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.     

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.     

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.     

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.     

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.     

CHARACTERIZATION OF TEXTURED WHEY PROTEIN PRODUCED AT VARYING PROTEIN CONCENTRATIONS

This research investigated the range of whey protein in a whey protein/starch mixture needed to produce an extrusion-textured whey product that contained a fibrous texture. It was determined that protein levels ranging from 48 to 64% were necessary for fiber formation. The functionality of textured whey protein (TWP) extrudates produced at three protein levels (48, 53 and 64%) from three different whey sources was characterized at three pH values (3, 5 and 7) and four temperatures (25, 50, 70 and 90C) with respect to solids lost (SL) and water-holding capacity (WHC). Significant differences were found in SL and WHC for each of the four variables. The consumer acceptability of beef patties extended by 50% TWP containing 48% protein was more acceptable to consumers than patties containing 50% textured vegetable protein, but scored lower than the 100% beef patties.

PRACTICAL APPLICATIONS

This study determined the maximum and minimum amount of whey protein in a whey protein/starch mixture required to produce an extrusion-textured whey product that contained a fibrous texture for use as a meat extender. There were no functional benefits of increasing the concentration of whey protein from 48%, which would not likely be practiced because whey protein is more costly than starch. Beef patties extended with 50% textured whey protein showed less cook loss, fat loss and diameter reduction than 100% beef patties while having sensory scores that were higher than patties extended with 50% textured vegetable protein.     

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。     

VISCOELASTIC PROPERTIES OF HEAT-SET WHEY PROTEIN EMULSION GELS

The viscoelastic properties of heat-set whey protein gels and whey protein-stabilized emulsion gels have been studied using the dynamic oscillatory rheometry technique. The storage modulus was monitored and analysed for pure protein gels and emulsion gels over a wide range of protein concentrations. The dependence of storage modulus on protein concentration is different for gels of low and high modulus. At low protein concentrations, the increase of storage modulus is much more sensitive to the increase of protein concentration. The protein-coated oil droplets behave as active filler particles and dramatically enhance the gel strength. The effect of the oil volume fraction on the rheology has been investigated for emulsion gels containing 11 vol. %, 20 vol. % and 45 vol. % Trisun oil. The formula of van der Poel fails to describe the experimental results. This is attributed to the strongly flocculated state of the emulsion system.     

FUNCTIONAL PROPERTIES OF HIGH HYDROSTATIC PRESSURE-TREATED WHEY PROTEIN

Surface hydrophobicity, solubility, gelation and emulsifying properties of high hydrostatic pressure (HHP)‐treated whey protein were evaluated. HHP treatment of whey protein buffer or salt solutions were performed at 690 MPa and initial ambient temperature for 5, 10, 20 or 30 min. Untreated whey protein was used as a control. The surface hydrophobicity of whey protein in 0.1 M phosphate buffers treated at pH 7.0 increased with an increase in HHP treatment time from 10 to 30 min. HHP treatments of whey protein in salt solutions at pH 7.0 for 5, 10, 20 or 30 min decreased the solubility of whey proteins. A significant correlation was observed between the surface hydrophobicity and solubility of untreated and HHP‐treated whey protein with r = ?0.946. Hardness of HHP‐induced 20, 25 or 30% whey protein gels increased with an increase in HHP treatment time from 5 to 30 min. An increase in the hardness of whey protein gels was observed as whey protein concentration increased. Whey proteins treated in phosphate buffer at pH 5.8 and 690 MPa for 5 min exhibited increased emulsifying activity. Whey proteins treated in phosphate buffer at pH 7.0 and 690 MPa for 10, 20 or 30 min exhibited decreased emulsifying activity. HHP‐treated whey proteins in phosphate buffer at pH 5.8 or 7.0 contributed to an increase in emulsion stability of model oil‐in‐water emulsions. This study demonstrates that HHP treatment of whey protein in phosphate buffer or salt solutions leads to whey protein unfolding observed as increased surface hydrophobicity. Whey proteins treated in phosphate buffers at pH 5.8 and 690 MPa for 5 min may potentially be used to enhance emulsion stability in foods such as salad dressings, sausage and processed cheese.