Interaction between β-Casein and Whey Proteins As a Function of pH and Salt Concentration

The effectiveness of beta-casein as a chaperone in the aggregation of whey proteins was investigated. beta-Casein altered heat-induced aggregation as shown by a reduction in turbidity of p-lactoglobulin, a-lactalbumin, and bovine serum albumin (BSA) solutions. The pH of the mixtures greatly affected how much beta-casein reduced the turbidity of the solutions; the maximum reductions in turbidity were observed at pH 6.0. Reducing the pH decreased the effectiveness of beta-casein as a chaperone. An increase in ionic strength by the addition of NaCl or CaCl2 also decreased the effectiveness of the chaperone. The addition of CaCl2 had a larger effect than the addition of NaCl. The chaperone effect was seen at temperatures up to 145 degrees C. Differential scanning calorimetry (DSC) showed that beta-casein did not alter the denaturation temperature of p-lactoglobulin. The kinetics curves for loss of native protein and turbidity development showed that beta-casein did not function by slowing the aggregation process. It was concluded that beta-casein competes with whey protein in the aggregate process and the aggregates formed in the presence of beta-casein are smaller in size than those formed during whey protein self-aggregation. The formation of smaller aggregates gives rise to less turbid, more soluble protein solutions.