ACTA ALIMENTARIA VOL. 12 (A QUARTERLY OF THE COMMITTEE ON FOOD SCIENCE OF THE HUNGARIAN ACADEMY OF SCIENCES, 1983)
1983 / 1. sz. - VÁMOS-VIGYÁZÓ, L.-NÁDUDVARI-MÁRKUS, V.: Inactivation of polyphenol oxidase and depletion of o-dihydroxy phenol content during the enzymatic browning reaction of fruit tissues
Acta Alimentaria, Vol. 12 (1), pp. 1-9 (1983) INACTIV ATI ON OF POLYPHENOL OXIDASE AND DEPLETION OF O-DIHYDROXY PHENOL CONTENT DURING THE ENZYMATIC BROWNING REACTION OF FRUIT TISSUES L. VÁMOS-VIGYÁZÓ and V. NÁDUDVARI-MÁRKUS (Received: 5 June 1981; accepted: 15 July 1981) In order to study enzyme inactivation and substrate depletion during the browning reaction of fruit tissues, the changes in these variables were followed in aerated pulps of two apricot and two apple cultivars of different mass-related polyphenol oxidase activities and o-dihydroxy phenol contents. Although enzyme activity decreased from the beginning of aeration, in the majority of samples substrate concentration reached levels near to depletion while polyphenol oxidase activity was still considerable. The results obtained with apricots suggested that not all the o-dihydroxy phenols present in this fruit were substrates of polyphenol oxidase. Enzyme inactivation related to unit decrease in o-dihydroxy phenol content was more marked in the samples of higher initial polyphenol oxidase activities and lower o-dihydroxy phenol contents and vice versa. This means that the reaction inactivation of polyphenol oxidase was inversely related to product formation. Consequently, under the given conditions, enzyme inactivation during the polyphenol oxidase-catalyzed oxidation of o-dihydroxy phenols cannot be caused by quinone binding by the enzyme molecule. In an earlier study (VÁMOS-VIGYÁZÓ et al., 1977) carried out with fruit homogenates, the ratio of mass-related polyphenol oxidase (PPO) activity and the concentration of its endogenous substrates was found to indicate which of these factors determines the initial browning rate of the product. In fruit of relatively high polyphenol content and low mass-related PPO activity (e.g., the apple cultivars Jonathan and Golden Delicious) (VÁMOSVIGYÁZÓ et al., 1980) the latter variable proved to play the primary role; in most of the apricot cultivars studied, where the situation was reversed (GAJZÁGÓ et al., 1979), browning rate was related to polyphenol concentration. It was assumed that in the first case reaction inactivation of the enzyme occurred while substrate was still present (WALKER, 1964; WHITAKER, 1972; PADRÓN etal., 1975). Thus, necessarily, mass-related enzyme activity would be the limiting factor in the browning reaction. In the second case total substrate depletion was assumed to take place prior to enzyme inactivation, thus the reaction would be limited by substrate concentration. In order to support these considerations by experimental evidence, model experiments were carried out with apple and apricot homogenates of different ratios of mass-related PPO activity and endogenous polyphenol