Rheological properties of reduced lactose whey dispersions

The rheological behaviour of reduced lactose whey (RLW) dispersions of several different types of whey products was investigated with dynamic small amplitude oscillatory (SAOS) rheometry and rotational rheometry. The different aggregation states of the proteins were measured by using size-exclusion chromatography (SEC) with multiangle laser light scattering (MALLS). Differences in the mineral content (especially calcium and phosphate) of the RLW samples contributed to their different rheological properties. Calcium phosphate/whey protein aggregates were probably formed when the mineral content increased, resulting in an increase in the size of the aggregates and higher viscosity. These complexes were also more sensitive to heating.     

Modulation of rheological properties by heat-induced aggregation of whey protein solution

Heat-induced protein aggregation at low protein concentrations generally leads to higher viscosities. We here report that aggregated protein can yield weaker gels than those from native protein at the same concentration. Aggregated protein was produced by heating a solution of whey protein isolate (WPI) at 3% and 9% w/w. The higher protein concentration resulted in a larger aggregate size and a higher intrinsic viscosity. The protein fraction in native WPI had the smallest size and the lowest intrinsic viscosity. The same trend was observed for the shear viscosity after concentrating the suspensions containing aggregates to around 15% w/w. Suspensions containing aggregates that were produced from a higher concentration possessed a higher viscosity. After reheating the concentrated suspensions, the suspension from the 9% w/w aggregate system produced the weakest gel, followed by the one from 3% w/w, while the native WPI yielded the strongest gel. Reactivity of the aggregates was also an important factor that influenced the resulting gel properties. We conclude that aggregation of whey protein solution is a feasible route to manipulate the gel strength of concentrated protein systems, without having to alter the concentration of the protein.     

Physicochemical properties of whey protein isolate stabilized oil-in-water emulsions when mixed with flaxseed gum at neutral pH

Concentrations ranging from 0% to 0.33% (w/v) of gum (Emerson and McDuff) were added to the emulsions at pH 7. Particle size distribution, viscosity, ζ-potential, microstructure, and phase separation kinetics of the emulsions were observed. Both polysaccharides and protein coated droplets are negatively charged at this pH, as shown by ζ-potential measurements. At all the concentrations tested, the addition of gum did not affect significantly (p < 0.05) the apparent diameter of the emulsion droplets. At low concentrations (gum  0.075% (w/v)), no visual phase separation was observed and the emulsion showed a Newtonian behaviour. However, at concentrations above the critical concentration of gum, depletion flocculation occurred: when 0.1 flaxseed gum was present, there was visual phase separation over time and the emulsion exhibited shear-thinning behaviour. These results demonstrate that flaxseed gum is a non-interacting polysaccharide at neutral pH; it could then be employed to strengthen the nutritional value of some milk-based drinks, but at limited concentrations.     

Study on the rheological properties of heat-induced whey protein isolate-dextran conjugate gel

Effect of glycosylation on the rheological properties of whey protein isolate (WPI) during the heat-induced gelation process was evaluated. Significant changes in browning intensity, free amino groups content and SDS-PAGE profile showed that the conjugate of WPI and dextran (150 kDa) was successfully prepared using the traditional dry-heating treatment. For the conjugate, during the heating and cooling cycle, the curves of G′ and G″ were considerably shifted to lower values and their shapes varied comparing to the corresponding spectra of initial WPI and WPI + dextran mixture. After holding at 25 °C, G' reached a value of about 2200 Pa, only a tenth of the value that obtained in the initial WPI gel. Moreover, frequency sweep measurements revealed that the stiffness of gel was greatly reduced in the conjugate, although a typical elastic gel was still formed. All data showed that the rheological properties of thermal gelation could be modified upon the covalent attachment of dextran.     

Influence of biopolymer emulsifier type on formation and stability of rice bran oil-in-water emulsions: whey protein, gum arabic, and modified starch

