The effect of high pressure homogenization on the improvement of the stability hydroxypropyl cellulose (HPC) and micellar casein was investigated. HPC with two molecular weights (80 and 1150 kDa) and micellar casein were mixed in water to a concentration leading to phase separation (0.45% w/v HPC and 3% w/v casein) and immediately subjected to high pressure homogenization ranging from 0 to 300 MPa, in 100 MPa increments. The various dispersions were evaluated for stability, particle size, turbidity, protein content, and viscosity over a period of two weeks and Scanning Transmission Electron Microscopy (STEM) at the end of the storage period. The stability of casein-HPC complexes was enhanced with the increasing homogenization pressure, especially for the complex containing high molecular weight HPC. The apparent particle size of complexes was reduced from ~200nm to ~130nm when using 300 MPa, corresponding to the sharp decrease of absorbance when compared to the non-homogenized controls. High pressure homogenization reduced the viscosity of HPC-casein complexes regardless of the molecular weight of HPC and STEM imagines revealed aggregates consistent with nano-scale protein polysaccharide interactions.
Polymethoxyflavones (PMFs) extracted from citrus peel exhibit potent anti-cancer activity, but are highly hydrophobic molecules with poor solubility in both water and oil at ambient and body temperature, which limits their bioavailability. The possibility of encapsulating PMFs within nanoemulsion-based delivery systems to facilitate their application in nutraceutical and pharmaceutical products was investigated. The influence of oil type (corn oil, MCT, orange oil), emulsifier type (β-lactoglobulin, lyso-lecithin, Tween, and DTAB), and neutral cosolvents (glycerol and ethanol) on the formation and stability of PMF-loaded nanoemulsions was examined. Nanoemulsions (r < 100 nm) could be formed using high pressure homogenization for all emulsifier types, except DTAB. Lipid droplet charge could be altered from highly cationic (DTAB), to near neutral (Tween), to highly anionic (β-lactoglobulin, lyso-lecithin) by varying emulsifier type. PMF crystals formed in all nanoemulsions after preparation, which had a tendency to sediment during storage. The size, morphology, and aggregation of PMF crystals depended on preparation method, emulsifier type, oil type, and cosolvent addition. These results have important implications for the development of delivery systems for bioactive components that have poor oil and water solubility at application temperatures.
Nutraceuticals provide health benefits, especially for the prevention and treatment of chronic diseases such as diabetes, obesity, cardiovascular disease and cancer. Their incorporation in food supplements, functional foods and medicinal foods is a major technological challenge due to lower water solubility, instability during processing and storage conditions. Carriers that can effectively overcome these predicaments and protect them during product development, consumption and delivery are in high demand. Toward this end, our research approach is to entrap nutraceuticals in the ordered networks of hydrocolloids. We have examined the effect cations in regulating the encapsulated amounts and release characteristics. Iota-carrageenan and eugenol have been chosen as models of hydrocolloid and nutraceutical, respectively, in the presence of Na and Ca ions. The results suggest that carrageenan maintains its network organization even after encapsulating the eugenol molecules. Increased eugenol amounts are found in the Na carrageenan complex compared to the Ca complex, and the release rate is faster from the former but it is more controlled from the latter. These differences highlight the vital role of cations on the encapsulation efficiency and release profiles of hydrocolloid-based nutraceutical carriers. The outcome offers an elegant opportunity for developing novel and value-added food systems employing low-in-cost, nontoxic and heavily consumed food grade hydrocolloids.
A particulate form of xanthan gum was prepared by extrusion cooking. The temperature dependence of the viscosity of this form shows similarities to starch with an increase in viscosity to a maximum with increasing temperature as a result of the swelling of the particles. The rheology and mixing behaviour with water of the particulate and conventional molecular forms of xanthan were compared with a modified starch. The particulate xanthan products mixed rapidly with water in a similar way to ungelatinised starch, whereas conventional molecular xanthan systems mixed poorly. Using an experienced sensory panel, model tomato products thickened with the three systems were compared at equal shear viscosities. The panel could not discriminate between the tomato flavour of the three products, but found that the xanthan products were perceived as being significantly thicker. These observations were consistent with previous work. Salt perception for both xanthan products was poorer than for the starch thickened systems. A hypothesis to explain why xanthan does not fit into the previously postulated link between mixing and perception is presented.
