Interactions between whey proteins and salivary proteins as related to astringency of whey protein beverages at low pH

Whey protein beverages have been shown to be astringent at low pH. In the present study, the interactions between model whey proteins (beta-lactoglobulin and lactoferrin) and human saliva in the pH range from 7 to 2 were investigated using particle size, turbidity, and zeta-potential measurements and sodium dodecyl sulfate-PAGE. The correlation between the sensory results of astringency and the physicochemical data was discussed. Strong interactions between beta-lactoglobulin and salivary proteins led to an increase in the particle size and turbidity of mixtures of both unheated and heated beta-lactoglobulin and human saliva at pH similar to 3.4. However, the large particle size and high turbidity that occurred at pH 2.0 were the result of aggregation of human salivary proteins. The intense astringency in whey protein beverages may result from these increases in particle size and turbidity at these pH values and from the aggregation and precipitation of human salivary proteins alone at pH <3.0. The involvement of salivary proteins in the interaction is a key factor in the perception of astringency in whey protein beverages. At any pH, the increases in particle size and turbidity were much smaller in mixtures of lactoferrin and saliva, which suggests that aggregation and precipitation may not be the only mechanism linked to the perception of astringency in whey protein.