Maillard reaction products inhibit apple polyphenoloxidase

The effects of Maillard reaction products (MRP) on apple polyphenol oxidase (PPO) were evaluated spectrophotometrically at 400 nm after oxidation of 4-methylcatechol. MRP, synthesized under different conditions including heating time, type of amino acids, pH and concentration of both amino acid and glucose, showed different effects on apple PPO. The inhibitory effects of MRP. heated for 7 h at 90 °C and synthesized from various amino acids with glucose, were as follows: arginine = histidine > ysteine > lysine. The MRP synthesized from glutamic acid or valine enhanced rather than inhibited PPO activity. Increasing the heating time of histidine-glucose solutions also enhanced the inhibitory effect. However, a slight decrease in the inhibitory effect was observed in the cysteine-glucose solutions after 3 h of heating. The MRP synthesized at low pH levels was a more effective inhibitor than the MRP synthesized at higher pH levels.