The influence of high pressure (HP) treatment (200–600 MPa) on the emulsifying activity index (EAI) and emulsifying stability index (ESI) on the 7S and 11S globulins and soya protein isolate (SPI) at pHs 7.5 and 6.5, at different concentrations (0.25–0.75%) was studied. Solubility and surface hydrophobicity were used as indices of the degree of denaturation caused by HP. 7S showed the highest EAI and surface hydrophobicity after treatment at 400 MPa, whereas 11S showed its highest EAI and surface hydrophobicity after treatment at 200 MPa. No significant correlation (P>0.05) was found between solubility and EAI or hydrophobicity. SPI showed the optimum value of EAI after treatment at 400 MPa although its surface hydrophobicity was low. It is suggested that pressure at 400 MPa dissociated the 7S of the SPI into partially or totally denatured monomers that enhanced the surface activity but at the same time, the unfolding of the polypeptides of the 11S within the hexamer led to aggregation, negatively affecting the surface hydrophobicity of the SPI. The ESI values for the non-treated samples of SPI, 7S and 11S were higher at lower concentrations. At the same pH and concentration, the ESI decreased with increasing HP, except for the 7S at pH 7.5 and a protein concentration of 0.75%.
The influence of ι-carrageenan (ι-CAR) on the solution, interfacial and emulsifying properties of 11S globulin Viciafaba at low ionic strength and pH 8 has been investigated before and after high-pressure processing at 200 MPa for 20 min. The total calorimetric enthalpy (ΔH) and size exclusion chromatography studies for the pure 11S indicate that there is subunit dissociation and extensive aggregation of the protein during or following treatment. Under the same treatment conditions, 1-anilinonaphthalene-8-sulphonate (ANS) data has shown increased protein surface hydrophobicity. Pressure treatment of 11S gives much lower values of the surface tension, and apparent surface shear rheology experiments show that the molecules in the film adsorbed from the pressurised 11S are much more strongly interacting than those adsorbed from the native 11S. However, emulsions prepared with pressure processed 11S give substantially bigger droplets than those made with the untreated pure protein. Addition of ι-CAR to 11S reduces the denaturation temperature (Tm), the ΔH value, and protein surface hydrophobicity. Size exclusion chromatography at low ionic strength is indicative of complex formation. Tension measurements at the air–water interface are also consistent with the presence of a complex. Emulsions made with the simple 1:0.33 mixture of 11S+ι-CAR give emulsions with smaller droplets and pressure processing of the biopolymer mixture leads to emulsions with even smaller droplets. The presence of ι-CAR at low ionic strength appears to protect the globulin against pressure-induced aggregation.
The influence of dextran on the interfacial pressure of adsorbing layers of legumin (11S globulin vicia faba) at the planar n-decane/aqueous solution interface was studied under conditions of thermodynamic compatibility and incompatibility between these biopolymers. The thermodynamic incompatibility of legumin with dextran in the bulk aqueous solution leads to an increase in the interfacial pressure of the adsorbing layers of legumin. This effect may be caused by the excluded volume effect between molecules of the biopolymers in the bulk aqueous solution. Opposite effects are observed under conditions of thermodynamic compatibility between these biopolymers. In the latter case they may be related to the intensification of thermodynamically favourable interactions of legumin with dextran molecules in the bulk aqueous solution.
Fourier transform infrared (FTIR) method was used to study the secondary structures of 7S and 11S globulins from soybean proteins using aqueous buffer and reverse micelles extraction method for the first time. The Fourier second derivative was applied to all spectra, revealing that the amideband of 7S and 11S globulins with two extraction methods consisted of eight bands. The I band frequencies were assigned to α-helix, β-sheet, unordered and turn structure. The second derivative spectra of 7S and 11S globulins had been shifted with reverse micellar extraction method compared with their spectra with aqueous buffer extraction method. The relative amount of different structure of 7S and 11S globulins could be estimated through accurate measurement of the band intensities. The results indicated that the percentage of 7S globulin α-helix and β-sheet, turn structures decreased with the reverse micelles extraction (7S globulin: 14.5% α-helix, 45.6% β-sheet, 14.4% unordered, 23.8% turn; 11S globulin: 17.0% α-helix, 47.3% β-sheet, 16.5% unordered, 19.3% turn), compared with 7S (16.5% α-helix, 47.6% β-sheet, 35.9% turn) and 11S (17.0% α-helix, 47.3% β-sheet, 35.8% turn) globulins by the aqueous buffer extraction, while the percentage of 11S globulin α-helix and β-sheet structures did not change. The percentage of unordered structure was 14.4 and 16.5, respectively. The amount change of these substructures might affect functional properties of 7S and 11S globulins.
