Changes of some quality parameters in rainbow trout (Oncorhynchus mykiss) during chilled and frozen storage

To examine changes of some quality parameters in rainbow trout during chilled and frozen storage, 60 subjects were slaughtered the same day and maintained at a)18 degrees C, b)4 degrees C, c)4 degrees C in ice, d)-20 degrees C, and e)-80 degrees C. Conductivity measurements on whole fish, water-holding capacity (WHC) of muscle by compression method, pH and K1 obtained using a biosensor system on muscle juice were determined at slaughter and during following days; malonaldehyde in muscle of deep-frozen fish was quantified using the TBA method. The d) and e) samples in particular consisted of 30 days of freezing and 90 days of deep-freezing +4d after thawing at 4 degrees C, respectively. Conductivity scores decreased at different rates during 18 degrees C and chilled storage and was not useful for frozen fish. WHC decreased markedly within the first day at 18 degrees C while at 4 degrees C remained good two days from slaughter. In subjects stored with c), d) and e) the worst WHC was shown at the first days, particularly in deep-frozen fish. The K1 indicated still acceptable values in fish for a)a few hours, b) and d) two days, c) and e) three days after thawing. A combination of K1 % and conductivity scores can be useful for quality evaluation of fish maintained with different storage systems.