Rice bran oil (RBO) is used in foods, cosmetics, and pharmaceuticals due to its desirable health, flavor, and functional attributes. We investigated the effects of biopolymer emulsifier type and environmental stresses on the stability of RBO emulsions. Oil-in-water emulsions (5% RBO, 10 mM citrate buffer) stabilized by whey protein isolate (WPI), gum arabic (GA), or modified starch (MS) were prepared using high-pressure homogenization. The new MS used had a higher number of octenyl succinic anhydride (OSA) groups per starch molecule than conventional MS. The droplet diameters produced by WPI and MS were considerably smaller (d < 300 nm) than those produced by GA (d > 1000 nm). The influence of pH (3 to 8), ionic strength (0 to 500 mM NaCl), and thermal treatment (30 to 90 °C) on the physical stability of the emulsions was examined. Extensive droplet aggregation occurred in WPI-stabilized emulsions around their isoelectric point (4 < pH < 6), at high salt (> 200 mM, pH 7), and at high temperatures (>70 °C, pH 7, 150 mM NaCl), which was attributed to changes in electrostatic and hydrophobic interactions between droplets. There was little effect of pH, ionic strength, and temperature on emulsions stabilized by GA or MS, which was attributed to strong steric stabilization. In summary: WPI produced small droplets at low concentrations, but they had poor stability to environmental stress; GA produced large droplets and needed high concentrations, but they had good stability to stress; new MS produced small droplets at low concentrations, with good stability to stress. Practical Application: This study showed that stable rice bran oil-in-water emulsions can be formed using biopolymer emulsifiers. These emulsions could be used to incorporate RBO into a wide range of food products. We compared the relative performance of whey protein, GA, and a new MS at forming and stabilizing the emulsions. The new OSA MS was capable of forming small stable droplets at relatively low concentrations.     

Effect of protein composition on the rheological properties of acid-induced whey protein gels

Protein dispersions with different ratios of α-lactalbumin to β-lactoglobulin were heat-denatured at pH 7.5 and then acidified with glucono-δ-lactone to form gels at room temperature. Heat treatment induced the formation of whey protein polymers with reactive thiol group concentrations ranging from 1 to 50 μmol/g, depending on protein composition. During acidification, the first sign of aggregation occurred when the zeta potential reached −18.2 mV. Increasing the proportion of α-lactalbumin in the polymer dispersions resulted in more turbid gels characterized by an open microstructure. Elastic and viscous moduli were reduced, while the relaxation coefficient and the stress decay rate constants were increased by raising the proportion of α-lactalbumin in the gel. After one week of storage at 5 °C, gel hardness increased by 12%. The effect of protein composition on acid-induced gelation of whey protein is discussed in relation to the availability and reactivity of thiol groups during gel formation and storage.     

Effect of ultrasonic treatment on the rheological properties and particle size of gum tragacanth dispersions from different species

Dispersions of different species of gum tragacanth were sonicated at a frequency of 24 kHz with a total nominal output power of 200 W for different time intervals (0, 7, 15, 45 and 90 s). Various species behave differently under sonication, which is related to structural differences in these species. In the case of Astragaslus compactus and A. rahensus dispersions, as the sonication time increased, the viscosity and particle size of the dispersions decreased, just as in gum Arabic solutions. However, A. gossypinus gum behaved differently compared to the other species. At early stages of sonication (up to 15 s), the viscosity of the dispersions increased sharply and reached its maximum value (106.04 mPa s) as the particle size increased slightly to 275.69 μm. Continuing sonication led to a decrease in the viscosity of the dispersions, though the particle size did not show any changes. This behaviour is thought to be due to the rupture and aggregation of particles.     

Rheological properties of whey protein isolate stabilized emulsions with pectin and guar gum

Dynamic oscillatory and steady-shear rheological tests were carried out to evaluate the rheological properties of whey protein isolate (WPI) stabilized emulsions with and without hydrocolloids (pectin and guar gum) at pH 7.0. Viscosity and also consistency index of emulsions increased with hydrocolloid concentration. At γ = 20 s⁻¹, the value of viscosity of the emulsion with 0.5% (w/v) pectin was about fivefold higher than that of the emulsion without pectin. Flow curves were analyzed using power law model through a fitting procedure. Flow behaviour index of all emulsions except for containing 0.5% (w/v) guar gum was approximately in the range of 0.9–1.0, which corresponds to near-Newtonian behaviour. The shear thinning behaviour of emulsions containing 0.5% (w/w) guar gum was confirmed by flow behaviour index, n, of 0.396. Both storage (G′) and loss modulus (G″) increased with an increase in frequency. Emulsions behaved like a liquid with G″ > G′ at lower frequencies; and like an elastic solid with G′ > G″ at higher frequencies. Effect of guar gum was more pronounced on dynamic properties. Phase angle values decreased from 89 to <10° with increasing frequency and indicated the viscoelasticity of WPI-stabilized emulsions with and without pectin/guar gum.     

