Changes in Contents of Free Amino Acids, Trimethylamine, and Nonprotein Nitrogen of Oyster during Ice Storage

Abstract

The contents of free amino acids (FAA) in the whole body and adductor muscle of oyster Crassostrea gigas, which had been stored in ice until they reached early stage of spoilage, were measured. Trimethylamine (TMA), and nonprotein nitrogen (NP-N) together with volatile base nitrogen (VB-N) and trimethylamine oxide (TMAO), were also determined. The content of VB-N at 0day was relatively low (10.5 and 8.7mg /100g) and increased significantly thereafter in both the whole body and adductor muscle during storage for 2weeks. Only a little TMAO was detected and TMA was about 5 mg/100g; there was almost no change in the contents during storage in either the whole body or adductor muscle. NP-N was 485mg/100g in the whole body and 515mg/100g in the adductor muscle at 0day, and no measurahle change thereafter. In fresh whole body, the level of taurine was extremely high (974mg/100mg) and the amounts of glycine, proline, glutamic acid, and alanine were relatively large. Taurine and glycine changed little throughout the storage period. Alanine showed a slight increase, while proline and glutamic acid decreased. In fresh adductor muscle, the level of taurine was also high (768mg/100g) and the levels of glycine, β-alanine, arginine, alanine, and proline were relatively high. Taurine and glycine exhibited little change during storage. Remarkable increase in alanine and decrease in glutamic acid levels were observed.