Influence of concentration of milk solids on the dissociation of micellar κ-casein on heating reconstituted milk at 120°C

Abstract

SummarySkim milks were prepared from skim milk powder at several concentrations between 10 and 25% total solids and portions were pH-adjusted to between pH 6·3 and 7·1 and heated at 120°C. After ultracentrifugation (88000 g for 90 min), the supernatants were analysed using gel electrophoresis to determine the concentrations of β-lactoglobulin, α-lactalbumin and κ-casein. The dissociation of κ-casein from the micelles was dependent on both the pH and the total solids content of milk before heating. Both higher pH (in the range 6·5–7·l) and higher concentration increased the extent of dissociation. A further series of samples were heated for 2–11 min at 120°C at pH 6·55. κ-Casein dissociation increased with concentration and with heating time. It was concluded that as the milk increased in concentration, the pH at which micellar κ-casein dissociated on heating was lowered.