Gel Properties of Whey Protein Concentrates as Influenced by Ionized Calcium

Ionic calcium in four whey protein concentrates (WPC) was decreased using sodium tripolyphosphate (NaTPP) or ethylenediamine tetraacetic acid (EDTA) and effects on gel properties were determined. Total calcium ranged from 0.22–0.41 g/100g WPC and ionic calcium 2.98–47.25 mg/100g protein. Hardness was maximized and expressible moisture (EM) minimized in three WPC gels with 10 mM NaTPP. EDTA had a similar effect on one WPC gel. Addition of 10 mM NaTPP decreased ionic calcium to 5.23–10.31 mg/100g protein. NaTPP or CaCl₂ did not improve hardness or EM of one WPC gel which contained the lowest total and ionized calcium. Chelating agents were effective in improving gel properties of WPC containing higher than optimal calcium.     

Factors Influencing Whey Protein Gel Rheology: Dialysis and Calcium Chelation

Influence of dialyzable compounds on the Theological properties (shear stress and shear strain at failure) of heat-induced whey protein concentrate (WPC) and whey protein isolate (WPI) gels was examined. Dialyzing WPC and WPI suspensions prior to gelation increased the stress of two of three WPC gels and a WPI gel. Dialysis also significantly increased the strain of the same two WPC gels, normalizing all strain values. Replacement of calcium lost through dialysis did not significantly change gel rheology. However, chelating calcium caused a significant decrease in the stress of all gels: a minimum amount of calcium and/or a calcium complex appears to have a major role in whey protein gelation.     

Viscoelastic properties of caseinmacropeptide isolated from cow,ewe and goat cheese whey

Caseinmacropeptide (CMP) is a C‐terminal glycopeptide released from κ‐casein by the action of chymosin during cheese‐making. It is recognised as a bioactive peptide and is thought to be an ingredient with a potential use in functional foods. CMP occurs in sweet cheese whey and whey protein concentrate (WPC). Its composition is variable and depends on the particular whey source and the fractionation technology employed in the isolation. There were no significant (P < 0.05) differences in the relative apparent viscosities between species of CMPs (cow, ewe and goat). Analyses at different pH (2, 4, 7, 10), ionic strength (0, 0.2, 0.4 and 0.7 as NaCl molarity) and protein concentration (50, 100 and 200 g kg^?1) at temperatures from 10 to 90 °C carried out found pH 7 and high protein concentration (200 g kg^?1) conditions to be the best for CMP solutions to keep low and constant relative viscosity values with increasing temperature up to 75 °C. The viscoelastic properties–storage modulus, loss modulus and phase angle–of the different CMPs and WPC solutions were determined. Heat‐induced rheological changes in CMP solutions occurred at moderate temperatures (40–50 °C) with no appreciable differences in viscosity. Gelation took place significantly (P < 0.05) earlier in goat CMP (41 °C), followed by cow CMP (44 °C), ewe CMP (47 °C) and WPC (56 °C). Heating at 90 °C showed that WPC required significantly (P < 0.05) longer times to form gels (>5 min) than the CMPs (<5 min). WPC gels had higher (>20°) phase angle than CMP (<20°), which could be associated with untidy structures, limiting elastic properties of the gel. Copyright © 2006 Society of Chemical Industry     

Properties of gels from whey protein concentrate and honey at different pHs

Structural and functional properties of heat-induced gels from whey protein concentrate (WPC)-honey prepared at pHs 3.75, 4.2 and 7.0 were analyzed. Gel structure was observed by scanning electron microscopy, and the apparent transition temperature for protein denaturation was determined by differential scanning calorimetry. The solubility of the protein components in different extraction media, and the water-holding capacity, firmness, elasticity, relaxation time, adhesivity, cohesiveness and color of gels were determined. Results show that disulfide interchange reactions are important in determining the elasticity, water-holding capacity, relaxation time and cohesiveness of WPC gels. Honey decreases the relaxation time of gels prepared at pHs 7.0 and 4.2, and increases the browning and the water-holding capacity of gels, the apparent transition temperature of WPC dispersions at the three pHs assayed, and the adhesivity of acidic gels. The solubility of the protein constituents of gels in a pH 8.0 buffer increases slightly at honey concentrations of 27.5% or more, which correlates with a decrease in the gel cohesiveness, having these gels a structure with smaller pores. The products obtained could be utilized in the formulation of different desserts, such as flans and cake and tart fillings.     

