Mechanism for the inhibition of apple juice enzymatic browning by Palo Fierro (desert ironweed) honey extract and other natural compounds

Inhibition of Red Delicious apple juice browning and apple polyphenoloxidase (PPO) activity by four natural anti-browning agents [palo fierro honey extract (PFH), caffeic acid phenethyl ester (CAPE), l-cysteine (Cys), and 4-hexylresorcinol (4HR)] has been studied. Browning of apple juice was markedly reduced by 4HR, Cys, and PFH, however, little effect was observed with CAPE. PFH, CAPE, and 4HR showed high inhibition of apple juice PPO. When the inhibition mechanism of these compounds over partially purified apple PPO was studied using chlorogenic acid as substrate, PFH acted as a noncompetitive inhibitor of apple PPO, with Ki = αK = 0.8 g/L, and IC50 ranging 1.1–1.7 g/L. Cys showed an inhibitory pattern which could not be fitted to any type of reversible inhibition (IC50 0.02–0.03 g/L), while CAPE showed low inhibitory activity, which could be due to co-precipitation processes. PFH could be considered as an effective natural compound to reduce apple juice browning.