This paper presents a study of the effect of aroma compound (hexyl acetate, HxAc) on thermodynamic properties of legumin (11S globulin from broad beans) in an aqueous medium (protein conformational stability and protein–protein interactions) by a combination of gas–liquid chromatography, differential scanning microcalorimetry, static light scattering and sedimentation velocity analysis. The aqueous phase at the ionic strength of 0.05 mol dm−3 was buffered at pH 7.2 and 3.0. The conformational stability of the native 11S globulin (pH 7.2) was maximum at the point of saturation of the protein molecules with the aroma ligand, which was determined from the binding isotherm. At pH 3.0, the protein conformational stability did not change over the same concentration range of HxAc, i.e. where the protein binding capacity for HxAc was studied. As a result of the binding of HxAc with 11S globulin the thermodynamic affinity between protein molecules in an aqueous medium increased in the case of the native protein, remained unchanged for the acid-denatured protein and reduced in the case of the heat-denatured protein at the same concentration of HxAc in the system. An excess of concentration of HxAc in the solutions above the saturation level for the protein, according to the binding isotherm, led to protein aggregation in an aqueous medium owing to spontaneous protein unfolding.
The effect of pH on the thermodynamic properties of the mixed solution of the two different globular proteins, oligomeric globular protein-11S globulin andmonomeric globular protein-ovalbumin, has been studied. Thermodynamic incompatibility of the proteins was observed at pH 7.0 and 7.8, which are above the proteins' isoelectric points. Thermodynamic properties of the system were studied by phase analysis from moderate to high concentration and by light scattering on dilute solutions below the separation threshold. The rise of the concentration region of the protein immiscibility in the mixed protein solution was observed under a pH change from pH 7.8 to 7.0. Comparison of the alteration of the character of the interactions between all components of the solution with pH variation shows that the basic reason for the rise in protein immiscibility with pH decrease (from 7.8 to 7.0) is intensification of the self-association of the mixed proteins, mainly of 11S globulin. It was established that the forces of electrostatic repulsion between both the similar and different protein molecules play a key role in the phase separation of the mixed protein solutions at pH 7.8. In contrast, the results obtained exhibit the determining role of the attractive forces acting between protein molecules and dictating features of the phase state of the mixed protein solution at pH 7.0.
The influence of heat (up to 80°C for 2 min) and high-pressure (up to 250 MPa for 20 min) on the emulsifying properties of 11S globulin Vicia faba at pH 8.0 has been investigated for systems containing the sulphated polysaccharides ι-carrageenan (ι-CAR) and κ-carrageenan (κ-CAR). The emulsions (0.5 wt% 11S, 20 vol% n-tetradecane) made with heated or high-pressure treated 11S were found to give substantially larger droplets than those made with the native protein. Visual creaming behaviour has been monitored as a function of storage time. There was a consistent trend of decreasing emulsifying efficiency and emulsion stability with increase in treatment temperature or pressure. Addition of ι-CAR or κ-CAR (3:3–7:1 by weight) to the native protein at low ionic strength led to smaller droplets whose size decreased with increase in polysaccharide concentration and extent of high-pressure treatment (up to 200 MPa). Thermally treated biopolymer mixtures gave emulsions with droplets that did not significantly change with increase in temperature. In all cases, the presence of ι-CAR led to a significant improvement in creaming stability. However, the presence of κ-CAR in untreated and thermally treated (<75°C) mixtures gave rapid serum separation probably due to depletion flocculation. Of the two polysaccharides studied, ι-CAR gave the smallest droplets in fresh emulsions and the best stability with respect to visual creaming behaviour. The observations for 11S alone can be interpreted in terms of pressure or thermally induced unfolding of the protein, which results in a decrease in emulsion efficiency due to dissociation of subunits or protein aggregation. It appears that the strength of interaction of 11S with ι- or κ-CAR is dependent on the charge density on the polysaccharide. The presence of interacting polysaccharide in the heated and high-pressure processed samples seems to inhibit the formation of aggregates. High-pressure treatment of the mixed biopolymer solutions in the presence of sodium chloride (>0.01 M) destabilises the emulsion, and so the protective effect of polysaccharide is lost.
