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The effects of β-cyclodextrin (β-CD) on polyphenol oxidation catalyzed by apple polyphenol oxidase (PPO), endive PPO, or mushroom tyrosinase have been compared. β-CD forms a complex with phenolic substrates of PPO by inclusion. Assuming a 1:1 β-CD/phenol stoichiometry, and assuming that PPO is inactive on the complex β-CD/phenol, K D values were similar when determined kinetically by inhibition of apple PPO or endive PPO. However, the experimental velocities found during inhibition of mushroom tyrosinase by β-CD were higher than the values predicted by this model. In this latter case, it was assumed that mushroom tyrosinase is able to act on the complex β-CD/phenol. A new model based on this assumption allows experimental and calculated velocities to be fit in presence of β-CD. Keywords: Enzymatic browning; polyphenol oxidase; apple; endive; mushroom; inhibition; cyclodextrin

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Peroxidases (POD) of crude extracts from barley and wheat germ were separated, partially purified using salt fractionation, ion-exchange and hydrophobic interaction chromatographies and their properties examined. Barley and wheat germ POD contained basic, neutral and anionic isoforms as confirmed by isoelectric focusing. Toyopearl-Bug1 650 M chromatography resolved POD into four cationic fractions. Chromatography of wheat germ extract on CM-Sepharose isolated an anionic and a neutral @action. Following chromatography on Concanavalin-A Sepharose, enzymes from both cereals showed diferences in their elution properties. Optimum pH ranges were 4.0 to 5.5 (barley) and 5.3 to > 6.3 (wheat germ) and POD reacted differently under acidic or basic conditions. Their catalytic behavior in the presence of calcium also differed. Kinetics of POD were of Michaelian type with a ping-pong mechanism and Michaelis constants of guaiacol oxidation in the presence of hydrogen peroxide variedfrom one enzymatic group to another.