Thermal inactivation of peroxidase (POD) and polyphenol oxidase (PPO) in both pomegranate arils crude enzyme extract and fresh juice was investigated. The optimum conditions for reactions were studied using a mixture of guaiacol and H2 O2 as substrate for POD and pyrogallol for PPO. The experimental work indicated that optimum pH for both enzymes was 7.0; meanwhile optimum temperature was 30°C for POD and 25°C for PPO. Michaelis-Menten constant (Km) values for POD were 8.33 and 8.00 mM for guaiacol and H2 O2, respectively. The Km value was 5.88 mM pyrogallol for PPO. Thermal inactivation results revealed that the inactivation kinetics followed a monophasic first-order model. Activation energies (Ea) were 74.68 and 112.97 kJ/mol for POD and PPO, respectively. Therefore, POD was more heat-stable than PPO. This result is very useful to optimize pomegranate processing (canning or freezing), which represents the most important food industries in many tropical and subtropical regions. PRACTICAL APPLICATIONS: Pomegranate has been attracted more interest due to its antioxidant and nutritional values. For industrial applications, there is a growing interest to obtain pomegranate products such as juice, jams, food supplements, etc. It is well established that the residual activities of endogenous enzymes in either raw materials or processed products may cause loss of quality during storage. Inhibition of enzymatic browning is an important factor to maintain pomegranate quality. This work offers a better insight of characterization of browning enzymes and their thermosatbility, which will be useful to control the possible browning of pomegranate arils during processing and storage. In addition, the results of this study is very important in pomegranate processing where it showed a higher temperature with shortened time can be applied.
Keywords: optimum conditions; peroxidase; polyphenol oxidase; pomegranate arils; thermal inactivation.
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