Changes in free amino acid contents in juvenile mackerel Scomber japonicus muscle during ice storage.

Abstract

Changes in the contents of free amino acids (FAA) in white and dark muscles of juvenile mackerel scomber japonicus were investigated during ice storage. The alterations of creatine, trimethylamine oxide (TMAO), and volatile base-nitrogen (VB-N) levels were also examined. In white muscle during storage for over 40 days, VB-N rapidly increased in level after about 20 days, indicating the onset of microbial spoilage; no measurable increase was observed in the dark muscle during the entire storage period (8 days). The fresh white muscle contained a large quantity of free histidine (510mg/100g), while a remarkably high concentration of taurine (950mg/100g) was present in the fresh dark muscle. Most FAA, except histidine and taurine, increased in level to certain extents throughout all storage periods. Creatine was present in a higher concentration in the white than in the dark muscle (590 vs. 200mg/100g) but its level remained unchanged in either muscle during the whole storage periods. TMAO existed in a higher concentration in the dark than in the white muscle (77vs. 12mg/100g). The level in the former tissue decreased slightly by 2 day after the beginning of storage but that in the latter showed little change during the entire storage period. The increase in the FAA contents during storage was discussed in relation to autolytic chracteristics and microbial spolage of the muscle tissues of juvenile mackerel.