BROWNING POTENTIAL, PHENOLIC COMPOSITION, AND POLYPHENOLOXIDASE ACTIVITY OF BUFFER EXTRACTS OF PEACH AND NECTARINE SKIN TISSUE

The relationship of phenolic composition and polyphenoloxidase activity (PPO, E.C. 1.14.18.1) to browning potential (BP) was studied in buffer extracts of peach [Prunus persica L. Batsch) and nectarine [P. persica var. nectarine (L.) Batsch] fruit skin, The BP varied among cultivars with 'Flavorcrest' having the highest value and 'Maycrest' the lowest, On average, over 83% of the browning measured at the end of the 5-hour incubation occurred during the first hour, The total soluble phenolics (TSP), the total anthocyanin (TA), and glutathione content (GLU) varied among cultivars, but were not significantly correlated to the BP, Of the phenolics determined by HPLC, only chlorogenic acid had a significant positive correlation and epicatechin a significant negative correlation with BP by the first hour of incubation, The PPO activity, ranging from 4 to 11 optical density units per gram dry weight per minute among peaches and nectarines, was not significantly correlated with BP. However, no browning was detected if the buffer extract was previously boiled. These results indicated that browning in the buffer extracts of peach and nectarine skin tissue depends on the presence of PPO activity and chlorogenic acid, which are major contributors to enzymatic browning.