ENZYMATIC BROWNING OF PEACHES: EFFECT OF GIBBERELLIC ACID AND ETHEPHON ON PHENOLIC COMPOUNDS AND POLYPHENOLOXIDASE ACTIVITY

Abstract

ABSTRACTFoliar sprays of gibberellic acid and ethephon applied to Redhaven peach trees at 21 and 46 days after bloom caused a reduction of enzymatic browning in mature fruit tissue. A replicate from each treatment was analyzed by two‐dimensional thin‐layer chromatography and polyacrylamide disc gel electrophoresis. Twenty‐one polyphenolic compounds were separated. Eight were oxidized by PPO, and were tentatively identified as four chlorogenic acid isomers, three leucoanthocyanidins, and catechin. No differences in qualitative distributions of phenolic compounds were observed which would account for the inhibition of browning in peach tissue. Polyacrylamide disc gel electrophoresis of peach PPO preparations showed the presence of up to 11 multiple forms displaying activity toward catechol. The bands had different substrate specificities and were present in different amounts, but PPO from peaches treated 21 days after bloom appeared to have a catechol reactive band not present in untreated peaches or peaches treated 46 days after bloom. One band from peaches treated 46 days after bloom with 150 ppm ethephon appeared to have decreased substrate specificity toward pyrogallol. Crude PPO preparations from untreated fruit and fruit receiving the 46‐day treatments oxidized o‐dihydroxyphenols only, and the relative PPO activities varied with treatment. These PPO preparations exhibited two pH optima; pH 4.4 and 6.2 for untreated and GA‐treated peaches (46‐day treatment), and pH 4.4 and 6.6 for peaches treated with ethephon (75 or 1.50 ppm, 46‐day treatment). PPO from the treated peaches had a lower proportion of total activity at pH 4.4 than PPO from untreated peaches.