PARTIAL CHARACTERIZATION OF A WHEY PROTEIN CONCENTRATE AND ITS ENZYME HYDROLYSATES

A whey protein concentrate (WPC) was produced from fresh whey by ultrafiltration (MW cut off 10 kDa) and lyophilization. Enzymatic hydrolysis was performed with three enzyme systems: pancreatin (PA), protamex (PR) or alcalase 0.6L (AL) to produce hydrolysates with 20% degree of hydrolysis (DH). The peptide profiles of the hydroly sates were determined by high performance capillary electrophoresis (HPCE). The relationship between enzyme system and preferential protein substrate could be established. The alcalase hydrolysate (ALH) differed from the other two hydrolysates, and the enzyme showed the lowest specificity for β‐lactaglobulin. Considering the protein content from WPC the pancreatin hydrolytic system was the most efficient leaving only 4.69% unhydrolyzed protein in the final hydrolysate (PAH). For 20% degree of hydrolysis alcalase left 7.98% unhydrolyzed protein, while protamex left 9.81% unhydrolyzed protein in the final hydrolysate.     

APPLICATION OF SURFACE FRICTION MEASUREMENTS FOR SURFACE CHARACTERIZATION OF HEAT-SET WHEY PROTEIN GELS

The surface properties of heat‐set whey protein gels (14 wt %) was studied by measuring the friction at the gel's surface. A simple device was constructed that can be conveniently attached to a Texture Analyzer. Surface friction forces of gels with and without addition of salt were measured as a function of sliding speed and surface load. Surface friction strongly depended on the sliding speed for all three gel systems over the speed range 0.01 mm/s to 10 mm/s. The gel without salt addition showed the highest speed dependency, while the gel containing 200 mM NaCl had the lowest speed dependency. Surface load tests showed nearly linear relationships for both protein gels (with and without salt addition). Unlike solid materials, both protein gels exhibited a surface friction even as the surface load approached zero. Possible contributions of surface attraction and viscous flow to the measured forces are discussed. Results from surface friction tests were further confirmed by optical observation of the surface using a confocal laser scanning microscope (CLSM), where a very smooth surface was observed for the whey protein gel without salt addition, but a much rougher surface was observed for the gel containing 200 mM NaCl.     

OPTIMIZING STABILITY OF ORANGE JUICE FORTIFIED WITH WHEY PROTEIN AT LOW pH VALUES

Abstract The influence of temperature, heating time and pH on the stability of whey protein-fortified Valencia orange juice was determined by uronic acid content, degree of esterification (DE), % transmission measurements (%T) and capillary electrophoretic analysis of the juice-protein supernatants. Uronic acid content and charge of pectins showed no significant change in heat-treated samples with added proteins. The %T decreased with decreasing pH and increasing temperature and heating time for α-lactalbumin (α-lac), β-lactoglobulin (β-lg) and whey protein isolate (WPI). The lowest transmission values were shown at pH 3.0 and 85C. Capillary electropherograms confirmed more extensive juice-protein interactions in WPI and β-lg added juices than in those containing α-lac, especially at low pH, resulting in more stable juice-protein mixtures.     

COLD GELATION OF WHEY PROTEIN EMULSIONS

Stable and homogeneous emulsion‐filled gels were prepared by cold gelation of whey protein isolate (WPI) emulsions. A suspension of heat‐denatured WPI (soluble WPI aggregates) was mixed with a 40% (w/w) oil‐in‐water emulsion to obtain gels with varying concentrations of WPI aggregates and oil. For emulsions stabilized with native WPI, creaming was observed upon mixing of the emulsion with a suspension of WPI aggregates, likely as a result of depletion flocculation induced by the differences in size between the droplets and aggregates. For emulsions stabilized with soluble WPI aggregates, the obtained filled suspension was stable against creaming, and homogeneous emulsion‐filled gels with varying protein and oil concentrations were obtained. Large deformation properties of the emulsion‐filled cold‐set WPI gels were determined by uniaxial compression. With increasing oil concentration, the fracture stress increases slightly, whereas the fracture strain decreases slightly. Small deformation properties were determined by oscillatory rheology. The storage modulus after 16 h of acidification was taken as a measure of the gel stiffness. Experimental results were in good agreement with predictions according to van der Poel's theory for the effect of oil concentration on the stiffness of filled gels. Especially, the influence of the modulus of the matrix on the effect of the oil droplets was in good agreement with van der Poel's theory.     

