The objective of this study was to correlate the plasmin activity and the concentrations of casein fractions in ultra-high-temperature (UHT) milk manufactured in a dairy plant in the State of Sao Paulo, Brazil. Raw milk was pasteurized (72-76 ºC, 15-20 seconds), followed by direct steam injection into the milk (132-136 ºC, 34 seconds), then homogenized and aseptically packaged into cartons. Four replicates of the UHT milk were analyzed for the plasmin activity and casein fractions after 10, 30, 60, 90 and 120 days of storage. Plasmin activity significantly increased in the UHT milk during storage and was negatively correlated with the concentration of αs1-casein. Plasmin is resistant to milk sterilization by the UHT process, and increases proteolysis of the UHT milk as a consequence of αs1-casein degradation.
Plasmin; Caseins; UHT milk; Proteolysis