Oil-in-water emulsions containing 30% soya oil and various concentrations of sodium caseinate were prepared in a two-stage valve homogenizer. The emulsions were sealed in glass bottles and then heated at 121°C for 15 min in an autoclave. In some experiments, the caseinate solutions were heated at 121°C for 15 min first, mixed with soya oil (to give 30% oil in the final emulsion) and then homogenized. Heat treatment (121°C for 15 min) of either sodium caseinate emulsions or sodium caseinate solutions prior to emulsion formation, at all caseinate concentrations used, resulted in an increase in surface coverage, an increase in creaming stability and a change in the proportions of individual caseins at the droplet surface. Heat treatment of sodium caseinate solutions resulted in the formation of several new peptides, due to protein degradation, as well as polymerization of casein molecules, as revealed by SDS–PAGE. Both the polymerized caseinate material and degradation products were adsorbed efficiently during emulsification; the degradation products were more readily adsorbed than the parent protein. Experiments on heated emulsions indicated that the adsorbed caseinate molecules were more susceptible to degradation during heating than those in solution.
The crystalline microstructure and polymorphism of C-type starch from Chinese yam were evaluated by scanning electron microscope (SEM), 13C cross-polarization magic-angle spinning NMR (13C CP/MAS NMR) and powder X-ray diffraction (XRD) technique and acid hydrolysis method. Morphological changes during acid hydrolysis showed that the amorphous or the less crystalline areas were essentially located at the center part of C-type starch granules whereas the semi-crystalline and amorphous growth rings were found mainly in the outer part of the granules. 13C CP/MAS NMR and XRD results revealed that B-type allomorph was hydrolyzed more rapidly than A-type one. The amorphous or less crystalline areas were predominantly composed of B-allomorph whereas the outer semi-crystalline and amorphous growth rings were mostly composed of A-type allomorph. The A- and B-type allomorph coexisted in the individual C-type starch granule. B-type allomorph basically existed at the center part of the granules which was surrounded by the A-type allomorph in the peripheral part of granules.
A screening was made among 18 novel strains of Xanthomonas campestris pv pruni. Yields, viscosity and chromatographic patterns of the biopolymers synthesized in a conventional medium (PM II), were analyzed. Yields varied from 2.3 to 8.3 g l−1. Viscosities of 3% (w/v) aqueous solutions at 25, 45 and 65°C, were determined at 6, 12, 30 and 60 rpm. All biopolymers had pseudoplastic behavior. The biopolymers showed three distinct viscosity patterns when temperature increased: no variation, decrease and increase. Polymers that maintained or increased their viscosity had higher mannose concentrations. Strain 06 was chosen for further studies because it showed a higher viscosity at 6 rpm, 26,000 mPa s at 25°C and 27,000 mPa s at 65°C, and a yield of 4.0 g l−1. The influence of the concentration of biopolymer (1 and 2%) and temperature (25, 45 and 65°C) in the viscosity was also determined. A small increase in viscosity when the temperature was raised was observed at both concentrations. Finally, the influence of fermentation time (24–96 h) on yield, viscosity and chemical composition of the biopolymers, was determined. The biopolymer obtained after 24 h of fermentation showed the higher viscosity, but the highest yield was obtained at 72 h. The biopolymer produced by strain 06 after 48 h of incubation showed similar viscosity and rheological behavior to commercial xanthan.