GEL CHARACTERISTICS OF β-LACTOGLOBULIN, WHEY PROTEIN CONCENTRATE AND WHEY PROTEIN ISOLATE

The gelation characteristics of β-lactoglobulin, whey protein isolate and whey protein concentrate at varying levels of protein (6–11%), sodium chloride (25–400 mM), calcium chloride (10–40 mM) and pH (4.0–8.0) were studied in a multifactorial design. Small scale deformation of the gels was measured by dynamic rheology to give the gel point (°C), complex consistency index (k*), complex power law factor (n*) and critical strain (γ_c). The gel point decreased and turbidity increased with increasing calcium level. The denaturation temperature measured by differential scanning calorimetry was measured at higher pH values. Large scale deformation at 20% and 70% compression was measured using an Instron Universal Testing machine. The true protein level had the largest effect on the stress required to produce 20% and 70% compression and on the consistency (k*) of the gels.     

PROCESSING OF WHEY BY MEANS OF MEMBRANES AND SOME APPLICATIONS OF WHEY PROTEIN CONCENTRATE

Data are given for processing Gouda cheese whey by reverse osmosis as preconcentration before transport or evaporation or ultrafiltration. Concentration costs for reverse osmosis are less than those for evaporation at ×2 concentration. Data are given for processing Gouda whey by ultrafiltration. Means to reduce oxidation defects in dried whey protein concentrate during storage are discussed. Applications of whey protein concentrate in soft drinks and in flour confectionery are described.     

RHEOLOGICAL PROPERTIES OF WHEY PROTEIN CONCENTRATE GELS

The rheological properties of heat whey protein concentrate gels were studied by dynamic oscillation rheometry. A whey protein concentrate of 75% protein was used to make solutions of 10.3, 12.5 and 14.5% protein (w/w), which were heated to 90C for gel formation. Specific attention was focused on the temperature dependence of the mechanical properties of the gels during cooling and reheating. In all cases the magnitude of the complex modulus |G*| was found to increase with decreasing temperatures from 90 to 30C. The tan δ, which is related to the relative viscoelasticity of the gels, increased with decreasing temperatures from 90 to 60C. At temperatures between 60 and 30° C, tan δ remained constant. The dependence of |G*| and tan δ on temperature was found to remain constant during heating and cooling between 30 and 70C, indicating that rheological changes were reversible within this temperature range.     

乳清蛋白肽脱苦工艺的研究

对乳清蛋白肽脱苦的工艺条件进行研究.通过单因素实验和正交实验优化,综合考虑脱苦效果和蛋白质吸附率等指标,确定选用本吸附剂脱苦工艺条件为:乳清蛋白肽浓度20%,吸附剂(配比为壳聚糖:环糊精1:4),用量15%,吸附温度80℃,吸附时间5 min-10 min,此时乳清肽的苦味基本去除.     

VISCOELASTIC PROPERTIES OF WHEY PROTEIN CONCENTRATE GELS WITH HONEY AND WHEAT FLOUR AT DIFFERENT pH

Viscoelasticity of heat-induced gels from whey protein concentrate, with different contents of honey and wheat flour, and prepared at pH 3.75, 4.2 and 7.0, was studied by using dynamic rheological assays. The elastic modulus of gels prepared at neutral pH was higher than the corresponding to acidic gels, probably due to the fact that sulphydryl-disulfide interchange reactions are favored at neutral pH. Honey decreased the elastic modulus and increased the viscous modulus and the complex viscosity in all conditions assayed. Wheat flour increased the elastic modulus, and all samples exhibited a gel-type behavior except at high honey content.

PRACTICAL APPLICATIONS

Honey and wheat flour modifies the properties of whey protein concentrate gels. Both components have opposite effects: honey increases the viscous-like behavior and wheat flour the solid-like behavior of gels in all conditions assayed. The different characteristics of gels prepared at different pHs and with different amounts of honey and wheat flour could be used in different formulated foods, as desserts.     

乳清蛋白凝胶条件的研究

以乳清蛋白为研究对象，研究了乳清蛋白浓度、温度、加热时间、pH值、金属离子等因素对乳清蛋白凝胶形成的作用。结果显示，乳清蛋白形成凝胶的基本条件是乳清水溶液浓度大于0．133g／mL，温度高于85℃±2℃，当温度在85℃±2℃～90℃±2℃之间，凝胶形成时间随乳清蛋白浓度变大而减少，在沸水中乳清蛋白浓度对凝胶形成时间影响不大，在19min左右；酸性条件下乳清蛋白形成凝胶的最适pH为5．3，pH小于1．2在沸水中加热30min，乳清蛋白形成碎块状凝胶，碱性条件下形成凝胶的最适pH为8．3，pH大于12．8在沸水中加热30min，乳清蛋白变为红色；钙离子的添加可使乳清蛋白形成凝胶所需时间减少到6min。