Effect of whey protein enzymatic hydrolysis on the rheological properties of acid-induced gels

A protein dispersion blend of β-lactoglobulin and α-lactalbumin was heat-denatured at pH 7.5, hydrolyzed by α-chymotrypsin and then acidified with glucono-δ-lactone to form gels at room temperature. Heat treatment induced the formation of whey protein polymers with high concentration of reactive thiol groups (37 μmol/g). The reactive thiol group concentration was reduced by half after 40 min enzymatic hydrolysis. It was further reduced after enzyme thermal deactivation. During acidification, the first sign of aggregation for hydrolyzed polymers occurred earlier than for non hydrolyzed polymers. Increasing the hydrolysis duration up to 30 min resulted in more turbid gels characterized by an open microstructure. Elastic and viscous moduli were both reduced, while the relaxation coefficient and the stress decay rate constants were increased by increasing the hydrolysis duration. After one week storage at 5 °C, the hardness of gels made from hydrolyzed polymers increased by more than 50%. The effect of polymer hydrolysis on acid-induced gelation is discussed in relation to the availability and reactivity of thiol groups during gel formation and storage.     

Functional and technological aspects of whey powder and whey protein products

Commercial whey powder, whey protein concentrates and whey protein isolates (WPIs) were evaluated for certain functional properties and for their application in full‐fat and nonfat yoghurts. The functional properties of whey products varied, and the highest functionality was recorded in samples with high protein levels. Whey powder had the lowest foaming performance and emulsifying capacity, while WPIs possessed the best functional properties of all the other samples. Curd tension (CT), viscosity and syneresis were improved in yoghurts made using fortified cow's milk or reconstituted skim milk with any whey products, while whey powder had no impact on CT.     

The use of whey protein particles in gluten-free bread production,the effect of particle stability

Wheat dough has unique properties for bread making due to its elastic and strain hardening behaviour. A mesoscopically structured whey protein particle system possesses those elastic and strain hardening properties when mixed with starch to a certain extent. However, the extensibility is lower and the particles are more stable than gluten particles upon kneading, probably due to a too high degree of internal crosslinking. This study describes the relation between the number of disulphide bonds of a mesoscopic whey protein particle suspension blocked by NEM treatment and the resulting properties of a dough and bread prepared with that suspension. This study shows that the properties of the particle network are influenced by the ability to form disulphide bonds. Our study shows that a certain amount of disulphide bonds is essential, but too many disulphide bonds can lead to too stiff dough and poorer bread properties.     

Effect of whey and pea protein blends on the rheological and sensory properties of protein-based systems flavoured with cocoa

Whey and pea protein combined in different proportions (100W:0P, 75W:25P, 50W:50P, 25W:75P, 0W:100P) were used to prepare protein-based systems flavoured with cocoa and containing κ-carrageenan or κ-carrageenan/xanthan gum as thickeners. Steady and dynamic shear rheological properties of samples were measured at 10 °C and sensory differences were evaluated. Protein-based systems exhibited a shear-thinning flow behaviour that was fitted to the simplified Carreau model. Samples showed different viscoelastic properties, ranging from fluid-like to weak gel behaviour. For both types of system (with and without xanthan gum) viscosity, pseudoplasticity and elasticity rose on increasing the pea protein proportion in the blend. The sample with only whey protein obeyed the Cox-Merz rule, while in the rest of the samples complex viscosity was higher than apparent viscosity. Regarding sensory properties, the protein blend ratio mainly affected sample thickness, which rose as pea protein proportion increased. However, at the same time, the chocolate flavour and sweetness decreased and the off-flavour increased.     

Effect of dynamic heat treatment on the physical properties of whey protein foams

The influence of dynamically heat-induced aggregates on whey protein foams was investigated as a function of the thermal treatment applied with the aim of determining the optimal temperature for the production of heat-induced aggregates dedicated to foaming. The native protein solutions (2% w/v WPI; 50 mM NaCl) at neutral pH were heat-treated using a tubular heat exchanger between 70 °C and 100 °C. Protein denaturation and aggregation were followed by micro-differential scanning calorimetry, size exclusion chromatography, laser diffraction and dynamic light scattering. The protein solutions were whipped using a kitchen mixer to produce foams. Foam overrun, stability against drainage, texture and bubble size distribution were measured.     