The emulsification properties of an isolate of β-lactoglobulin (β-LGI) and a whey protein fraction (WPF) of reconstituted skim milk were studied in a milk-based environment containing anhydrous milk fat at 4 and 18% by modifying protein concentration. At a similar protein-to-fat ratio, fat content per se was not associated with changes in initial particle size, but was related to stability during storage. In the more concentrated emulsions, creaming was inhibited and no longer affected time-dependent aggregation of fat globules, except under the most extreme conditions (i.e. in the presence of a higher proportion of α-lactalbumin, at high initial particle size and at high storage temperature). However, aggregation was enhanced by the presence of a higher proportion of α-lactalbumin, which was detrimental to physical stability.Using laser desorption mass spectroscopy, the molecular mass of a significant proportion of WPFs whey protein was observed to be increased, possibly as a result of lactolation. In addition, β-LGI contained some calcium, which slightly increased the concentration of calcium in emulsions made with β-LGI. These differences in molecular mass and calcium concentration did not enhance the stability of emulsions prepared with β-LGI over that of those prepared with WPF.
The structure of a water soluble arabinogalactan isolated from gum ghatti (Gatifolia SD) was elucidated by methylation analysis and 2D NMR spectroscopy. The arabinogalactan fraction (F80) was obtained by a sequential ethanol precipitation of gum ghatti (Gatifolia SD). Methylation and GC–MS analysis indicated that F80 was a highly branched polysaccharide; the terminal sugar residues were about 40.8% of the total sugars. The majority of the terminal units were α-l-Araf, with small amounts of T-GlcpA, T-Arap, T-Rhap and T-Galp. About 14.2% of the total sugar residues were →6)-β-d-Galp-(1→ branched at 3rd and 4th positions. The linear portion of the arabinogalactan was composed of →4)-GlcpA(1→, →6)-Galp(1→ and →2)-l-Araf-(1→ linkages. Based on the results from methylation analysis, 1D (1H, 13C) and 2D (COSY, TOCSY, HMQC and HMBC) NMR spectroscopy, the structure of F80 was proposed as follows:R is one of the following groups: →3)-β-d-Galp-(1→, →5)-β-d-Araf-(1→, →2,3-Manp1→, T-α-l-Araf 1→, T-GlcpA1→ and T-l-Arap 1→. Galactose has the -β-D configuration, while the arabinose and rhamnose are in the α-l form.Graphical abstract
It was demonstrated that macroscopic structural changes of polysaccharide chains, such as random coil–helix transition and aggregation of helices, accompanied with the sol–gel and the gel–sol transition can be monitored by numerically analyzing the temperature dependence of the observed water proton spin–spin relaxation time (T2obs) modified by the chemical exchange between water proton and labile proton on the chain. According to the numerical analysis of T2obs, typical profiles of T2obs against the temperature were simulated with various parameters of the relaxation time (T2i) and the mean residence time (τi) of water and the labile protons on the random coil and the ordered chain as well as the activation energy (Ei,Eex,i) for the motion and the chemical exchange of the respective proton. The difference of structural change of kappa- , iota- , and lambda-carrageenan aqueous systems in the cooling and the heating process was analyzed. In conclusion, (1) the characteristic profile of the temperature dependence of T2obs, commonly observed in the temperature-induced gelling process, is attributable to the variation of fraction of the ordered chain and the relative rate of chemical exchange to the relaxation rate of labile protons on polysaccharide (1/T2p); (2) the loose aggregated or associated structure is detected for iota-carrageenan system; and (3) the thermally stable junction zones formed by well aggregated helices of kappa-carrageenan in the gel state provokes a thermal hysteresis in the temperature-induced structural change (experimentally, in T2obs). It is clarified by the numerical simulation that the aggregated helices formed during further cooling down to the temperature below Tsg results in the T2obs shifts to a longer value in the heating process as compared with that in the cooling process.
The gelling properties of pectins are known not only to be closely related to the degree of esterification (DE), but also to the distribution of the ester groups. In this study we have examined an experimentally designed series of pectins originating from the same mother pectin and deesterified using combinations of two different enzymatic mechanisms. The DE and distribution patterns of methyl ester groups have been analyzed using high-resolution (HR) 1H nuclear magnetic resonance (NMR) spectroscopy on pectin solutions. Quantitative calibration models using partial least squares (PLS) regression were developed with the ability to predict DE as well as the specific enzyme treatment, expressed as amount of ester groups removed with random and block enzyme, respectively. NMR spectroscopy was able to distinguish between enzyme treatments in simple classification by principal component analysis (PCA). This was due to the spatial structure of pectin together with the methyl ester distribution. Nuclear Overhauser effect spectroscopy (NOESY) experiments confirmed all the general assignments with the expected nuclear Overhauser effect (NOE) correlations. Degree of random deesterification (R) was better predicted than the degree of block deesterification (B). The calibration models for prediction of R obtained on extended inverted signal correction (EISC) processed data gave a root mean square error (RMSE) of cross-validation (CV) of 2%p with 4 PLS components (latent variables, LV) and a correlation coefficient (r) of 0.98. Spectral variable selection using interval PLS (iPLS) was shown to be valuable, as all the calibration models were improved.
