Thermal inactivation kinetics of polyphenol oxidase in Tea (Camellia sinensis)

Abstract

Green teas are rich in catechins. Catechins are prone to oxidation. The enzyme poljqjhenol oxidase present in tea leaves mediates the oxidation of the catechins. Therefore, inactivation of polyphenol oxidase (PPO) is one of the andst steps in green tea manufacture. This is primarily done by heating the freshly harvested tea leaves and the process step is commonly referred to as 'fixing' in the tea industry. Various kinetic models for thermal inactivation of PPO were assessed. These included the first order model, fractional model, series model and the two traction model. The "two-fi-action" model was found to explain the thermal inactivation kinetics data of PPO (R^>0.99) in the tea leaves. Kinetic parameters corresponding to both the heatlabile and the heat-resistant fractions of the enzyme were established from the model. It was found that variation in rate constants with temperature was not governed by Arrhenius relationship