Relationship between Chemical Changes in 5'-Ribonucleotide Umami Seasonings and Their Behavior of Taste during Cooking

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The behavior of thermal degradation of 5'-ribonucleotide seasonings (IMP, GMP) and the interaction of them with other food components during cooking and food processing were investigated. The mechanism of thermal degradation of IMP and GMP was evaluated kinetically in aqueous solution as follows: The main reaction of the thermal degradation was the hysrolysis of the phosphoric ester bond in the nucleotides. The half-times At 10OﾟC were: IMP, 8.7 hr (pH 4.0), 13.1 hr (pH 7.0), 46.2 hr (pH 9.0); GMP, 6.4 hr (pH 4.0), 8.2 hr (pH 7.0), 38.5 hr (pH 9.0). The behavior of thermal degradation of IMP in commercially available umami seasoning extract was very similar to that of IMP in aqueous solution. When the umami seasoning powder was stored at 60ﾟC under different water activities (Aw, 0-0.8), IMP was remarkably degraded at Aw 0.8, suggesting that some interactions occurred between IMP and other components in the powder. The antioxidative ability of IMP and GMP at various Aw (0-0.75) was investigated, showing that IMP and GMP exhibited significantly the ability at Aw 0.5. The possible mechanism for the antioxidative ability of IMP and GMP was assumed to be their cheleting action.