Denaturation of whey proteins as a function of heat, pH and protein concentration

Using state diagrams for predicting colloidal stability of whey protein beverages

A method for evaluating aspects of colloidal stability of whey protein beverages after thermal treatment was established. Three state diagrams for beverages (pH 3-7) were developed representing protein solubility, turbidity, and macroscopic state after two ultrahigh-temperature (UHT) treatments. Key transitions of stability in the state diagrams were explored using electrophoresis and chromatography to determine aggregation propensities of β-lactoglobulin, α-lactalbumin, bovine serum albumin, and glycomacropeptide. The state diagrams present an overlapping view of high colloidal stability at pH 3 accompanied by high solubility of individual whey proteins. At pH 5, beverages were characterized by poor solubility, high turbidity, and aggregation/gelation of whey proteins with the exception of glycomacropeptide. Stability increased at pH 6, due to increased solubility of α-lactalbumin. The results indicate that combinations of state diagrams can be used to identify key regions of stability for whey protein containing beverages.

Conformational changes of β-lactoglobulin induced by shear, heat, and pH-Effects on antigenicity

Structural modifications influence the immune-reactivity of food proteins. We investigated effects of pH (3, 5, 7), temperature (80, 100, 120°C), and shear (100, 500, and 1,000 s(-1)) on conformational changes (monitored by surface hydrophobicity, total thiol content, Fourier transform infrared spectroscopy, and gel electrophoresis) and their relation to antigenicity (determined by indirect ELISA) of β-lactoglobulin (β-LG). Overall, heating at low pH (3) caused unfolding of proteins and fragmentation due to partial acid hydrolysis and thereby exposed β-strands that contributed to appearance of some hidden epitopes, resulting in higher antigenicity. Heating at pH 5 and 7 decreased the allergenic response due to covalently bonded molecular polymerization and aggregation, which destroyed or masked some epitopes. Shear alone had no effect on the antigenic response of β-LG but may have an effect in combination with pH or temperature. Overall, heating β-LG solutions to 120°C at pH 5 with shearing (100-1,000 s(-1)) resulted in minimal antigenicity. Structural modifications of β-LG via denaturation or disulfide- or thiol-mediated interactions can either enhance or decrease its antigenicity.