MAILLARD REACTION-PRODUCTS INHIBIT APPLE POLYPHENOLOXIDASE

The effects of Maillard reaction products (MRP) on apple polyphenol ox idase (PPO) were evaluated spectrophotometrically at 400 nm after oxid ation 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. Th e inhibitory effects of MRP, heated for 7 h at 90 degrees C and synthe sized from various amino acids with glucose, were as follows: arginine = histidine > cysteine > lysine. The MRP synthesized from glutamic ac id or valine enhanced rather than inhibited PPO activity. Increasing t he heating time of histidine-glucose solutions also enhanced the inhib itory effect. However, a slight decrease in the inhibitory effect was observed in the cysteine-glucose solutions after 3 h of heating. The M RP synthesized at low pH levels was a more effective inhibitor than th e MRP synthesized at higher pH levels.