Using isothermal heating, inactivation of lactoperoxidase (LPO) in goat, sheep and cow milk was studied in the temperature range of 70-77 degrees C. Kinetic and thermodynamics studies were carried out at different time-temperature combination in order to evaluate the suitability of LPO as marker for the heat-treatment of milk and dairy products from different species. The thermal inactivation of LPO followed the first-order kinetics. D- and k-values decreased and increased, respectively with increasing temperature, indicating a more rapid LPO inactivation at higher temperatures. The influence of temperature on the inactivation rate constant was quantified using the Arrhenius and thermal death time models. The corresponding z-values were 3.38 +/- 0.013, 4.11 +/- 0.24 and 3.58 +/- 0.004 degrees C in goat, sheep and cow milk, respectively. Activation energy values varied between milk species with 678.96 +/- 21.43 kJ mol(-1) in goat milk, 560.87 +/- 28.18 kJ mol(-1) in sheep milk and 641.56 +/- 13.12 kJ mol(-1) in cow milk, respectively. (C) 2012 Elsevier Ltd. All rights reserved.