MONITORING OF HEAT-INDUCED PROTEOLYSIS IN MILK AND MILK-RESEMBLING SYSTEMS

Peptide mapping from the soluble fractions of skimmed milk and a milk- resembling system, obtained either by treatment with trichloroacetic a cid (TCA, 40 and 120 g/L) or by adjusting the pH to 4.6, were analyzed by RP-HPLC with UV (205, 214, and 280 nm) and fluorescent; detection (excitation at 280 and 270 nm and emission at 340 and 310 nm). Two pep tides (p21 and p25), both soluble in 120 g/L TCA, were chosen for foll owing the extent of the heat-induced proteolysis in milk and milk-rese mbling systems. Both peptides were absent in skimmed raw milk, but wer e detected in low amounts in Na-caseinate/lactose solution. The rate o f formation of p21 and p25 peptides could be fitted to zero-order kine tics. The p25 peptide was formed more rapidly in skimmed milk than in the Na-caseinate/lactose system. As for the p21 peptide, other factors apart from temperature and heating time should be considered for unde rstanding its thermal behavior. Possibly, p21 and p25 peptides could b e applied for assessing previous industrial processing.