Abstract: This study was an attempt to examine the viability of pre-cooling before freezing of tilapia fillets. Fresh tilapia fillets were soaked in ice water prior to frozen storage at different temperatures, which served as a treatment group, and those directly frozen were used as a control group. The pH, color, drip loss after thawing, total volatile base nitrogen (TVB-N) and texture parameters of the fillets were measured at regular intervals during frozen storage to evaluate the effect of pre-cooling on the quality of frozen fish fillets. The results showed that the pH of fish fillets frozen at ?7 ℃ was more influenced by pre-cooking than at other freezing temperatures, and it decreased from day 10 to 20 of storage at ?7 ℃ but began to increase again at other freezing temperatures. Both color L* and a* values decreased continuously during the storage process, and the decrease was smaller at lower storage temperature. These color parameters were increased by pre-cooling as compared to control. In addition, post-thaw exudative moisture loss was higher at lower freezing temperature, reaching its maximum value on day 30 of storage, 7.47% and 6.82% at ?18 and ?7 ℃, respectively. The TVB-N value of frozen fish fillets at ?4 and ?7 ℃ was more significantly affected by pre-cooling during the first 20 days of storage, but no significant difference was observed later. There was a big difference between the TVB-N values with and without pre-cooling on day 30 of storage ?18 ℃, which were 8.04 and 9.87 mg/100 g, respectively. An increased difference in chewiness between the treatment and control groups was observed during the first 20 days of frozen storage at lower temperature, which tended later to be consistent. No significant difference in hardness was noted at the same temperatures but there was a significant difference in elasticity between the two groups at ?4 ℃ (P > 0.05), but not at other temperatures (P < 0.05). However, cohesiveness was changed irregularly. In conclusion, pre-cooling treatment can improve some quality attributes of frozen talipia fillets, thereby maintaining their quality.

Key words: frozen tilapia fillets, pre-cooling, rigor mortis, texture, quality