Proteolysis, protein distribution and stability of UHT milk during storageat room temperature

Proteolytic degradation and distribution of caseins and whey proteins betwe en the soluble and colloidal phases were studied in six batches of commerci al UHT milk (three skim and three whole milks) during storage at 25+/-2 deg rees C. For that purpose, at 30 day intervals, milk samples were ultracentr ifuged and the pellets and supernatants analysed by capillary electrophores is and SDS-PAGE. Samples were also visually examined for signs of gelation. Extensive proteolytic degradation of the micellar fractions and severe cha nges in the electrophoretic pattern of the proteins present in the serum fr actions were observed in all the batches. A higher proportion of denatured whey proteins not attached to the micelle surface was found in the skim mil li samples as compared with the whole milk samples that could provide less resistance against gelation. In addition to beta-Lg, para-kappa-casein was also found in the serum fraction. A high proteolytic activity against kappa -casein could be responsible for the hydrolysis of serum-liberated kappa-ca sein or could have enhanced the Liberation of beta-Lg-para-kappa-casein com plexes through proteolysis of micellar kappa-casein. (C) 1999 Society of Ch emical Industry.