Abstract: This study focused on the effect of initial pH in a fructose-lysine model system on the properties of Maillard reaction products (MRPs) related to the inhibitory effect on banana enzymatic browning. MRPs were prepared through the reaction of 0.5 mol/L fructose and 0.5 mol/L lysine at a pH ranging from 2 to 11, 110 ℃ for 1 h. Then, their antioxidant activity (including DPPH free radical scavenging ability and reducing power), chelating copper activity and the inhibitory effect on polyphenoloxidase banana were evaluated. The results showed that the Maillard reaction between fructose and lysine could be accelerated at alkaline conditions, however, MRPs prepared from acidic conditions (especially at pH 2 or 3), were more effective in inhibiting banana polyphenoloxidase and scavenging DPPH free radicals. The reducing power of MRPs prepared at pH 9 was highest, while those prepared at pH 2 had the lowest reducing power. Chelating copper activity of MRPs prepared at pH 2—4 or pH 11 was predominant. Generally , initial pH showed a significant effect on the efficacy of MRPs for inhibiting banana enzymatic browning, and the properties related to the inhibitory effect of MRPs prepared at different initial pHs were much different from each other, such as DPPH radical scavenging ability, reducing power, chelating copper activity and the inhibitory effect on banana polyphenoloxidase. It could also be deduced that early stage MRPs may play key roles in inhibiting banana polyphenoloxidase.

Key words: Maillard reaction products (MRPs), initial pH, banana, polyphenoloxidase, enzymatic browning