Whey protein concentrate gels with honey and wheat flour

Structural and functional properties of whey protein concentrate (WPC) gels with different honey and wheat flour contents, prepared at pHs 3.75, 4.2 and 7.0, were analysed. Gel structure was observed by scanning electron microscopy. The apparent transition temperatures for protein denaturation and starch gelatinization were determined by differential scanning calorimetry. Gels were characterised through solubility assays in different extraction solutions and polyacrylamide gel electrophoresis of the soluble protein components. The firmness, elasticity, relaxation time, adhesivity and cohesiveness of gels were determined, and the water-holding capacity and superficial colour of gels were also studied. Results suggest that wheat flour could interact with whey proteins, and produces a decrease in the protein solubility of WPC gels, and in the temperature of whey protein denaturation. The effect of wheat flour on the functional properties of WPC gels was different at acidic than at neutral pH: the presence of wheat flour produced an increase in the relaxation time and in the cohesiveness of gels prepared at pH 3.75, whereas at neutral pH a decrease in both properties was observed. Honey and flour content increased the water-holding capacity and browning of WPC gels.     

乳清蛋白质浓缩物的流变学性质

本研究以3种工业化生产的乳清蛋白浓缩物(WPC)的再制溶液为对象,测定其不同条件下的流动特性,即在剪切速率3～1321/sec、温度5～65℃、总固形物浓度5～40％,pH3～10等条件下,溶液的剪切应力与剪切速率和剪切应力与剪切时间的关系。WPC溶液的流变学行为与溶液的浓度、温度、pH有关。在多数实验条件下,WPC溶液具有假塑性液体性质,可以用幂律模式(power law module)来表示,在极端条件下,溶液的流动特性则接近牛顿液体或塑性液体。     

Characterisation of heat-set milk protein gels

Milk protein solutions [10% protein, 40/60 whey protein/casein ratio containing whey protein concentrate (WPC) and low-heat or high-heat milk protein concentrate (MPC)] containing fat (4% or 14%) and 70–80% water, form gels with interesting textural and functional properties if heated at high temperatures (90 °C, 15 min; 110 °C, 20 min) without stirring. Adjustment of pH before heating (HCl or glucono-δ-lactone) produces soft, spoonable gels at pH 6.25–6.6, but very firm, cuttable gels at pH 5.25–6.0. Gels made with low-heat MPC, WPC and low fat gave some syneresis; high-fat gels were slightly firmer than low-fat gels. Citrate markedly reduced gel firmness; adding calcium had little effect on firmness, but increased syneresis of low-heat MPC/WPC gels. The gels showed resistance to melting, and could be boiled or fried without flowing. Microstructural analysis indicated a network structure of casein micelles and fat globules interlinked by denatured whey proteins.     

The effect of shear on the rheology and structure of heat‐induced whey protein gels

The influence of mechanical shearing on the small deformation properties and microstructure of heat‐induced whey protein gel has been studied. The viscoelastic properties of these gels at different concentrations of 10% and 20% (w/w) exposed to different shear rates of 0, 50, 100, 200 and 500 s^?1 during gelation were measured using dynamic oscillatory rheometry. The structure of both the shear treated and unsheared gels was then investigated using light microscopy. The results showed that the storage modulus of the gels at both concentrations was increased by increasing the shear rate exposure during gelation while the shear‐treated gels were more elastic and showed frequency‐independent behaviour. As the total protein concentration of the gel increased, the viscoelastic properties of the gels also increased significantly and the gels showed greater elasticity. The gels obtained from the higher shear rate exposure were stronger with higher elastic moduli at both protein concentrations. Images of the gels obtained using light microscopy showed that shearing resulted in phase separation and some aggregation in the structure of the gels at both concentrations. However, the shearing rates applied in this study were not enough to cause aggregation breakdown in the gel network.     

