Thiol-Cyclodextrin: A New Agent For Controlling The Catalytic Activity Of Polyphenol Oxidase From Red Delicious Apple

Abstract

Polyphenol oxidase (PPO, EC 1.14.18.1) is the main enzyme responsible for enzymatic browning, a natural process which produces deterioration of fruits and vegetables. One alternative to prevent this undesirable process is to inhibit the catalytic activity of PPO by encapsulating enzyme’s substrates in cyclodextrins (CD). In this article the effect of a Thiol-CD on PPO from Red Delicious apple was studied, demonstrating that this compound is a powerful tool for controlling oxidative processes in food. Thiol-CD could encapsulate the polyphenols, natural substrates of the enzyme, by means of the cyclodextrin hydrophobic internal cavity. Simultaneously, through the thiol group, it could inactivate the PPO by reducing the copper ions from the active site of the enzyme. Moreover, thiol moieties could decrease the browning by reducing the quinones generated by oxidative processes. The isolation and purification of PPO from apple was performed in order to study those effects, different polyphenols, chlorogenic acid (CA) and 4-methylcatechol (4-MC), were assayed as enzymatic substrates. Both β -CD and Thiol-CD exhibited better enzyme inhibition value for CA than for 4-MC. Moreover, Thiol-CD showed an extraordinary performance compared with β-CD. When CA 10 mM was used, 5 mM β-CD gave 11 % PPO inhibition, meanwhile nearly 100 times less concentration of Thiol-CD (45 μM) gave 100 % of enzyme inhibition.