Polyphenol oxidase (PPO) needs to be inactivated to control the enzymatic browning which is undesirable in fruits and vegetables industry.... Show morePolyphenol oxidase (PPO) needs to be inactivated to control the enzymatic browning which is undesirable in fruits and vegetables industry. Enzymes have substrateorigin- specificity, and thus the functionality and inactivation properties of PPO varies depending on the source of enzyme, properties of food matrix, method of treatment applied as well as measurement techniques. Therefore, the result from one food cannot be extrapolated to another food, and more research is needed to understand the behavior of PPO in different processing conditions. In this study, thermal inactivation of PPO in potato, avocado and apple was studied at four different temperatures (50, 60, 70 and 80 °C). The treatment time varied from 1 to 60 min, depending upon the temperature used. The level of inactivation was deduced by residual enzyme activity which was assayed by spectrophotometric methods in two different substrates, pyrocatechol and 3,4- dihydroxyphenylalanin (DOPA) using an ELISA plate reader. The degree of PPO inactivation achieved in potato and apple extracts was higher using pyrocatechol as the substrate than using DOPA, where it was similar for both substrates in case of avocado. Inactivation kinetics was studied in terms of rate constant k, D values and activation energy. The inactivation rate followed the first order kinetics and higher dependency on treatment time was observed at higher temperatures. Biphasic inactivation was observed in case of apple PPO, where activation of enzyme was observed at low temperature (50 °C). In conclusion, level of PPO inactivation was dependent on the degree of the thermal treatment, source of PPO and substrate used for enzyme determination. M.S. in Food Safety and Technology, July 2011 Show less
