The influence of somatic cell count on the heat stability of bovine milk plasmin activity

Abstract

Abstract The heat stability of bovine milk plasmin activity and the role of plasminogen activators in milk of low and high somatic cell count (SCC) were examined, with or without KIO3 addition. The inactivation of plasmin was a first-order reaction and Arrhenius plots showed two-stage inactivation kinetics. Plasmin was more heat stable in high SCC milk than low SCC milk after low temperature treatments such as thermisation and pasteurisation, but less stable in high SCC milk under UHT-range thermal treatments. The addition of KIO3 to low SCC milk before heating resulted in considerably greater heat stability of plasmin at all heating temperatures. The activation energy, Ea, for the inactivation reaction in the temperature range 63–110°C was estimated as 52.75 and 74.44 kJ mol-1 for low and high SCC milk, respectively. The Ea for inactivation of plasmin in the temperature range 110–138°C was estimated as 22.03 and 24.70 kJ mol-1 for low and high SCC milk, respectively. The high SCC milk containing KIO3 showed evidence of considerable plasminogen activator activity, apparently leading to activation of plasminogen during the heating process itself. Overall, without the inactivating influence of denatured β-lactoglobulin, plasmin activity is extremely heat stable in native milk systems and plasminogen activators derived from somatic cells appear to be likewise very heat stable and active during heating processes.