Dual effect of β-cyclodextrin (β-CD) on the inhibition of apple polyphenol oxidase by 4-hexylresorcinol (HR) and methyl jasmonate (MJ)

Inhibition of red delicious apple polyphenol oxidase (PPO) by three non-related antibrowning agents has been studied at different substrate concentrations. The main apple polyphenol, cholorogenic acid (CA), has been used as a substrate. The three agents (beta-cyclodextrin [beta-CD], 4-hexylresorcinol [HR] and methyl jasmonate [MJ]) showed an inhibitory effect at every substrate concentration tested. From the inhibition constant (K-i) values, it was concluded that the inhibitors' strength decreased in the order HR > beta-CD > MJ. A combination of beta-CD-HR had a synergic effect, which was not observed for the combination of beta-CD-MJ. A competitive-type inhibition was obtained for HR with a K-i = 0.26 mM. beta-CD and MJ behaved as mixed-type inhibitors, although more than one inhibitory mechanism is discussed for both agents. (c) 2006 Elsevier Ltd. All rights reserved.