ABSTRACTMixing strawberries ground under liquid nitrogen with polyvinylpyrrolidone alone or combined with Amberlite XAD‐4 in pH 4.5 buffer yielded stable polyphenoloxidase (PPO) extracts. Temperature stability of the enzyme varied with substrate and followed first order kinetics of inactivation. pH optima were 5.5 with catchol and 4.5 with 4‐methylcatechol. Maximum activity was with D‐catechin, followed by 4‐methylcatechol and pyrogallol with no cresolase activity. Inhibition occurred with diethyldithiocarbamate, potassium metabisulfite, KCN and dithiothreitol. Benzenesulfinic acid, cysteine and ascorbic acid blocked the browning reaction without enzyme inhibition. Extraction with Dowex AG 2‐X8 resulted in browning. No loss in activity after 95 days occurred with quick‐frozen fruit stored under nitrog
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