Expanded functionality of modified whey protein dispersions after transglutaminase catalysis

The functionality of whey dispersions, prepared with a modified whey protein concentrate (mWPC) ingredient, was significantly altered after cross-linking with microbial transglutaminase (TGase) upon pH adjustment to 8. Test TGase-mWPC solutions, pH 8, gelled faster than control mWPC dispersions, as measured in real time; whereas, the gelling temperature of pretreated TGase-mWPC samples (37 °C, 2.5 h) increased from 67.8 to 74.8 °C with a minimal change in gel strength. Prolonged prior incubation with the enzyme (37 °C, 20 h) raised the gel strength in both control mWPC and TGase-mWPC dispersions, though these values were approximately 2.7 times lower in TGase-mWPC samples. Furthermore, the gelling temperature was raised by 9 °C after extensive polymerization. The water holding capacity was not impacted by enzymatic processing while emulsions prepared with TGase-mWPC dispersions proved very stable with no evidence of phase separation during storage at room temperature for 1 mo. Moreover, the apparent viscosity of TGase-mWPC emulsions exhibited a 10-fold increase compared to nonenzyme-treated mWPC samples. The particle size was nearly 11 μm in covalently linked TGase-mWPC test fractions compared with 8 μm in nonpolymerized mWPC dispersions. Ultimately, the functional characteristics of TGase-mWPC ingredients may be designed to deliver superior performance, especially with regard to improving heat and emulsion stability.     

Comparative effect of thermal treatment on the physicochemical properties of whey and egg white protein foams

The optimization of the functionalities of commercial protein ingredients still constitutes a key objective of the food industry. Our aim was therefore to compare the effect of thermal treatments applied in typical industrial conditions on the foaming properties of whey protein isolate (WPI) and egg white proteins (EWP): EWP was pasteurized in dry state from 1 to 5 days and from 60 °C to 80 °C, while WPI was heat-treated between 80 °C and 100 °C under dynamic conditions using a tubular heat exchanger. Typical protein concentrations of the food industry were also used, 2% (w/v) WPI and 10% (w/v) EWP at pH 7, which provided solutions of similar viscosity. Consequently, WPI exhibited a higher foamability than EWP. For WPI, heat treatment induced a slight decrease of overrun when temperature was above 90 °C, i.e. when aggregation reduced too considerably the amount of monomers that played the key role on foam formation; conversely, it increased foamability for EWP due to the lower aggregation degree resulting from dry heating compared to heat-treated WPI solutions. As expected, thermal treatments improved significantly the stability of WPI and EWP foams, but stability always passed through a maximum as a function of the intensity of heat treatment. In both cases, optimum conditions for foam stability that did not impair foamability corresponded to about 20% soluble protein aggregates. A key discrepancy was finally that the dry heat treatment of EWP provided softer foams, despite more rigid than the WPI-based foams, whereas dynamically heat-treated WPI gave firmer foams than native proteins.     

Effect of heat treatment and solution preparation procedure on colloidal stability of whey protein sour cherry beverage

In this study, a whey protein sour cherry beverage was prepared using whey protein concentrate, sour cherry concentrate, Angum gum, water and sugar as initial ingredients. Whey protein concentrate and gum solutions were prepared by four methods. Heat treatment of the solutions led to denaturation of proteins, a change in the solubility of proteins and sediment formation. Our results showed that denaturation of proteins made the peptide fragments of the proteins to bind the gum, thus preventing the separation of the serum.     

Effect of microbial transglutaminase treatment on thermal stability and pH-solubility of heat-shocked whey protein isolate

Whey protein isolate (WPI) dispersions (5% protein, pH 7.0) were subjected to heat-shock at 70 °C for 1, 5 and 10 min. The heat-shocked WPI dispersions were treated with microbial transglutaminase (MTGase) enzyme, and thermal properties and pH-solubility of the treated proteins were investigated. Heat-shocking of WPI for 10 min at 70 °C increased the thermal denaturation temperature (T_d) of β-lactoglobulin in WPI by about 1.5 °C. MTGase treatment (30 h, 37 °C) of the heat-shocked WPI significantly increased the T_d of β-lactoglobulin by about 6.3–7.3 °C when compared with heat-shocked only WPI at pH 7.0. The T_d increased by about 13–15 °C following pH adjustment to 2.5; however, the T_d of heat-shocked WPI was not substantially different from heat-shocked and MTGase-treated WPI at pH 2.5. Both the heat-shocked and the heat-shocked-MTGase-treated WPI exhibited U-shaped pH-solubility profiles with minimum solubility at pH 4.0–5.0. However, the extent of precipitation of MTGase-treated WPI samples at pH 4.0–5.0 was much greater than all heat-shocked and native WPI samples. The study revealed that while MTGase cross-linking significantly enhanced the thermal stability of β-lactoglobulin in heat-shocked WPI, it caused pronounced precipitation at pH 4.0–5.0 via decreasing the hydrophilic/hydrophobic ratio of the water-accessible protein surface.     

