Studies on non-volatile amines as potential indexes for freshness of marine invertebrates

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The concentrations of non-volatile amines were investigated in relation to decomposition processes of common squid, scallop and prawn. Putrescine (Put), agmatine (Agm), cadaverine, tyramine and tryptamine were well separated from each other by gradient elution high performance liquid chromatograph with a fluorescence detector. Agm appeared to be most useful as a potential index for freshness of common squid. Agm was detected in small amounts in the fresh muscle and the concentration increased with storage time, exceeding 30 mg/100g at the stage of initial decomposition and reached the level of 40 mg/100g at the stage of advanced decomposition. Put was not produced at the acceptable stage and detected in small amounts (less than 1 mg/100g) at the stage of initial decomposition. Therefore, Put was useful as an indicator for the stage of initial decomposition. In scallop Put was detected at the level of 0.5 to 0.7 mg/100g at the stage of initial decomposition and exceeded 2.1 mg/100g at the stage of advanced decomposition. Put appeared to be useful as a potential indicator for freshness of scallop adductor muscle. In prawn Put was also suitable as an index for decomposition. Put was not present in the fresh muscle, detected in small amounts (less than 1 mg/100g) at the stage of initial decomposition and increased remarkably as decomposition progressed. VBN and K value showed 30 mg/100g and 30 %, respectively, at the stage of initial decomposition. The changes in non-volatile amines contents and viable counts of total bacteria were examined in the meats of squid and scallop with and without chloramphenicol. It was elucidated that non-volatile amines were not produced from amino acids by decarboxylases of muscle but by those of bacteria. When viable counts reached the level of 10^3/g in squid and 10^3/g to 10^4/g in scallop, the formation of non-volatile amines was observed.