IMP and GMPwere degraded during storage in the presence of methyl linoleate (ML), this degradation being caused by the peroxidation of ML.The mechanisms for degradation in the first period (0-7 days) and in the second period (8-15 days) of storage were different. The primary products (hydroperoxides) ofperoxidized MLcontributed to the degradation in the first period, and the secondary products (carbonyl compounds) contributed in the second period. Especially, IMP reacted with the secondary products to form its base (hypoxanthine) by cleavage of the N-C bond. This thermal degradation was depressed in the presence of divalent metal ions.2) We also observed that other food components in a water extract (soup) from commercial seasoning powder (Dashinomoto) scarcely influenced the thermal stability of 5/-ribonucleotides.3) However, the interaction between 5'-ribonucleotides and each food component has not been investigated in detail. In a food system where food componentsareTo whomcorrespondence should be addressed.

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