Density functional computational studies on ribose and glycine Maillard reaction: Formation of the Amadori rearrangement products in aqueous solution

By following the Hodge-scheme, and considering the formation of the Amadori rearrangement products (ARPs) as one of the possible intermediates in the early stage, density functional theory calculations have been performed at the standard state on the proposed mechanisms of the Maillard reaction of cyclic ribose (c-Rib)/open-chain ribose (Rib) and glycine species under different pH conditions in aqueous solution. The result reveals that both c-Rib and Rib can participate in the reaction. Rib has been found as more reactive than c-Rib in the reaction. The reactions under basic and neutral conditions are supposed to be the most and second most favourable for the formation of ARPs. Production of both of the enol and keto forms of ARP have been found as feasible under basic condition, whereas the neutral condition is only favourable for producing the enol form of ARP. Therefore, the rate of browning under basic condition is assumed higher than that of the neutral condition. Formation of all intermediates in the proposed mechanisms has been found as unfeasible in the reaction under acidic condition and at the isoelectric point of glycine. Therefore, production of ARPs under these conditions is assumed to be stalled under these conditions, resulting into lower browning rate. Formation of Rib through the cleavage of glucose has been assumed less feasible than the formation of glucose from Rib and formaldehyde in aqueous solution.