Reversible inhibition of polyphenol oxidase from apple using L-cysteine

Alternate strategies for prevention of enzymatic browning of fruits and vegetables are required by food industries due to restrictions and several negative health attributes of sulphites, which are effective inhibitors of enzymatic browning reaction. These reactions result mostly from polyphenol oxidase (PPO). The present study was conducted to evaluate the antioxidant and PPO inhibitory potential of L-cysteine. Studies have revealed that with increase in concentration of L-cysteine there was corresponding decrease in the rate of browning reaction and the activity of PPO. The kinetic study indicates that PPO inhibition by L-cysteine is non-competitive. The results suggest that the L-cysteine is a time bound inhibitor of PPO, since its highest concentration (5 mM) gives protection up to 4 h having no further effect on the rate of browning reaction in apple juice. The assessment of radical-scavenging ability of L-cysteine demonstrated that it has high affinity towards a stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH).