DRYING RATE EFFECT ON THE PROPERTIES OF WHEY PROTEIN FILMS

The effects of drying temperature, drying relative humidity and film thickness on the drying characteristics, water vapor permeability, and tensile properties of glycerol (Gly)-plasticized whey protein isolate (WPI) films were investigated. 50%WPI:50%Gly and 60%WPI:40%Gly (dry basis) films were studied. Constant rate periods were compared among films. A higher temperature (95C) and lower relative humidity (30%RH) increased the slope of the weight versus time plot during the constant rate period, indicating shorter drying times to reach the falling rate period. Water vapor permeabilities were significantly lower for films dried at 95C and 30%RH than for films dried at 21C and 50%RH. Films dried at 95C and 30%RH were generally thinner, stiffer, stronger, and less extendable than films dried at 21C and 50%RH.     

OPTIMIZATION OF GLYCEROL EFFECT ON THE MECHANICAL PROPERTIES AND WATER VAPOR PERMEABILITY OF WHEY PROTEIN-METHYLCELLULOSE FILMS

Biopolymer films and coatings are generally designed using biological materials such as proteins, polysaccharides, lipids and their derivatives. The use of plasticizers is also required to improve the mechanical properties (tensile strength and elongation) of the films. For application of films to food systems, it is important for the developed films to possess favorable mechanical and permeability characteristics. Therefore, knowledge of optimum conditions where the water vapor permeability (WVP) is minimized while the mechanical properties are enhanced would be significant depending on the application of the edible films. In this study, the effects of glycerol, as a plasticizer, and methylcellulose (MC) ratios on WVP and mechanical properties of the whey protein films were investigated. Optimum properties of edible films were obtained by applying the complex method optimization algorithm to this multiobjective function problem, and glycerol to total polymer ratio (MC and whey protein concentrate [WPC]) of 0.356 and 0.45 was found for the films with MC : WPC ratios of 0.3 and 0.8, respectively. With respect to the results of this study, it might be concluded that optimum conditions for different edible film‐forming agents can be determined via the use of a good experimental design.     

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.     

RHEOLOGICAL AND PHYSICOCHEMICAL PROPERTIES OF DERIVATIZED WHEY PROTEIN CONCENTRATE POWDERS

ABSTRACT

The gelling ability of whey proteins provides important textural and water holding properties in many foods. However, because many products cannot be heated to the temperature needed for thermal gelation of whey proteins, cold-set gelation of whey proteins could be very advantageous to the food industry. A derivatization procedure for the production of a cold gelling whey protein isolate (WPI) consisting of protein hydration, pH adjustment, thermal gelation, freeze drying, and milling was applied to three commercial whey protein concentrates (WPC). The resulting derivatized WPC powders were reconstituted in water and evaluated through a range of rheological and physical property studies. The effects of temperature, concentration, and shear on viscosity as well as water holding capacity and intrinsic viscosity were assessed. Although the composition of the starting materials influenced the functionality of the final derivatized powders, all samples exhibited a dramatic increase in thickening and water holding ability. All samples were able to form cold-set weak gel structures suitable for contributing viscosity and texture to a wide range of food systems.     

IMPROVEMENT OF PHYSICAL PROPERTIES OF NONFAT FERMENTED MILK DRINK BY USING WHEY PROTEIN CONCENTRATE

The use of whey protein concentrate (WPC) for the improvement of physical properties of nonfat fermented milk drink was investigated. Drinks were prepared from nonfat milk powder and WPC at different proportions. Rheological properties, serum separation and particle size of the drinks were measured. The effect of WPC on the physical properties of the drinks was evaluated by comparison with those of commonly used stabilizers, including propylene glycol alginate and locust bean gum. WPC addition caused an increase in the consistency coefficient and thixotropy and a decrease in the particle size of the samples. There was no serum separation in the sample with 2% WPC. Large unstable aggregates were observed in the sample with 3% WPC, which also exhibited the highest serum separation. WPC up to a level of 2% positively influenced the physical properties of nonfat fermented milk drink similar to stabilizers.

PRACTICAL APPLICATIONS

Fermented milk drinks are consumed especially for their beneficial health effects. Physical properties of fermented milk drinks influence their quality and consumer acceptability. Hydrocolloid stabilizers are used for the improvement of physical properties of fermented milk products. Whey protein concentrates (WPC) with high protein content can be used to substitute hydrocolloid stabilizers. In this study, the effect of the addition of WPC with 75% protein in place of a part of the nonfat milk powder on the physical properties of nonfat fermented milk drink with 6% dry matter was investigated. Use of an appropriate level of WPC was found to be important for obtaining a desirable effect on the physical properties of nonfat fermented milk drink. The effect of WPC was found to be comparable to those of commonly used hydrocolloid stabilizers. Use of WPC also enhances the nutritional value of the product as whey proteins have a high biological value.     

