Inhibition kinetics of oligochitosan as an uncompetitive inhibitor on fuji apple polyphenol oxidase

This study aimed to investigate the effect of oligochitosan on purified polyphenol oxidase (PPO) from Fuji apple and the associated mechanisms. PPO was firstly separated and purified in a four-step procedure and the molecular weight was estimated to be about 65 kDa by SDS-PAGE. PPO showed an optimum activity at pH 7 and 35 degrees C, and it was stable in the temperature range of 25-55 degrees C with more than 50% residual activity. Thermal inactivation parameters indicated that the Fuji apple PPO was very heat-labile. Using catechol as the substrate, the PPO activity decreased with the increase of oligochitosan concentration, and only 30% activity remained when the concentration reached 4mg/mL. Oligochitosan showed uncompetitive type reversible inhibition with K-i value of 0.26mg/mL. Data obtained in this study provided theoretical basis for controlling enzymatic browning during apple processing with oligochitosan. Processing operations, such as peeling, cutting, and juicing have the same problem: enzymatic browning, which causes a decrease in market value and economic loss. The most common approach for preventing browning is using anti-browning agents, however, consumers are demanding a reduction in the overall use of chemicals on foods safe and asking effective substitutes especially natural inhibitors with the increased health awareness. This research systematically characterizes the enzymatic browning related PPO from apple and demonstrated that oligochitosan can inhibited PPO activity as an uncompetitive inhibitor, which will help in the development of oligochitosan to be a new type of anti-browning agent.