2018 年 29 巻 1 号 p. 35-43
Two different storage conditions of short-neck clams ［1） Immersion in 3% NaCl solution; 2） air exposure］ were evaluated for the chemical changes and the freshness during storage at 4℃ for 7 days. The weight of the clams exposed to air significantly decreased during the storage period. The shells were closed or presented a response to stimulus after storage for 3 days in both conditions. The total viable count in the clams exposed to air increased rapidly after 5 days. An odor-based sensory evaluation revealed that after storage for 7 days in both conditions, about half of the clams underwent initial decomposition. After 7 days of storage, the percentage of clams that showed no response was 60% in the saline-immersed group, and 10% in the air exposure group.
The effect of cooking on shell-opening during the storage of short-neck clams was also investigated. For cooked clams stored in the NaCl solution, all shells opened completely after storage for 3 days, and 33% of the clam shells opened completely after 7 days of storage. For cooked clams exposed to air, all shells opened completely after storage for 2 days, and 93% of the clam shells opened completely after 7 days of storage.
Compounds such as free amino acids, ATP and related compounds, succinic acid, and lactic acid were extracted from the soft parts of clams and analyzed. Compared with that at day 0, the total amino acid content increased by 20-23% after storage for 2 days. The content of extracted compounds rapidly decreased after 7 days in clams stored in the NaCl solution. The K’ values, which were calculated from the levels of ATP and related compounds, showed a rapid increase of 17% after storage for 5 days. The increase patterns of K’ values and lactic acid contents were consistent.