Polymer and Ion Concentration Effects on Gellan Gel Strength and Strain

Failure stresses and strains were measured in compressive, tensile and torsional modes on gellan gels at four polymer (0.6–1.8% w/v) and seven Ca⁺⁺ (1.5–60 mM) concentrations. Shear stresses at failure were equal in all three testing modes and proportional to gellan content. Low calcium gels increased linearly in strength with Ca⁺⁺ concentration until it reached a level of about 0.5 calcium ions per repeat tetrasaccharide unit of gellan gum polymer. Gel strength decreased linearly with Ca⁺⁺ at higher concentrations. Low calcium gels were extensible with failure strains decreasing as the logarithm of Ca⁺⁺; whereas high calcium gels were brittle and failed at a constant strain, the value of which was twice as high in compression and torsion as in tension.     

Whey protein concentrate: Autolysis inhibition and effects on the gel properties of surimi prepared from tropical fish

Effects of whey protein concentrate (WPC) on autolysis inhibition and gel properties of surimi produced from bigeye snapper (Priacanthus tayenus), goatfish (Mulloidichthys vanicolensis), threadfin bream (Nemipterus bleekeri) and lizardfish (Saurida tumbil) were investigated. WPC (0–3%) showed inhibitory activity against autolysis in all surimi at both 60 and 65 °C in a concentration-dependent manner. Myosin heavy chain (MHC) of surimi was more retained in the presence of WPC. Breaking force and deformation of kamaboko gels of all surimi increased as added levels of WPC increased (P < 0.05). This was associated with lower levels of protein degradation, as evidenced by the decrease in trichloroacetic acid-soluble peptide content (P < 0.05). WPC at 3% (w/w) significantly decreased the whiteness of gels. However, water-holding capacity of kamaboko gels was improved with increasing concentration of WPC. The microstructure of surimi gels generally became denser with the addition of WPC.     

Appearance and Textural Properties of Sheared Low Concentration Potato Protein Gels—Impact of Drying Method,pH, and Ionic Strength

The objective was to prepare sheared gels of potato protein concentrate and evaluate the effect of pH (3, ～4, ～7), ionic strength (15 or 200 mM) and protein drying conditions (spray or freeze drying) on the final appearance and rheological characteristics. Heat‐set gels 3 % (w/w) at a high ionic strength (200 mM) resulted in an inhomogeneous appearance with presence of clots, while low ionic strength (15 mM) gave homogenous structures. Gels prepared at pH 3 became transparent while preparation above pH 3.0 resulted in high turbidity. Heat treatment and cooling resulted in gelation for all samples except freeze dried powder at pH 3.0. Flow curves during shear from 0.1 to 100 s^?1 were fitted by the Herschel–Bulkley model indicating shear thinning behavior for all samples except the freeze dried sample at pH 3 which displayed a Newtonian behavior. Oscillatory measurements after shear indicated viscus behavior (phase angle above 45°) for the spray dried sample at pH 3, and gelled behavior (phase angle above 45°) for the remaining gelled samples. Structure recovery was observed after shear in all samples except at pH 3.0. The data shows potato protein can be used as ingredient in protein beverages.     

Moisture migration in idealized bilayer systems: relationships among water-associated properties, structure, and texture

The effects of composition and thermal treatment on the water sorption and diffusional properties of idealized protein gels arranged in bilayer configurations were determined; these water binding/migration properties were related to the mechanical characteristics of the gels. Samples were prepared from whey protein concentrate (WPC), they consisted of water:WPC ratios of 1.5 to 5.67, and were thermally set for 20–60 min. Moisture migration rates from samples interfaced with filters were determined, as were moisture sorption capacities of samples immersed in water. The physical properties of the gels were assessed by uniaxial compression and microscopy. Results showed that gel strength and consequent extent of protein interaction—as affected by thermal treatment—controlled the ability of the gel structure to absorb water. Sorption was exponentially correlated with gel modulus and linearly correlated with a function of protein content, heating time, and immersion time. Rates of diffusion from interfaced gels were dependent solely on water content. It was concluded that the degree of protein interaction, whether influenced by concentration or thermal treatment, affected network extensibility and thus the capacity of the gels to act as receptors of moisture. Results have implications for the functionality of shelf-stable sandwiches and other multicomponent foods.     

