown of the network structure. Sugars were found to increase the viscosity of wheat starch–milk paste in the order: glucose < sucrose < fructose. This order of the sugar effectiveness was independent of both the starch and sugar concentration, but it became more clear with increasing the starch concentration. Re-placement of skim milk by water did not change the effectiveness order of sugars on the viscosity of the starch paste. On the other hand, the wheat starch–milk paste showed higher viscosity than wheat starch–water paste. The effect of milk on the viscosity of starch paste became more pronounced with increasing the fat content of the milk.
Canavalia ensiformis native starch was acetylated, and its functional properties were evaluated. Reaction conditions assays included pH (7.0−7.5 and 8.0−8.5), acetic anhydride concentration (5 and 10%), and reaction time (30 and 60 min). Starch acetylated with 10% acetic anhydride at pH 8.0−8.5 for 30 min reached 2.34% acetyl value. Compared to native starch, these acetylated products showed an increasing pastes and gels clarity, solubility (38%), swelling power (48.4 g of water/g of starch), and viscosity (88.33 cP). The gelatinization temperature range was reduced to 67−72 °C, and retrogradation was eliminated. Keywords: Canavalia; starch; acetylation; functional properties
Differing molecular profiles of starches were developed by acid treatment of native wheat starch. Molecular weight distribution, branching, and linear chain length distribution was characterized. Starches with fewer large size amylopectin fragments, increased smaller size amylopectin fragments, decreased branch points, decreased overall sizes, and narrower linear chain length distributions, had higher initial retrogradation rates. However, all aged starch gels had similar final crystalline enthalpy levels. Different retrogradation behaviors were due to smaller size amylopectin fragments, narrowed linear chain length distribution, and decreased branching. Retrogradation behavior was modeled using classical Avrami kinetics to allow comparison with other retrogradation studies.
Starches separated from different potato cultivars were modified using two different cross-linking agents: epichlorohydrin (EPI) and phosphoryl chloride (POCl3) at different concentrations (1.0 and 2.0 g kg−1 POCl3; 2.5, 5.0 and 10 g kg−1 EPI). Differential scanning calorimetry, rheological and retrogradation measurements were performed to characterise the influence of cross-linking on the properties of potato starches. Cross-linking considerably reduced swelling power, solubility, water-binding capacity and paste clarity. The decrease became greater as the reagent concentration increased. The starches treated with 1.0 g kg−1 POCl3 exhibited exceptionally higher swelling power than their counterpart native starches. Neither cross-linking agent caused any change in morphology of the starch granules. Studies on the phase transitions associated with the gelatinisation showed significantly higher values for the onset temperature (To), peak temperature (Tp), conclusion temperature (Tc) and enthalpy of gelatinisation (ΔHgel) for the cross-linked starches than the native starches. Starches treated with both the reagents showed lower peak storage modulus (G′) and loss modulus (G″) than their native counterparts. The tendency of the starch pastes towards retrogradation increased considerably with increases in storage duration. However, the starches treated with 1 g kg−1 POCl3 exhibited much lower syneresis than the other cross-linked starches. Copyright © 2006 Society of Chemical Industry
Yogurt was formulated with gelatin; native wheat starch (NWS); and modified wheat starches (MWS) (acetylated cross-linked, hydroxypropylated, or hydroxypropylated cross-linked). Yogurt samples were evaluated for chemical (fat, total solids, pH, titratable acidity); microbiological (yeasts/molds and lactic acid bacteria); and physical (rheological, textural, color, syneresis) properties during 60 days of refrigerated storage. Yogurt formulated with NWS exhibited a significantly greater storage modulus (G′) and firmness compared with yogurts prepared with MWS. Minimal syneresis was measured in all yogurt samples. The titratable acidity of yogurt samples increased and pH decreased during storage. Yeasts/molds were not detected while lactic acid bacteria counts decreased ∼ 1 log CFU/g by day 60 in all yogurt samples. This study showed that the characteristics of yogurt formulated with NWS and gelatin were similar, so NWS may be used as an alternative stabilizer. The MWS stabilized yogurts were stable but had different consistencies than gelatin- and NWS-stabilized yogurts.
a b s t r a c t This article reviews the interactions between milk proteins and starch, with an emphasis on the physico-chemical properties, particularly the rheological and microstructural behaviour of these systems. The dairy systems considered include model mixtures made of milk, individual milk proteins and milk protein ingredients, and model dairy-based food products such as acidified skim milk gels and processed cheeses. In addition theoretical modelling of milk proteinestarch rhelogical systems are explored. Understanding how starches behave in model and applied systems will provide the dairy industry greater opportunities to produce new and difference products, at potentially lower costs. However, despite a large increase in the number of publications within this field, more study in the area is required to exploit the true potential of starchemilk protein interactions.
