Quality And Protein Properties Changes In Chilled Nile Tilapia(Oreochromis Niloticus) Fillets Previously Sterilized By Ozonised Water Treatment And Inhibition Of Protein Degradation

Nile tilapia（Oreochromis niloticus） is one of the widely cultured fish species in the world, and has been known as a good raw material in seafood processing field. To extend their shelf-life, tilapia fillets are generally sterilized during processing. Ozone（O3） is a powerful, broad-spectrum antimicrobial agent, which has attracted increasing attention as a substitute for chlorine for inactivation of spoilage and pathogenic microorganisms in aquatic products processing. Because it is an environmentally friendly technology, the ozonised water sterilization treatment is accepted by tilapia processing enterprises and consumers. However, reactive oxygen species（ROS） can be produced in the ozonised water sterilization step, which may accelerate denaturation of tilapia protein and lipid oxidation. These changes may lead to adverse effects on aquatic product.In view of above reasons, this present study was designed to investigate storage life and quality of Nile tilapia fillets sterilized by ozonised water treatment during storage in ice, by evaluating sensory, physical, chemical, and microbiological changes. Changes in biochemical properties of muscle protein from Nile Tilapia fillets sterilized by ozonised water treatment during ice storage were investigated from the aspect of the denaturation of protein. Inhibition of protein oxidative degradation of tilapia fish was studied by adding EGCG in fish muscle. The SDS-PAGE and MS-MS technologies were applied to investigate the changes in protein and researched the protein indicators. The results were as follows:1. Quality changes in commercial-sized Nile tilapia fillets sterilized by 4.0 mg/L ozonised water for 30-min and stored in ice for 18 days were evaluated. Malondialdehyde content increased 26.0% after treatment at day 18, while drip loss rate, lightness, chroma, whiteness index and whilst hue values in the treated group were significantly higher. These changes indicated that treatment had some adverse effects on fillet quality. Total volatile basic nitrogen decreased 17.6% when compared to the control at day 18. Hardness and chewiness improved 10.4% and 9.3% by the treatment at day 0. Besides, pH showed no significant differences between both groups throughout the storage period（except day 12）. Based on microbiological analysis and sensory evaluation, the shelf-life of treated and control fillets was 14 and 11 days, respectively. The results of this study indicate that ozonised water treatment is effective in reducing total viable counts and extending shelf-life during ice storage.2. In this paper, the changes in biochemical properties of muscle protein from Nile Tilapia fillets sterilized by ozonised water treatment during ice storage were investigated by changes evaluation of myofibrilla protein salt solubility, Ca²⁺-ATPase activity, surface hydrophobicity of actomyosin, total sulfhydryl content of actomyosin and carbonyl content. The results showed that different degrees of protein degeneration of treated and control group Nile Tilapia fillets were all occurred during ice storage. The myofibrilla protein salt solubility, Ca²⁺-ATPase activity and total sulfhydryl content all decreased as the storage time was extended. Moreover, both surface hydrophobicity of actomyosin and carbonyl content increased during ice storage. After being stored for 20 days, the myofibrilla protein salt solubility, Ca²⁺-ATPase activity and total sulfhydryl content of treated group group decreased by 76.6%, 89.8% and 66.7% respectively, while those of control group declined by 69.1%, 86.5% and 62.3%. On the other hand, surface hydrophobicity of actomyosin and carbonyl content of treated group group increased by 111.8% and 76.5% respectively, while those of control group rose by 104.8% and 58.2%. At the same storage time, the myofibrilla protein salt solubility, Ca²⁺-ATPase activity and total sulfhydryl content of treated group group were lower than those of control group, and both surface hydrophobicity of actomyosin and carbonyl content were higher than those of control group. The research results indicated that the protein denaturation was promoted by the oxidation of ozonised water and ROS generated from ozonised water during storage period.3. The quality fraction of 0.0025%, 0.01%, 0.02% and 0.03% of EGCG had protective effect on protecting the myofibrillar protein of Nile Tilapia fillets. Among them, the best concentration was 0.01%. Six differently expressed protein were obtained in SDS-PAGE and MS-MS technologies. They were phosphatidylinositol 4-phosphate 3-kinase C2 domain-containing subunit alpha, BTB/POZ domain-containing protein KCTD16, unconventional myosin-VIIa-like, major histocompatibility complex class I-related gene protein-like, leucine-rich repeat-containing protein 16B-like isoform X4 and coiled-coil domain-containing protein 22-like isoform X2...