Effect of pH on the thermal denaturation of whey proteins in milk

The effect of pH on thermal denaturation of four main whey protein fraction s in skim milk was examined by gel permeation FPLC. On heating skim milk, a t 80 degrees C for 0.5-20.0 min over the pH range 5.2-8.8, the extent of de naturation, based on loss of solubility at pH 4.6, increased with heating t ime and was usually in the order immunoglobulins > serum albumin/lactoferri n > beta-lactoglobulin > alpha-lactalbumin. Rates of denaturation of the im munoglobulins and the serum albumin/lactoferrin fraction were highest at th e lower end of this pH range, whereas these of beta-lactoglobulin and alpha -lactalbumin increased over most of the pH range. The effects of pH, additi on of Ca, and reduction of disulfide bonds on the rates of the unfolding an d aggregation stages of denaturation are discussed.