Abstract
A method to differentiate between frozen-thawed and unfrozen fillets of yellowtail Seriola quinqueradiata was investigated by a combination of Torrymether readings (TMR) and K values (KV). Fresh fillets before storage and fillets held in ice for about a day showed an average TMR of approximately 11. KV for corresponding fillets were less than 1 and about 6%, respectively. TMR for frozen fillets stored at -20°C for about a day prior to thaw and unfrozen fillets held in ice for 18 days were both 0. The frozen-thawed fillets had relatively low KV, while the unfrozen ones had a considerably high level (approximately 3 vs. 50%), suggesting that the former fillets can be differentiated from the latter by measuring the TMR and KV. Thawed fillets previously frozen only in liquid nitrogen and those frozen by this and subsequently stored at -20°C for about a day also showed a TMR of 0. TMR of frozen-thawed fillets measured on the bone as well as on the skin side were much lower than those of the unfrozen fillets. A possibility to dif-ferentiate frozen (-20°C for a day)-thawed from unfrozen fillets by a combination of visual ob-servation of the skin color and the TMR or KV measurement was also indicated.
