Changes In Whey Proteins Research Articles

Physicochemical changes in whey protein concentrate texturized by reactive supercritical fluid extrusion

The mechanisms of interactions in whey protein concentrate (WPC) texturized by reactive supercritical fluid extrusion and pH modifications were evaluated in terms of protein solubility in different extraction buffers, electrophoresis, free sulfhydryl (SH) groups, and apparent viscosity. The soluble protein content and free SH groups of the texturized WPC (tWPC) produced at pH 2.89 decreased by ∼20% and 16% relative to the unextruded control. It was completely soluble in the presence of urea and SDS, indicating the importance of non-covalent interactions in maintaining the structure of this product. Its dispersion (20% w/w) yielded a creamy texture with a particle size in the micron-range (mean diameter ∼5 μm) and contributed ∼258 times higher viscosity compared to the unextruded control. The tWPC produced at pH 8.16 was soluble only in the presence of a reducing agent. It yielded a grainy texture with a high proportion of large particles due to an extensive aggregation via intermolecular disulfide formations.

Changes and Roles of Secondary Structures of Whey Protein for the Formation of Protein Membrane at Soy Oil/Water Interface under High-Pressure Homogenization

The conformational changes of whey proteins upon adsorption at the soy oil/water interface were investigated using Fourier transform infrared (FT-IR) spectroscopy. Significant changes were observed in the bands assigned to beta-sheets and alpha-helix structures following the adsorption of proteins at the oil/water interface. The remaining interfacial proteins after Tween 20 desorption revealed small changes in beta-sheet and alpha-helical structures, whereas in the desorbed whey proteins the unordered structures largely increased, and beta-sheet structures almost disappeared. These FT-IR results provide important knowledge about the conformational modifications in whey proteins occurring upon adsorption at the oil/water interface. Finally, specific conformational changes are necessary to stabilize emulsions: adsorption-induced unfolding, increase in alpha-helical structures to establish interactions with the oil phase, and aggregation between adsorbed whey proteins to form protein membranes. Moreover, the structural changes in whey protein adsorbed at the oil/water interface under high-pressure homogenization are irreversible.

Cross-linking and rheological changes of whey proteins treated with microbial transglutaminase.

Modification of the functionality of whey proteins using microbial transglutaminase (TGase) has been the subject of recent studies. However, changes in rheological properties of whey proteins as affected by extensive cross-linking with TGase are not well studied. The factors affecting cross-linking of whey protein isolate (WPI) using both soluble and immobilized TGase were examined, and the rheological properties of the modified proteins were characterized. The enzyme was immobilized on aminopropyl glass beads (CPG-3000) by selective adsorption of the biotinylated enzyme on avidin that had been previously immobilized. WPI (4 and 8% w/w) in deionized water, pH 7.5, containing 10 mM dithiothreitol was cross-linked using enzyme/substrate ratios of 0.12-10 units of activity/g WPI. The reaction was carried out in a jacketed bioreactor for 8 h at 40 degrees C with continuous circulation. The gel point temperature of WPI solutions treated with 0.12 unit of immobilized TGase/g was slightly decreased, but the gel strength was unaffected. However, increasing the enzyme/substrate ratio resulted in extensive cross-linking of WPI that was manifested by increases in apparent viscosity and changes in the gelation properties. For example, using 10 units of soluble TGase/g resulted in extensive cross-linking of alpha-lactalbumin and beta-lactoglobulin in WPI, as evidenced by SDS-PAGE and Western blotting results. Interestingly, the gelling point of WPI solutions increased from 68 to 94 degrees C after a 4-h reaction, and the gel strength was drastically decreased (lower storage modulus, G'). Thus, extensive intra- and interchain cross-linking probably caused formation of polymers that were too large for effective network development. These results suggest that a process could be developed to produce heat-stable whey proteins for various food applications.

The influence of high temperatures on milk proteins

High temperatures Induce certain changes in milk constituents, but the degree of these changes depends on both the temperature and time of heat treatment. The most pronounced changes take place in milk proteins. The forewarming of milk causes an increase in acidity, the precipitation of soluble Ca-phosphate, whey protein denaturation and coagulation, as well as the interaction with casein micelles, the Maillard browning reaction, the dephosphorylation of casein, the hydrolysis of casein micelles, changes in whey proteins, an extension of the rennet coagulation time and an exchange of the rheological properties of the acid and rennet casein gels, changes in the zeta-potential and casein micelle hydration, the interaction between the milk proteins and proteins of milk fat globule membrane.

Process-induced changes in whey proteins during the manufacture of whey protein concentrates

Abstract Samples of cheese whey or acid casein whey obtained from commercial plants during the different stages of whey protein concentrate (WPC) manufacture were analyzed for protein composition and the extent of protein aggregation. Protein composition was determined by size exclusion chromatography (SEC) and electrophoresis, while the degree of protein aggregation was determined through the changes in molecular weight distributions monitored by SEC combined with multi-angle laser light scattering. The results show that there were some differences between the compositions of protein between the two types of wheys with the acid casein whey also containing lower proportions of “soluble” aggregates than the cheese whey. Ultrafiltration/diafiltration processes caused a removal of the non-protein, low molecular weight components, but had no significant effect on protein composition and aggregation. Evaporation and subsequent spray drying of the ultrafiltered retentates caused no significant changes in any of the whey protein components. Differences in functionality of WPC products are probably more related to modifications of proteins and other components caused by the processes that are used in cheese or casein manufacture rather than to the WPC manufacturing process.

