Abstract:This investigation aimed to compare the effects of ice crystals, endogenous proteases, and oxidation on the quality of obscure pufferfish (Takifugu obscurus) fillets during frozen storage, and detemine the dominant factors impacting their quality deterioration. The fillets were immersed in 1) liquid nitrogen, 2) iodoacetic acid solution, or 3) antioxidant mixtures (tea polyphenol and ascorbic acid solution), designed to inhibit the formation and growth of large ice crystals, activities of endogenous proteases, and the oxidization of proteins and lipids during storage, respectively. Therefore, the roles of these three factors in changing the quality of the frozen pufferfish fillets were differentiated. The hardness, thawing loss, cooking loss, total volatile basic nitrogen (TVB-N), K value, activity of Ca2+-ATPase, myofibril fragmentation index (MFI), and myofibril lengths were evaluated as quality indicators. The results showed that controlling the growth of ice crystals on the frozen pufferfish fillets had the greatest impacts on quality. After 24 weeks, the hardness of frozen pufferfish fillets with smaller ice crystals was about 26.8 % and 20.5 %, higher than that with the inhibition of endogenous proteolytic activities and oxidation, respectively. When it came to the thawing loss, it was about 44.2% and 44.8% lower with quick-freezing than in the other two groups. In addition, the TVB-N, K value, and activity of Ca2+- ATPase with the treatment of liquid nitrogen before freezing changed more slowly. In this group, the values of the quality indicators were 10.5 mg/100 g, 6.8 %, and 1.43 μmol Pi/mg/10 min after 24 weeks, respectively. As a result, ice crystals, endogenous proteases and oxidation have all contributed to the deterioration of frozen pufferfish fillets. Among them, the formation of ice crystals was the dominant factor for quality loss in frozen pufferfish fillets and the effects from the endogenous proteases and oxidation on the quality of pufferfish fillets followed, and there was no significant differences between these two factors.
