The nature of β-cyclodextrin inhibition of potato polyphenol oxidase-catalyzed reactions.

There is general interest in strategies to control polyphenol oxidase (PPO)-initiated enzymatic browning because it is often associated with declining food quality. Cyclodextrins are cyclic glucan oligosaccharides that form inclusion complexes with a number of PPO substrates. This study focuses on the effect of β-cyclodextrins (βCyD) on PPO-catalyzed reactions. Potato enzyme extracts and semi-purified potato PPO served as enzyme sources. Substrates included phenolics endogenous to potatoes. Reaction time-courses were followed spectrophotometrically; rates were compared by analysis of variance. Extents of βCyD inhibition of PPO-catalyzed reactions are shown to be substrate specific and can be quantitatively accounted for based on degrees of βCyD substrate sequestration. There was no evidence for direct irreversible βCyD inactivation of potato PPO. An apparent "direct PPO inactivation" by βCyD is shown to result from a sequence of sequestration-dependent reactions that occur in commonly employed assay systems for the quantification of PPO in fruits and vegetables.