大豆多糖对乳清分离蛋白—乳状液稳定性与流变特性的影响

本文研究了大豆多糖（SSPS）与乳清分离蛋白（WPI）乳状液静电组装,形成乳状液聚集体,考察了不同浓度的SSPS对WPI-乳状液稳定性与流变特性的影响,以期提高体系的粘弹性,形成高流变特性的食品体系。将不同浓度的大豆多糖与2%乳清分离蛋白乳状液（油相为20%）静电组装,分析乳状液的粒径,Zeta-电位,稳定性指数,流变性质和微观结构。结合剪切流变与微流变技术,深入研究了SSPS对乳清分离蛋白（WPI）乳状液流体特性与结构的影响。结果表明:随着SSPS浓度的增加,WPI乳状液的粒径在添加0.25%SSPS时达到峰值（3350±0.35）nm,而后随着SSPS浓度的增加而降低;Zeta-电位绝对值呈递减的趋势,表明SSPS与WPI间产生静电吸附作用;SSPS静电吸附提高WPI乳状液的稳定性;剪切流变结果表明,SSPS浓度为0.5%时,其粘度最大,并在剪切速率为95.8 s-1处其粘度是WPI乳状液粘度的10倍以上;微流变结果表明,0.5%SSPS-WPI乳状液的MSD曲线出现平台区,表明其弹性指数（EI）与宏观粘度指数（MVI）均显著提高达到最大值。微观结构结果表明,0.5%SSPS-WPI乳状液形成均一的乳状液聚集体。本研究将有助于理解大豆多糖与蛋白质乳状液的相互作用,同时为低脂高流变特性的食品（如蛋黄酱、调味汁、巧克力和植脂奶油等）生产提供理论指导。      

Improved emulsion stabilizing properties of whey protein isolate by conjugation with pectins

Functional properties of glyco-protein conjugates of the anionic polysaccharide pectin with whey protein isolate, obtained by dry heat treatment at 60 °C for 14 days, have been investigated in O/W emulsions containing 20% (w/w) soybean oil and 0.4% (w/w) protein both at pH 4.0 and 5.5. Emulsion stabilizing properties of mixtures and conjugates were compared at five protein to pectin weight ratios by determining changes in droplet size distribution and extent of serum separation with time. The results indicated that the dry heat-induced covalent binding of low methoxyl pectin to whey protein, as shown by SDS-PAGE, led to a substantial improvement in the emulsifying behaviour at pH 5.5, which is near the isoelectric pH of the main protein β-lactoglobulin. At pH 4.0, however, a deterioration of the emulsifying properties of whey protein was observed using either mixtures of protein and pectin or conjugates.The observed effects could be explained by protein solubility and electrophoretic mobility measurements. The protein solubility at pH 5.5 was hardly changed using mixtures of protein and low methoxyl pectin or conjugates, whereas at pH 4.0 it was decreased considerably. Electrophoretic mobility measurements at pH 5.5 revealed a much more pronounced negative charge on the emulsion droplets in the case of protein–pectin conjugates, which clearly indicated that conjugated pectin did adsorb at the interface even at pH conditions above the protein's iso-electric point. Hence, the improved emulsifying properties of whey protein isolate at pH 5.5 upon conjugation with low methoxyl pectin may be explained by enhanced electrosteric stabilization.Comparing two different commercial pectin samples, it was clearly shown that the dextrose content during dry heat treatment of protein–pectin mixtures should be as low as possible since protein–sugar conjugates not only resulted in increased brown colour development, but also gave raise to a largely decreased protein solubility which very badly affected the emulsifying properties.     

Rheological characterization and electrokinetic phenomena of charged whey protein dispersions of defined sizes

A multi-step processing technique produced large colloidal particles from whey proteins, prompting instantaneous thickening upon hydration. Analysis of the rheological characteristics and zeta potential of the modified whey suspensions of defined particle sizes allowed investigation into the role of size on ingredient functionality. Preliminarily, the modified protein powders were sieved to achieve three size ranges, and analyzes were conducted on each of the three distributions and the non-sieved fractions. Following hydration, steady and oscillatory shear analyzes were performed using a controlled stress rheometer to determine rheological characteristics. Intrinsic viscosity was determined with a capillary viscometer and application of the Huggins equation. Zeta potential was calculated from colloidal electrophoretic mobility, measured with a ZetaPALS analyser. After thorough hydration, particle-size analysis revealed a size increase of >1.3 times for each fraction. When analysed on a protein basis, increasing particle size yielded an increase to intrinsic viscosity, flow behavior index, zero shear viscosity, and a decreased zeta potential and consistency coefficient. Knowledge of the interrelationship between zeta potential, rheological properties, and particle size of the modified whey ingredient will further advance an understanding of the functionality of this protein ingredient.