Effect of Disulfide Interactions and Hydrolysis on the Thermal Aggregation of β-Lactoglobulin

The roles of sulfhydryl/disulfide interactions and acid/pepsin hydrolysis on beta-lactoglobulin (beta-lg) thermal aggregation at acidic pH 3.35 and 2 were studied using rheology, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), transmission electron microscopy (TEM), and Western blotting. Pepsin promoted additional hydrolysis compared to the add-hydrolyzed control sample based on a 12% increase in free amino groups. Hydrolysis with pepsin also resulted in an increase in the apparent viscosity by 2 logs upon heating 8% beta-lg solutions at pH 3.35. Seemingly, hydrolysis promoted thermal aggregation of beta-lg, correlating well with viscosity increases. Large microgels were observed in heated pepsin hydrolysates using TEM, supporting the increased viscosities of these dispersions. During thermal aggregation (85 degrees C, 3 h) of beta-lg at pH 3.35, beyond the existence of limited disulfide interactions, add hydrolysis and noncovalent interactions more likely play a crucial role in defining the functionality of acidified powdered modified whey ingredients.