Large and small wheat starch granules were used for cross-linking and acetylation to determine effects of granule sizes on physicochemical properties of the modified starches. The native and cross-linked starches from the small granules showed higher phosphorus contents than did those from the large granules. However, the level of phosphate substituents in the modified starches was not significantly different between the large and small granules under the same conditions. In contrast, the large granules had a higher reactivity with acetic anhydride than did the small granules. The phosphate group cross-linked starch (CS), acetylated starch (AS) and acetylated cross-linked starch (ACS) from the large granules had lower gelatinization temperatures and higher enthalpies than those from the small granules. The paste viscosities of the CSs from the large granules decreased rapidly, whereas those of the AS or ACS increased significantly as compared with those from the small granules. The pastes of cross-linked starches from the small granules were more stable than those from the large granules, whereas the pastes of AS and ACS from the large and small granules had similar resistance to freeze-thaw treatment. Scanning electron microscopy (SEM) also showed that the small granules were less damaged after modification than the large ones. Thus, the different granule sizes resulted in different physicochemical properties of starch after modification.
In an attempt to characterize the steric stabilizing sheath around the casein micelles of bovine milk, photon correlation spectroscopy techniques have been used to measure the micellar radius on exposure to ethanolic buffers of varying pH, ionic strength and calcium concentration. It is shown that on exposure to alcohol, the stabilizing protein sheath undergoes dimensional collapse and that immediately prior to aggregation, a minimum or core radius is reached, characteristic of the diluting buffer conditions. Defining barrier thickness as the difference between the micellar radius in alcohol-free buffer and this minimum radius, the same linear relationship is observed between barrier thickness and the critical ethanol concentration required to reach the core radius and induce subsequent aggregation, whether those variations in barrier thickness were achieved by altering the pH, ionic strength or calcium level of the buffer. Considering the initial rate of response to added ethanol as a measure of barrier strength, it is observed that thicker barriers are weaker whereas thinner barriers are more resistant to collapse and hence intrinsically stronger. This paradox is qualitatively resolved by considering the stabilizing sheath to possess some of the characteristics of a weak or soft gel, whose rigidity or extent of cross-linking is influenced by the variations in buffer conditions.
The influence of cross-linked waxy maize starch on the aggregation behavior of casein micelles was investigated using a combination
of physico-chemical techniques. Milk was homogenized at two different temperatures (55 and 65 °C) and then heated at 95 °C
for 5min in a pilot scale system. The possible interactions between modified starch and milk proteins during lactic acid
fermentation were evaluated. While 1% starch did not show differences in the whey protein complexes formed during heating
compared to milk with no starch (as measured by size exclusion chromatography), a higher (2.5%) concentration of starch clearly
showed an increased amount of heat-induced whey protein aggregates. The gelation pH also increased significantly with 2.5%
starch compared to that of the control samples. The storage modulus (G′) increased with increasing levels of starch, and confocal
microscopy confirmed that the microstructure of the casein gels was altered by the presence of modified starch. Milk-starch
mixtures preheated and homogenized at 55 or 65 °C exhibited similar physico-chemical behavior during acidification. The results
suggested a lack of interaction between starch granules and casein micelles during acidification, and scanning electron microscopy
images collected with a self-assembled monolayer technique also confirmed that starch granules were not attached to milk caseins
but only embedded in the protein gel matrix.
KeywordsCasein micelles-Acid gelation-Starch-Milk
A study was made of the effect of the addition of gelatin on the microstructure of acid-heat-induced milk gels (90°C, pH=5.3) and yoghurt with and without the addition of 5% of milk solids, and a comparison was made with the microstructure of acidic milk gelatin gels obtained without heating (pH=5.3). It was seen that in the acid-heat-induced gels and in yoghurt the gelatin interacted with the network of milk proteins as a connection between the clusters formed, whereas it was the gelatin alone that was the basis of the formation of the gel when the milk did not reach the casein coagulation point (pH=5.3, unheated). The results of firmness tests indicated that the addition of 1.5% of gelatin developed fairly firm, deformable systems in all the cases studied, with a definite break point and almost total absence of syneresis. Dynamic rheology showed that the yoghurts with added gelatin exhibited more solid-like behaviour than the ones prepared without it.