Gelation of mixed systems whey protein concentrate–gluten in acidic conditions

Gels of whey protein concentrate (WPC)–gluten were prepared by heating WPC–gluten dispersions (10% whey protein/0–5–10% gluten protein, w/w; pH 3.75 or 4.2). Gels were characterized through solubility assays in different extraction solutions, measures of water-holding capacity (WHC), firmness, elasticity and relaxation time, and light microscopy. Differential scanning calorimetry (DSC) of WPC–gluten dispersions was also performed. Gluten increases the firmness and elasticity of gels, mainly at pH 4.2. The WHC also increases with gluten content, being higher at pH 3.75 than at pH 4.2. Solubility assays indicate that electrostatic forces, hydrophobic and H bindings would be involved in maintaining the gel structure of WPC gels at pH 3.75 and 4.2, whereas in mixed gels of WPC–gluten, the principal forces responsible for the maintenance of the gel structure at these pHs would be hydrophobic and H bindings, and in gels prepared at pH 4.2 also disulfide bonds, but in a minor extent. The presence of gluten shifts the apparent transition temperature for whey protein denaturation towards lower temperatures. Gels with gluten present a smooth network with gaps and a more elastic appearance, as observed by light microscopy.     

淀粉-乳清蛋白复合条件对体系润滑特性的影响

探索浓缩乳清蛋白（whey protein concentrate,WPC）是否参与淀粉糊化过程及复合质量分数对淀粉-WPC复合体系润滑特性的影响,选取聚二甲基硅氧烷作为摩擦副,模拟口腔加工条件对淀粉-WPC复合体系的润滑特性进行研究。结果显示：在口腔加工的0～60 s时间范围,WPC参与和未参与淀粉糊化,2种复合方式得到复合体系的润滑性能存在显著差异（P<0.05）,且在不同植物源淀粉间存在显著差异（P<0.05）;在WPC复合质量分数1%～7%范围内,WPC的复合显著提升了原淀粉凝胶体系的润滑特性,且WPC质量分数对复合体系润滑特性提升呈非线性关系具有正显著影响（P<0.05）。该研究为提升淀粉蛋白质基质食品的质地口感提供理论参考。     

Viscous properties of microparticulated dairy proteins and sucrose

Slurries of whey protein concentrate (WPC) or sodium caseinate (Na-CN) mixed with sucrose (36% T.S.) were subjected to microparticulation by a high shear homogenizer operated at 27,000 rpm for 2, 4, and 6 min to facilitate gel formation. After microparticulation treatment, the milk protein and sucrose slurries were evaporated at 85 degrees C for 60 min under a partial vacuum (20 to 45 mm of Hg) to form composite gels. Particle sizes and viscoelastic properties were determined before microparticulation treatment. Microparticulation reduced the particle size of WPC-sucrose slurries from an average size of 330 to 188 nm after 4 min and NaCN-sucrose slurries from 270 to 35 nm after 2 min. The WPC-sucrose composites were gel-like, but NaCN-sucrose composites did not gel. Viscoelastic properties of heated WPC-sucrose composites were liquid-like, exhibiting significant reduction in storage modulus and complex viscosity. Microparticulation reduced particle sizes, which resulted in softer gels as time of shearing increased.     

Effect of Hardness of Plastic Fat on Structure and Material Properties of Fish Protein Gels

Textural modification of fish protein gels by incorporation of plastic fat was investigated by examining the effect of the physical properties of fat on the structure and the material properties of protein gels. Material properties of fat-containing protein gels were influenced largely by fat distribution pattern which was, in turn, affected by fat hardness. Both compressive and shear forces reached their maximum when fat of 1.8 cm^–1 hardness index (HI) was added at a level of 15% (fat/muscle). Addition of medium hard fat (0.54–0.78 cm^–1 HI): (1) prevented a sponge-like texture development by improving freeze-thaw stability; (2) increased plastic deformation, thus making cooked gels less rubbery; (3) overcame the weakening of texture caused by cooking at the critical zone (60–70°C); and, (4) minimized the variations in textural strength resulting from cooking.     

