Change of K-value and water state of yellowfin tuna Thunnus albacares meat stored in a wide temperature range (20°C to -84°C)

The study on K value change at low temperature storage had been carried out down to a temperature of -40 degreesC, however, there was no evidence about this reaction rate if the temperature were lowered below the storage temperature normally used especially for tuna meat (-60 degreesC). The rate of K value change (k(f)) of yellowfin tuna (Thunnus albacares) meat was determined during storage at a wide temperature range (20 degreesC to -84 degreesC). The logarithm of K'(= 100 - K value) was used in this study and its plot against storage time yielded a straight line, which indicated an apparent first-order reaction for all temperature storage. Furthermore, physicochemical characterization of water in tuna muscle was carried out using Differential Scanning Calorimetry (DSC) at very low temperature. The temperature dependence of this reaction was analyzed by an Arrhenius's plot that resulted in two break points. The first break point occurring at freezing point might be due to the freeze effect. The second break point was at -10 degreesC. The reaction rate change steeply declined at the temperature range of -70 degreesC to -84 degreesC, and was thought to be related to glass transition which may occur in the fish sample.