Background: Lactoperoxidase (LPO) is one of the most heat-stable enzymes in milk and its inactivation has been proposed for monitoring thermal processes. The aim of this study was to provide information on activity and thermal inactivation behavior of LPO in Iranian cow and buffalo milk and whey.

Methods: Sixty cow and buffalo milk samples were collected. The LPO activity was measured using spectrophotometer at 436 nm using a multimode microplate reader. Thermal inactivation behavior of LPO in milk and whey samples was investigated at temperatures 65, 70, 75, and 80 ^°C, using glass capillaries for quick temperature transfer. Data were analyzed using SPSS software (Chicago, IL, v. 16.0).

Results: LPO activity was slightly, but not significantly, higher in buffalo milk than in cow milk, where its activity was 4.15±0.13 U/ml and 4.02±0.1 U/ml in buffalo and cow milk, respectively. LPO activities in cow and buffalo whey were 16-19% lower than the respective values in milk, on average, 3.39±0.1 U/ml in buffalo whey and 3.36±0.08 U/ml in cow whey. No significant differences (p>0.05) were observed between thermal stabilities of LPO in both milk types. In addition, at all the tested temperatures, LPO was heater labile in whey than milk, in both milk types.

Conclusion: There were some variations in LPO behavior against thermal processing in cow and buffalo milk and whey. So, these findings could be helpful in further studies about monitoring thermal processes in dairy industries.