Effect of plasmin and somatic cell enzymes on proteolysis in aseptic starter and rennet free model cheeses

Aseptic, rennet and starter free (ASRF) cheeses were prepared from milk of low and high SCC. The coagulant used, pepsin, was inactivated by a high pH cooking stage during manufacture, thimerosal was added to prevent bacterial growth and gluconic acid-delta-lactone was used to acidify the curds to a range of pH values. Curds prepared from high SCC milk had higher overall le vels of proteolysis than low SCC curds over a range of pi-is from 6.4 to 4. 8 and had accelerated breakdown of beta- and alpha(s1)-caseins. The pattern of proteolysis was not consistent with a system dominated by cathepsin D a nd plasmin alone. The mastitic curds also had an accumulation of hydrophobi c bitter material over 10 weeks ripening at 11 degrees C, which, together w ith the accelerated breakdown of alpha(s1)-casein may indicate a role for s omatic cell proteinases in influencing cheese ripening, and flavour and tex ture of cheese in particular. This may be linked to similar problems associ ated with cheese prepared from late lactation milks of elevated SCC.