Abstract
A studY was conducted on the effect of melanoidin, a brown and polymeric pigment which is finally accumulated in the Maillard reaction, on the activity of α-amylase from human salive. Melanoidin was prepared by the reaction between D-glucose and glycine. Soluble starch and maltotetraose were used as substrates for digestian. The enzymatic reaction medium was 0.02M sodium phosphate buffer (pH6.0) containing 1mM CaCl2. The reaction solution was incubated at 37°C. Oligosaccharides produced on digestion were determined by high-performance liquid chromatography. Melanoidin was found to exert an adverse effect on the activity of α-amylase. The effect of melanoidin on the enzyme was attributed to non-competitive inhibition on the basis of Lineweaver-Burk and Dixon plots. The Michaelis constant (Km) and inhibition constant (K1) were 3.3mM and 0.1-1.5%, respectively. The following factors were suggested to be involved in the inhibitory effect of melanoidin: (1) Interaction between the enzyme molecule and melanoidin. (2) Interaction between the substrate and melanoidin. (3) Interaction between Ca ions and melanoidin. Melanoidin was also found to constrain the thermalinstability of α-amylase.
