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

研究了5′-核糖核苷酸调味料（IMP、GMP）在烹饪和加工过程中的热降解行为及其与其他食品成分的相互作用。对IMP和GMP在水溶液中的热降解机理进行了动力学评价：热降解的主要反应是核苷酸中磷酸酯键的水解。在10℃时的半周期分别为：IMP， 8.7小时（pH 4.0）， 13.1小时（pH 7.0）， 46.2小时（pH 9.0）；GMP， 6.4小时（pH 4.0）， 8.2小时（pH 7.0）， 38.5小时（pH 9.0）。IMP在市售鲜味调味膏中的热降解行为与IMP在水溶液中的热降解行为非常相似。不同水活度（Aw, 0 ~ 0.8）下，保鲜粉在60℃的温度下，IMP在Aw 0.8下被显著降解，表明IMP与鲜味粉中的其他组分发生了相互作用。研究了IMP和GMP在不同Aw值（0-0.75）下的抗氧化能力，发现IMP和GMP在Aw值0.5时表现出显著的抗氧化能力。IMP和GMP的抗氧化能力可能与它们的剪切作用有关。

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.