Effect of some common chemical modifications such as acetylation, hydroxypropylation and cross-linking on the physico-chemical, morphological, thermal and rheological properties of starches from different botanical sources have been reviewed. The distinguishing factors that affect the efficiency of modification are the starch source, amylose to amylopectin ratio, granule morphology, and type and concentration of the modifying reagent. The extent of alteration in the starch properties reflects the resistance or the susceptibility of a starch towards different chemical modifications. Modified starches with desirable properties and degree of substitution can be prepared by critically selecting a suitable modifying agent and a native starch source.
Although traditionally associated with thickening and gelation behaviour, food hydrocolloids also influence the properties of dispersed systems through their interfacial properties. Hence, surface-active hydrocolloids may act as emulsifiers and emulsion stabilisers through adsorption of protective layers at oil–water interfaces, and interactions of hydrocolloids with emulsion droplets may affect rheology and stability with respect to aggregation and serum separation. A review of literature evidence suggests that much of the reported emulsifying capability of polysaccharides is explicable in terms of complexation or contamination with a small fraction of surface-active protein. To support this point of view, the specific cases of gum arabic, galactomannans and pectin are considered in some detail. In mixed protein+polysaccharide systems, associative electrostatic interactions can lead to coacervation or soluble complex formation depending on the nature of the biopolymers and the solution conditions (pH and ionic strength). Protein–hydrocolloid complexation at interfaces can be associated with bridging flocculation or steric stabilisation. As well as controlling rheology, the presence of a non-adsorbing hydrocolloid can affect creaming stability by inducing depletion flocculation.
Engineering design of continuous processes for liquid and semi-liquid foods involves a complex heat transfer and fluid flow coupling, which strongly depends on the rheological behaviour of fluid foods. Most of these processes are performed at temperatures above 95°C. Lack of rheological data is one major problem encountered during numerical simulation and equipment design of liquid food processing at high temperatures. Insufficient rheological studies in the literature have been conducted with food products under these conditions. This paper presents a literature review of experimental devices and methods used to obtain rheological data for starch dispersions at temperatures below and above 95°C. Results and gelatinization models from the literature are analysed and discussed.
The steady and small-deformation shear behaviors of 2–4 wt.% cross-linked waxy corn starch (CWCS) and 0.5 wt.% κ-carrageenan (κC) mixtures have been studied. In some cases κC gelation was induced by the addition of 20 mM KCl and cooling to 25°C. Rheological behavior was interpreted considering swelling-solubility as well as laser diffraction particle size and size distribution data. CWCS was chosen because it lacks amylose and its granules can swell without disruption under appropriate thermal conditions; thus the condition of particles dispersed in a continuous phase can be best fulfilled. Dispersions were heated (1.5°C/min) to 96°C, held for 10 min, then cooled (1.5°C/min) to 80°C. Steady tests were carried out at 60°C and oscillatory tests were carried out at 60 and 25°C. Only more concentrated dispersions displayed an anticlockwise up–down shear loop, which was enhanced by κC and KCl. Hysteresis disappeared with continuous shearing, and shear-thinning was observed with CWCS+κC being more viscous than CWCS+κC+KCl and CWCS. Oscillatory tests at 60°C showed that dispersions exhibited a predominantly solid-like behavior which was attenuated at lower starch concentrations and when κC and KCl were added. At 25°C, trends were similar but with slightly greater G′ and accentuated elastic character at higher starch concentrations. KCl-containing media formed gels whose rigidity depended on starch concentration. Solubility was low (<2%) and swelling increased from 25.3 g/g up to 29.6 g/g when κC was added, irrespective of starch concentration. Particle size data also showed higher swelling power in κC-containing media. Results could be interpreted in terms of two types of systems; particles suspended in a macromolecular solution and composite gels of particles embedded in a network matrix when both κC and KCl were added.
