Thermal inactivation kinetics of Rabdosia serra (Maxim.) Hara leaf peroxidase and polyphenol oxidase and comparative evaluation of drying methods on leaf phenolic profile and bioactivities

Inactivation kinetics of peroxidase and polyphenol oxidase in fresh Rabdosia serra leaf were determined by hot water and steam blanching. Activation energy (52.30 kJ mol(-1)) of polyphenol oxidase inactivation was higher than that (20.15 kJ mol(-1)) of peroxidase. Water blanching at 90 degrees C or steam blanching at 100 degrees C for 90 s was recommended as the preliminary treatment for the retention of phenolics. Moreover, comparative evaluation of drying methods on the phenolics profiles and bioactivities of R. serra leaf were conducted. The results indicated that only intact leaf after freeze drying retained the initial quality. The sun- and air-dried leaves possessed identical phenolic profiles. The homogenised leaf (after freeze-drying) possessed a lower level of phenolics due to enzymatic degradation. Good antioxidant activities were detected for the sun- and air-dried leaves. There was insignificant difference in anti-tyrosinase and anti-a-glucosidase activities among sun-, air-, and freeze-dried leaves. (C) 2012 Elsevier Ltd. All rights reserved.