23Na NMR molecular mobility studies were performed to investigate the interaction between sodium ions and various hydrocolloid—water systems as affected by the nature of the hydrocolloid (ionic and non-ionic) and the concentration of added NaCl (0–5000 mg/100 ml). At low amounts of added NaCl (20–100 mg/100 ml) the transverse relaxation rates (R2) for the ionic gums, kappa-carrageenan and xanthan, rapidly decreased and were larger than those for the non-ionic gums, guar and locust bean. At higher concentrations of added NaCl (>100 mg/100 ml), R2 for the ionic gums gradually levelled off, approaching the R2 values for the non-ionic gums. For the xanthan-water system, the R2 for the endogenous Na+ concentration and very low added NaCl concentrations (<15 mg/100 ml) were also measured. This research suggests that gum type, NaCl and endogenous cation concentrations affect the binding of Na+ to the gums.
Gelatinization behavior of starch in an aqueous system was studied in the presence or absence of various guar gum samples with different molecular weights in order to clarify the difference in functions of each guar to starch. Some native corn starches with different amylose/amylopectin ratios were used to clarify which fraction of starch the gums act on. Weight-average molecular weight Mw of the guar samples ranged from 4.7×105 to 34.6×105 g/mol, whereas z-average root-mean-square radius of gyration Rg ranged between 82 and 233 nm from static light-scattering technique. Relationship between Mw and Rg was expressed by the Flory exponent of 0.503. Also, intrinsic viscosity [η] of the guar samples in aqueous solution was in good agreement with Mw determined, and relationship between Mw and [η] was expressed by the Mark–Houwink–Sakurada exponent of 0.517. Gelatinization behavior of starch/guar system was investigated from its viscosity profiles. Guars with Mw values higher than 12.2×105 g/mol shifted the onset of viscosity increase for the system to lower temperatures and increased its peak viscosity upon heating at a relatively low starch concentration (e.g. 5 w/v%). The earlier onset of viscosity increase was independent of Mw of guar, while the increase in peak viscosity was dependent on its Mw. These guars shifted the onset of viscosity increase for the system upward, on the contrary, at a relatively high starch concentration (e.g. 15%). Interaction between guar and starch components, amylose and amylopectin, was hypothesized as one of the factors to govern the gelatinization behavior of starch.
Retrogradation behavior of corn starch in an aqueous system was studied in the presence or absence of various guar gum samples with different molecular weights. Dynamic mechanical loss tangent for starch system with 26% amylose (5 w/v%) was increased by the addition of guar (0.5%) after storage at 4 °C for 24 h, which indicated the reduction of gelled fraction in the system, leading to the retardation of short-term retrogradation of starch. This rheological change of the system related to the amount of amylose leached out the starch granules during gelatinization. The higher the molecular weight of guar, the lower the amount of amylose leached, but this effect of guar became less dependent on its molecular weight at above 15.0×105 g/mol. The rate constant determined from the relationship between storage time (for 14 days at 4 °C) and creep compliance for the starch system (15% starch) was decreased in the presence of guar (0.5%), suggesting the retardation of long-term retrogradation of starch. This effect of guar became marked at above 30.0×105 g/mol, which was apparently higher than the critical molecular weight value determined from short-term retrogradation. Syneresis for the starch system (5% starch) was increased adversely by the addition of guar (0.5%) with relatively low molecular weight values (e.g. <5.0×105 g/mol) after storage at 4 °C for 14 days, suggesting the promotion of long-term retrogradation. Functions of guar on the retrogradation behavior of starch were hypothesized considering interactions between guar and starch components; amylose and amylopectin.