Ayran is a yoghurt drink produced in Turkey. Ayran is manufactured traditionally by adding water and salt into yoghurt or industrially by fermentation of diluted milk with water and further dilution with salt containing water after fermentation. Optimum consistency and no serum separation are desired characteristics for ayran. Use of stabilizers in traditionally manufactured ayran to prevent serum separation during storage was studied. High methoxyl pectin, guar gum, locust bean gum and gelatine at different concentrations were added to traditionally manufactured ayran and the samples were evaluated for rheological and sensory properties and serum separation during storage for 15 days at 4 °C. Guar gum provided the highest apparent viscosity and consistency index and prevented serum separation in ayran. However, guar gum provided an oily mouthfeel that was not suitable for ayran. High methoxyl pectin and gelatine did not prevent serum separation in ayran at a level of 0.25% but were effective at an increased concentration of 0.50%. Both high methoxyl pectin and gelatine affected the taste and the odor of ayran and the ayrans containing these stabilizers were found unacceptable in the sensory analysis. Locust bean gum at a level of 0.10% prevented serum separation and increased apparent viscosity without affecting the taste and the odor in ayran.
A view of the structure of the casein micelle is given. It is built of submicelles, roughly spherical aggregates of several casein molecules held together by hydrophobic bonds and salt bridges. Regions of amorphous calcium phosphate link the submicelles to each other, the ester phosphate groups form part of this colloidal phosphate. In this way, almost all regions of the casein molecules are severely restricted in mobility. The C terminal part of the κ-casein is however predominantly present as flexible “hairs” located at the outside of the micelles. There are essentially two types of submicelles, with and without (much) κ-casein. The casein micelles greatly change in properties upon lowering the pH, mostly due to dissolution of colloidal phosphate; at still lower pH, increased formation of salt bridges predominates. Temperature also has pronounced effects: upon lowering it, the micelles become more voluminous, presumably due to protruding hairs of (mainly) β-casein. Also at high temperature (>70°C), parts of the casein molecules become more flexible.
The casein micelle is an important and characteristic macromolecular assembly of mammalian biology, occurring in all milks that are examined. They form a coagulum in the stomach of the nursling, allowing the slow release of nutrients down the digestive tract, and to act as a means of transporting calcium and phosphate in a readily assimilable form from mother to young. This chapter discusses the structure and stability of bovine casein micelles. Casein micelles are spherical particles; their appearance in electron micrographs is not smooth but is likened to the surface of a raspberry. A substructure is seen in unstained thin sections of casein micelles, with regions of greater electron density dispersed evenly in a less dense matrix. When casein micelles are dissociated, spherical particles are observed with a size similar to the scale of the substructure. Casein micelles are remarkably stable structures. The appearance, substructure, size distribution, voluminosity, and dissociation of casein micelles are discussed in the chapter. The forces involved in coagulation, steric stabilization of micelles, and action of chymosin on casein micelles are also emphasized.
Pectin, a polysaccharide derived from plant cells of fruit, is commonly used as stabilizer in acidified milk drinks. To gain a better understanding of the way that pectin stabilizes these drinks, we studied the adsorption and layer thickness of pectin on casein micelles in skim milk dispersions. Dynamic light scattering was used to measure the layer thickness of adsorbed pectin onto casein micelles in situ during acidification. The results indicate that the adsorption of pectin onto casein micelles is multilayered and takes place at and below pH 5.0. Renneting, i.e., cleaving-off kappa-casein from the casein micelles, did not alter the adsorption pH. It did, however, show that pectin arrests the rennet-induced flocculation of casein micelles below pH 5.0. From the findings we concluded the attachment of pectin onto casein micelles is driven by electrosorption. Adsorption measurements confirmed the multilayered nature of the adsorption of pectin onto casein micelles. Both the adsorbed amount and the layer thickness increased with decreasing pH in the relevant range 3.5-5.0. The phase behavior of a casein micelles/pectin mixture was determined and could be explained in terms of thermodynamic incompatibility being relevant above pH 5.0 and adsorption, leading to either stabilization and bridging, being relevant below pH 5.0. The results confirm that electrosorption is the driving force for the adsorption of pectin onto casein micelles.
The interactions between exopolysaccharides produced by Lactococcus lactis ssp. cremoris JFR1 and dairy proteins (caseins and whey proteins) in fermented media (milk permeate and buttermilk) were observed using scanning electron microscopy. An immobilization technique by crosslinking was employed to bind the protein to the observation surface, so that a washing step could be performed to remove noninteracting material. The use of this novel technique allowed us, for the first time, to confirm that the exopolysaccharide molecules interact with dairy proteins. Exopolysaccharides appear as filament strands attached to the protein aggregates and to the bacterial cells. This new sample preparation technique proved to be very valuable for observing molecular interactions in fermented media.