Thiocyanate content and lactoperoxidase activity of individual cow's milk of different breeds were determined, and the effects of different lactoperoxidase system (LP-s) activation strategies were compared. Lactoperoxidase activity varied significantly between Friesian and both Ayrshire and Tanzania Short Horn Zebu (TSHZ), but differences between Ayrshire and TSHZ were not significant. There was no significant variation in SCN− content between breeds. The LP-s was activated using three strategies based on SCN−: namely; equal concentrations of SCN− and H2O2 (7:7, 10:10, 15:15 mg/l), excess SCN− concentrations (15:10, 20:10, 25:10 mg SCN−:H2O2/l), and excess H2O2 concentrations (10:15, 10:20, 10:25 mg SCN−:H2O2/l), plus a fourth strategy based on I− (15:15 mg I−:H2O2/l). The keeping quality (KQ) was assessed using pH, titratable acidity, clot on boiling and alcohol stability tests. All activation strategies enhanced the shelf life of milk (typically increasing KQ from around 10 to around 20 h), but it was clear that the effectiveness of the LP-s depends on the type and concentrations of the activators of the system. The LP-s activated using I− as an electron donor was more effective than the LP-s activated using SCN− as an electron donor, increasing the KQ by a further 6–8 h compared with SCN−.
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