Foaming and Emulsifying Properties of Whey Protein Concentrates As Affected by Lipid Composition

Freeze-dried WPC, containing 35 and 75% protein were manufactured by pretreating whey with calcium chloride and heat. These and commercial WPC were subjected to proximate analysis and lipid classes, phospholipid classes, free fatty acids (FFA), and monoacylglycerols (MAG) composition were determined. Solubility, thermal, foaming, and emulsifying properties of the WPC were studied. Pretreatment increased calcium and phosphorus contents and decreased the contents of all other minerals. The pretreatment had no effect on solubility, denaturation enthalpy, and onset temperature of denaturation of WPC. These values were comparable to those of commercial WPC. Foaming capacity and emulsion stability were unaffected, but foam stability increased and emulsifying capacity decreased due to pretreatment. Overall, total lipids and lipid class contents of experimental WPC were too low to affect surface properties of WPC.     

热诱导温度与pH值对乳清浓缩蛋白凝胶结构和性质的影响

以乳清浓缩蛋白（whey protein concentrate,WPC）为原料,采用动态流变仪、光学微流变仪、圆二色谱仪、荧光分光光度计及扫描电镜探究WPC凝胶形成过程、分子间相互作用和微观结构,并研究热诱导温度（60、85 ℃）和pH值（2.0、4.5、7.0、9.0）对WPC凝胶性质和结构的影响机理。结果表明：pH值通过改变电荷密度影响WPC的凝胶结构;热诱导温度为85 ℃时,蛋白质分子展开更充分,α-螺旋结构含量较低,内源荧光的最大荧光强度波长处红移明显,形成的WPC凝胶具有更高的弹性模量和黏性模量;凝胶的弹性因子和宏观黏度指数较高,固液平衡值较低;相互作用力分析结果说明较高的热诱导温度能促进疏水相互作用、氢键与二硫键的形成,从而改善WPC凝胶的性质和结构。     

Whey Protein-Based Gel as a Model Material for Studying Initial Cleaning Mechanisms of Milk Fouling

The dissolution kinetics and mechanical properties of whey protein concentrate (WPC) gels were investigated as part of a general study on cleaning mechanisms of milk fouling. The dissolution results showed that the WPC gel is a suitable model material to simulate milk fouling and the dissolution process is a major factor controlling the cleaning process. The hardness, elastic modulus, and fracture load of the WPC gels decreased significantly when they were treated with alkaline solution, indicating that certain physical and chemical changes occurred in these treated gels; as a result, different dissolution rates were observed. The results obtained in this article provide a good foundation for further studies on the cleaning mechanisms of milk fouling using WPC gels.     

Thermal gelation of commercial whey protein concentrate: influence of pH 4.6 insoluble protein on thermal gelation

Thermal gels were prepared from solutions of seven commercial whey protein concentrates (WPCs) and were found to vary considerably in strength, as determined by a compressive rheological measurement method. Further studies were carried out on one WPC (WPC5) which had far superior gelling properties to the other six WPCs and revealed that this WPC had a substantial level of protein that was insoluble (sedimentable) at pH 4.6 on centrifugation at 10000 g for 30 min but not insoluble under similar conditions at pH 7.0. When this pH 4.6 insoluble material was removed the gelling properties of WPC5 decreased considerably. Alkaline treatment (pH 9.0 for 3 hours) of a WPC5 supernatant devoid of pH 4.6 insoluble material resulted in a substantial improvement in gelling properties and generation of further pH 4.6 insoluble material. Gel electrophoresis studies and differential scanning calorimetry confirmed that the pH 4.6 insoluble material recovered from WPC5 and the alkaline treated WPC5 supernatant contained denatured protein which was associated via covalent and non-covalent interactions. Transmission electron microscopy of thermal gels prepared from WPC5 solutions containing and devoid of pH 4.6 insoluble material indicated that gel micro structure was dependent on the presence or absence of this denatured aggregated protein material in dispersion prior to heat treatment. Overall, the results suggested that the pH 4.6 insoluble, but pH 7.0 soluble, protein present in a WPC5 dispersion influenced gel microstructure on heating in a manner that had a positive influence on gel rheology.