Abstract:

The thermo-inactivation kinetic law of plasmin in milk was studied by heating high somatic cell count (HSCC) and low somatic cell count (LSCC) milk at 65 130 , respectively. Results revealed that plasmin inactivation kinetics in milk was in agreement with classic first-order equation. Plasmin activity decreased through heating at different temperatures. No significant difference of plasmin activity was observed after pasteurization at 65 85 (P 0.05), but plasmin activity of either HSCC or LSCC milk exhibited a significant difference through thermal treatments at ultra-high temperatures (P 0.05). The D value (the time for 90% plasmin inactivation) of HSCC milk was larger than that of LSCC milk below 110 ; however, the D-value was determined to be 53.75 s for HSCC milk and 58.94 s for LSCC milk at 130 , respectively. The apparent activation energy (Ea) for HSCC and LSCC milk was 65.76 and 57.26 kJ/mol at 65 95 , 22.12 and 21.48 kJ/mol at 95 130 , respectively. Therefore, no significant difference for plasmin activity is observed in high and low SCC milk with low temperature treatments (65 85 ) through pasteurization. Moreover, HSCC milk shows a higher stability than LSCC milk. In contrast, both HSCC and LSCC milk exhibit an obvious decrease in plasmin activity and no difference in thermostability through ultra-high temperature treatments.

Key words: HSCC milk , LSCC milk , plasmin, thermo-inactivation , kinetic , apparent activation energy