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 degrees 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 P-lactoglobulin (beta-LG). Overall, heating at low pH (3) caused unfolding of proteins and fragmentation due to partial acid hydrolysis and thereby exposed. beta-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 beta-LG but may have an effect in combination with pH or temperature. Overall, heating P-LG solutions to 120 degrees C at pH 5 with shearing (100-1,000 s(-1)) resulted in minimal antigenicity. Structural modifications of beta-LG via denaturation or disulfide- or thiol-mediated interactions can either enhance or decrease its antigenicity.