Effect of heat treatment on camel milk proteins with respect to antimicrobial factors: a comparison with cows' and buffalo milk proteins

Camel, cow and buffalo skim milk samples were heated at 65, 75, 85 and 100°C for 10, 20 and 30 min. Presence and identity of whey proteins (WPs) were monitored using SDS-PAGE technique. Changes in activities of antimicrobial factors were measured. Heat-induced changes of WPs increased with increasing temperature and time of heating; they were more pronounced in buffalo and cow milk than in camel milk. Camel WPs were markedly more heat resistant than their counterparts in cow and buffalo milk. Among the WPs, the order of heat resistance found was: α-lactalbumin > β-lactoglobulin > serum albumin. Camel milk contained significantly ( P⩽0.01) higher concentrations of lysozyme (LZ), lactoferrin (LF) and immunoglobulin G (IgG) than cow and buffalo milk. Heating milk at 65°C/30 min had no significant effect on LZs and LFs, however, loss of activity of IgGs was significantly ( P⩽0.01) affected in the three kinds of milk. The whole activity of IgG in cow and buffalo milk was lost at 75°C/30 min versus 68.7% in loss activity of camel IgG. The entire activity of LFs was lost at 85°C/30 min in all kinds of milk, however, at this level of temperature, the activity losses of LZs were 56, 74 and 81.7% for camel, cow and buffalo milk, respectively. Camel milk antimicrobial factors were significantly ( P⩽0.01) more heat resistant than cow and buffalo milk proteins. Among the antimicrobial factors, the order of heat resistance found was LZ > LF > IgG.

Heat-Induced Conformational Changes in Whey Protein Isolate and Its Relation to Foaming Properties

Heat-induced changes in the physicochemical properties of whey protein isolate (WPI) have been studied. WPI (5%) heated at 70 o C underwent rapid conformational changes within 1 min. The aperiodic structure content increased primarily at the cost of β-sheet structure. The hydrophobic character, as measured by changes in the pH-solubility profile and the solubility profile at pH 4.6 in NaCl solutions, of the protein surface increased. However, the surface hydrophobicity, as measured by the cis-parinaric acid binding method, decreased. In contrast, WPI (9%) heated at 90 o C did not exhibit significant changes in the secondary structure content

Quantitative densitometry of heat‐induced changes in whey proteins following ultrathin‐layer isoelectric focusing

AbstractThe effcient and rapid technique of ultrathin‐layer isoelectric focusing on 50 μm polyacrylamide gels was used for determination of heat‐induced changes of whey proteins (β‐lactoglobulin A and B as well as α‐lactalbumin) and a method for quantitative densitometry was developed. Improved reproducibility could be achieved by (i) introducing an internal standard (carbonic anhydrase), allowing for compensation for minor irregularities in gel composition, sample application or staining, (ii) running each sample in triplicate, and (iii) multiple scanning of each sample at different positions of the focusing track. Coefficients of variation of the integrated peak areas were approximately 3 % for β‐lactoglobulin A and B and about 6 % for α‐lactalbumin. Skim milk was heated in a pilot heating plant especially designed for reaction kinetic studies. Using the initial content of native whey proteins in each milk sample as a reference value, degrees of denaturation of more than 90 % could be determined for each of the three protein fractions. Results obtained from reaction kinetic studies revealed that denaturation of α‐lactalbumin was a first‐order reaction.

The Adsorption of Whey Proteins on the Surface of Emulsified Fat

Whey proteins adsorbed on fat globule surfaces during emulsification with coconut oil at pH 3 ~ 9 were examined. The amount of proteins adsorbed on the fat surface was dependent on the pH during emulsification. At any pH examined here, however, tightly-adsorbed proteins which were not extracted from the fat surface with urea or guanidine-HCl were 2 ~ 3 mg/m2. Marked selectivities in the adsorption of individual whey proteins were observed at any pH. No correlation between the adsorbabilities and the surface hydrophobicities of individual whey proteins was observed. Whey proteins adsorbed on the emulsified fat were much more easily digested with proteases compared to the native whey proteins, indicating that conformational changes of whey proteins occurred at the fat surface. The results suggested that conformational properties, such as flexibility of the structure, of whey proteins are important in the adsorption and possibly affect their emulsifying ability.

The adsorption of whey proteins on the surface of emulsified fat.

Whey proteins adsorbed on fat globule surfaces during emulsification with coconut oil at pH 3 ~ 9 were examined. The amount of proteins adsorbed on the fat surface was dependent on the pH during emulsification. At any pH examined here, however, tightly-adsorbed proteins which were not extracted from the fat surface with urea or guanidine-HCl were 2 ~ 3 mg/m2. Marked selectivities in the adsorption of individual whey proteins were observed at any pH. No correlation between the adsorbabilities and the surface hydrophobicities of individual whey proteins was observed. Whey proteins adsorbed on the emulsified fat were much more easily digested with proteases compared to the native whey proteins, indicating that conformational changes of whey proteins occurred at the fat surface. The results suggested that conformational properties, such as flexibility of the structure, of whey proteins are important in the adsorption and possibly affect their emulsifying ability.

Changes in Whey Proteins between Drying and Colostrum Formation

Changes in Whey Proteins between Drying and Colostrum Formation

Whey Protein Patterns of Milk from Cows with Experimentally Produced Mastitis

Summary Whey protein patterns were determined on milk samples from cows in which experimentally induced mastitis was being studied. In two trials in which the cows showed increased temperatures, decreased production, and grossly abnormal milk, there were marked changes in the whey protein patterns. In the third trial, the attempt to produce mastitis resulted in increased cell counts and CMT scores, but no other definite evidence of mastitis. The changes in the whey protein patterns of samples collected during this trial were slight. In the third trial, it appeared that increases in cell numbers and CMT scores were more sensitive than changes in whey proteins as indicators of inflammation of the mammary gland. Whey protein analysis may be useful in studying the physiological responses in attempts to experimentally induce mastitis under controlled conditions.