Composition, physicochemical properties, and thermal inactivation kinetics of polyphenol oxidase from wax apple (Syzgium samarangense) juice

Abstract

Thermal treatment can reduce the microbial load and enzymatic activity, which is important to produce a safe and good quality product in the fruit juice industry. Hence, it is crucial to determine suitable thermal processing condition parameters based on the composition and thermal properties of enzymes present in fruit juice to avoid over-processing. The aim of this work was to determine the enzymatic inactivation kinetics of wax apple to obtain useful information for production of ready-to-drink wax apple juice. The wax apple juice prepared in the present study complied with Malaysia Food Regulations 1985 Regulation 235. The main sugars present in the wax apple juice are fructose and glucose, and traces of sucrose. High content of potassium was detected in the wax apple juice. In addition, wax apple juice contains a considerable amount of phenolic compounds. The thermal inactivation kinetics of polyphenol oxidase (PPO) followed the first order kinetic model. The activation energy, enthalpy changes, D88.4 °C, and z value of PPO obtained were 75.93 kJ/mol, 62.14 kJ/mol, 5.89 min, and 36.9 °C, respectively. In conclusion, the results evidenced that PPO which is more heat resistant than peroxidase, is a better enzyme inactivation indicator for the thermal treatment of wax apple juice. Therefore, PPO could be used as a heat treatment index for thermal processing that would be useful in designing thermal process for manufacturing of ready-to-drink wax apple juice.