Generalized 2D correlation spectroscopy (COS) has been applied to FTIR spectra of porcine plasma proteins to elucidate the sequence of events leading to pH- and/or thermal-induced protein unfolding and aggregation. Changes in the amide I′ region of the infrared spectra (in the pH range between 7.5 and 4.5, at 0.5 pH intervals) at 30 °C were especially evident as the pH approached the pI of serum albumin (4.8), with the globulin fraction in the plasma proteins undergoing denaturation prior to serum albumin. The effect of increasing temperature (from 30 to 90 °C, in increments of 5 °C) on the secondary structure of the plasma proteins at pHs in the range of 7.5–6.0 revealed that a decrease in alpha-helical structures is taken place previously to diminish native beta-sheets. So, the overall results of this study demonstrate that serum albumin and the globulin fraction differ in their sensitivity to pH and temperature.
Deuterium-labelled (methyl-d3) pectin was prepared by esterifying a lemon peel pectin with methanol-d4. A pure powder sample and multicomponent model confectioneries containing the labelled pectin and various amounts of water were studied by solid-state 2H NMR spectroscopy. In the pure sample the broad 2H NMR lineshape indicates that the only fast motion occurring on the NMR timescale is reorientation of the methyl-d3 group about its C3 axis. In contrast, in systems of 50% water content the 2H NMR lineshape is much narrower, indicating significant motional averaging. As the percentage water in the confectionery systems is reduced to <40% the main effect is the appearance of a broad component in the spectrum associated with a more static motional environment. As the water content decreases further the proportion of labelled pectin in this region increases and the amplitude of the motions decreases, until for systems of <10% water content motions are now slow on the NMR timescale, except for the methyl-d3 group reorientation about its C3 axis, and 2H NMR lineshapes are identical to those observed in the pure powder sample. The evolution of the two component lineshape indicates that the removal of successive amounts of water does not simply ‘stiffen’ the entire system but rather initially restricts motion in certain regions and eventually ‘crystallizes’ distinct domains within the sample.
Oat and barley β-glucans were isolated from their respective concentrates that were prepared through a novel technology, containing total phosphorus at 0.920 and 0.170%, w/w, respectively. The highest purity of oat and barley β-glucans achieved was 97 and 90%, w/w (db), respectively. Purified oat and barley β-glucans contained 21.8 and 54.1%, w/w, respectively, of the total phosphorus present in the corresponding β-glucan concentrates. On a weight basis, the total phosphorus content in purified oat and barley β-glucans was 0.201 (degree of substitution (DS)=0.011) and 0.092% (DS=0.005), respectively. 31P NMR of both types of β-glucans showed the presence of inner C-6 carbon bound phosphomonoesters and an unknown form of phosphorus, possibly phospholipids and/or phosphoproteins. In addition to these phosphorus forms, barley β-glucan sample contained pyrophosphate for which the origin was unknown. Although a substantial amount of phytate phosphorus (0.745 and 0.103%, w/w, for oat and barley, respectively) was present in both types of β-glucan concentrates, this form of phosphorus was absent in the purified β-glucan as evidenced by 31P NMR data. Aqueous extractability of oat β-glucan from purified sample at 37 °C was 6.6-fold higher than that of barley β-glucan at the same temperature. This may partly be attributed to the presence of more (46%) negatively charged phosphorus substitution in oat β-glucan than in barley.
The heat denaturation and aggregation behaviour of β-lactoglobulin (β-LG) enriched WPI was investigated at pH 4.0 and 7.0 in the presence of arginine HCl, NaCl and GdnHCl using differential scanning calorimetry (DSC) and dynamic light scattering (DLS). Beside the classical endothermic signal attributed to protein heat denaturation, DSC thermograms displayed appearance of an additional exothermic peak in the presence of cosolute. Using in situ DLS, it was shown that the appearance of the exothermic peaks is linked to protein aggregation, in particular to a strong increase in aggregate size. Upon increased cosolute concentration at pH 4.0 the exothermic peak occurred at temperatures lower than the actual denaturation peak (∼85 °C). At this pH, negatively charged chloride anions interact with β-LG leading to charge screening and physical aggregation. At pH 7.0, exothermic peaks appeared at higher temperatures than the denaturation peak (∼75 °C). Upon increased cosolute concentration the exothermic peak was shifted to lower temperatures, indicating protein destabilisation in the presence of cosolutes. Charge screening of β-LG by the positively charged cations (arginine, Na and guanidinium) reduced repulsion forces and promoted aggregation.