EFFECT OF FERMENTED WHEY PROTEIN CONCENTRATE ON TEXTURE OF IRANIAN WHITE CHEESE

The influence of fermented whey protein concentrate (FWPC) added before and after formation of cheese curd on the textural characteristics of Iranian white cheese was studied. The FWPC, prepared from whey obtained during cheese making, was added at different levels 5, 10, 15 and 20% (v/v) after (A) or before (B) cheese curdling. The changes in rheological parameters of cheeses were determined before and after 1 month of ripening. It was found that both incorporation level and stage of addition of FWPC (A and B) caused significant effects on texture profile analysis of cheeses. Increasing the level of FWPC in B group, except samples containing 10% FWPC, in contrast with A cheeses led to considerable increase in moisture and decrease in hardness and chewiness. Samples containing more than 15% FWPC had undesirable texture and were too soft. All experimental cheeses exhibited a decline in values for each rheological parameter after 1 month of ripening.

PRACTICAL APPLICATIONS

Perhaps the biggest story in the dairy industry in the past couple of decades has been the rise of new applications for whey and whey proteins. Once considered a waste product in the cheese manufacturing process, whey and whey protein products today are used for a wide range of functional and nutritional properties. In the cheese industry, particularly in soft cheese varieties, whey proteins have shown good applications to replace caseins as they act as fat replacer and bind more water than caseins, which results in softer cheeses. Therefore, this study was attempted to investigate the impact of fermented whey protein concentrate on textural attributes of Iranian white cheese.     

ELECTROSTATIC EFFECTS ON PHYSICAL PROPERTIES OF PARTICULATE WHEY PROTEIN ISOLATE GELS

Physical properties of particulate whey protein isolate gels formed under varying electrostatic conditions were investigated using large strain rheological and microstructural techniques. The two treatment ranges evaluated were adjusting pH (5.2‐5.8) with no added NaCl and adjusting the NaCl (0.2‐0.6 M) at pH 7. Gels (10% protein w/v) were formed by heating at 80C for 30 min. The large strain properties of fracture strain (γ_f), fracture stress (σ_f), and a measure of strain hardening (R_0.3) were determined using a torsion method. Gel microstructure was evaluated using scanning electron microscopy (SEM) and gel permeability (B_gel). Overlaying σ_f and γ_f curves for pH and NaCl treatments demonstrated an overlap where gels of equal σ_f and γ_f could be formed by adjusting pH or NaCl concentration. The high fracture stress (σ_f～ 23 kPa and γ_f～ 1.86) pair conditions were pH 5.47 and 0.25 M NaCl, pH 7.0. The low fracture stress (σ_f～ 13 kPa and γ_f～ 1.90) pair conditions were pH 5.68 and 0.6 M NaCl, pH 7.0. The 0.25 M NaCl, pH 7 treatment demonstrated higher R_0.3 values than the pH 5.47 treatment. When the sulfhydryl blocker n‐ethylmaleimide was added at 2 mM to the 0.25 M NaCl, pH 7 gel treatment, its rheological behavior was NSD (p>0.05) to the pH 5.47 gel treatment, indicating disulfide bond formation regulated strain hardening. Altering surface charge or counterions, and disulfide bonding, was required to produce gels with similar large strain rheological properties. An increase in gel permeability coincided with an increase in pore size as observed by SEM, independent of rheological properties. This demonstrated that at the length scales investigated, microstructure was not linked to changes in large strain rheological properties.     

EXTRUDED CORN MEAL AND WHEY PROTEIN CONCENTRATE: EFFECT OF PARTICLE SIZE

Blends of whey protein concentrate (WPC) and corn meal, which were separated into four particle fractions (residual on a #30 screen, #40 screen, #60 screen and through a #60 screen), were extruded at two moisture conditions (23 and 28%) to determine the effects of particle size on the extrudate properties. Smaller particle size fractions exhibited increased solubility and significantly higher viscosity both with and without added protein. When WPC was added to the corn meal, a large reduction in paste viscosity was observed regardless of the particle size. The blend with similar particle size distributions of corn meal and WPC had a significantly higher viscosity than the other blends. The expansion ratio, porosity and breaking strength of this blend, when extruded at the lower moisture content, were improved to the extent that they behaved similarly to extrudate made from corn meal alone.     

EFFECT OF ENZYMATIC HYDROLYSIS ON SOME FUNCTIONAL PROPERTIES OF WHEY PROTEIN

A study was undertaken to further elucidate the functional properties of whey protein with respect to foaming and emulsifying capacities and to observe the effect of enzymatic hydrolysis on these properties. Emulsion capacity decreased as proteolysis continued suggesting there is an optimum mean molecular size of the proteins involved which is lower than that of casein. Heat treatment of the reconstituted protein concentrate was necessary for foam stability; specific volume and foam stability increased directly with temperature of heating. Re effect of pH on whippability, data indicate that the greater the net charge the greater the tendency to foam. A limited amount of hydrolysis appears desirable to increase foaming but greatly decreases foam stability.     

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.     

THE EFFECT OF CASEINOMACROPEPTIDE AND WHEY PROTEIN CONCENTRATE ON STREPTOCOCCUS MUTANS ADHESION TO POLYSTYRENE SURFACES AND CELL AGGREGATION

Caseinomacropeptide (CMP) from bovine, ovine and caprine milk and whey protein concentrate (WPC) were both evaluated for adhesion inhibition of Streptococcus mutans to polystyrene surface and cell aggregation. Adhesion inhibition by the CMPs and WPC at 1 mg/mL was higher than 84%. The CMPs and WPC caused aggregation of S. mutans cells at low concentrations. These findings suggest the application of these milk derived proteins as potential dental caries inhibitors and for possible food application uses.     

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.     

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.