| Tilapia is a globally important species in aquaculture because of its rapid growth rate,firm and flavorsome flesh,and nutritious.Currently,chilled is the main preservation method during long-distance storage and transportation in China.However,wide temperature fluctuation in fresh medium and short cold-keeping time may lead to negative impact on freshness of aquatic food.Therefore,this study is aim to investigate the alternative met hods that could enhance the quality and freshness of tilapia.Firstly,the partial freezing ice formula of partial-frozen for aquatic products,such as sodium polyacrylate,sodium chloride and propanediol,were optimized on the basis of single factor experiments at the point of-3~-1.5 ?.Box-Behnken experimental design and response surface methodology(RSM)were used to find the optimal formula.The results showed that the optimal partial freezing ice formula was 1.0% sodium polyacrylate,0.6% sodium chloride and 2.1% propanediol,which can keep the temperature of partial-frozen(-3~-1.5 ?)of aquatic for 130 min.Compared with traditional partial freezing ice of sodium chloride,complex partial freezing ice can prolong for about 60 min.Therefore,partial freezing ice formula could keep longer low-temperature time,make the temperature more stable and be helpful for the storage and processing of aquatic products.Secondly,the Nile Tilapia was studied experimentally based on low-temperature preservation for aquatic products,which helps to solve preservation problems of fishery products.Due to its high-quality proteins,strong reproductivity,fast growth,strong tolerance to complex environmental conditions,and strong immunity,Nile Tilapia had become the most frequently seen alien fish in China,especially South China in recent years.The Nile Tilapia used in this study was pre-chilled at 2? or 10? or room temperature before sliced,fillets were stored in partial freezing ice until the ice completely melted in 48 hours.We evaluated the effects of different pre-chilling temperatures on the fillet freshness and quality by monitoring temperature of the ice and the fillet as well as measuring fillets' rigor index,TVB-N,pH,K value,and TBA.The results showed: At room temperature(20 ?),partial freezing ice for aquatic products heats up slowly within 36 hours and is good for retaining freshness of the fillets.The fillets prechilled at 10 ? reached the maximum rigidity in 5 hours.Compared with the other two groups,it took nearly 3 more hours.The increasing range of TVB-N?pH?K value of fillets pre-chilled at 10? is also slightly lower than the other group.In view of the above results,10 ? is the best pre-chilling temperature,and this temperature will be more conducive to the fillets' freshness,subsequent processing and storage.Thirdly,to study the effect of tilapia fillets quality during partial freezing ice storage and find its freezing point,this research compared their sensory evaluation,pH,drip loss rate,whiteness,total viable counts,texture,solubility of myofibrillar protein and contents of total sulfhydryl under different temperatures.The results indicated that tilapia fillets freeze at-0.8?,and partially freeze at-2.5±0.3?.The content,TVB-N and total viable counts of tilapia fillets stored by partial-freezing were lower than those stored by traditional ice after 18 days,33% and 26% respectively.The observartion of muscle tissue structure showed ice crystals in tissues during partial-freezing storage damaged myofibers,and drip loss rate and whiteness were also higher than the control group.In all,partial-freezing was necessary to improve the quality of stored tilapia fillets,which can prolong their expiration to 18 days.Fourthly,the content of salt-soluble protein,actomyosin surface hydrophobicity,Ca2+-ATPase activity,mercapto and SDS-PAGE in low(-4 ?)temperature and ice stored Nile Tilapia fillets was measured in this study,to find out the influence of low temperature and ice stored on fillets' protein biochemistry,borneol and the related mechanism.The content of salt-soluble protein,Ca2+-ATPase activity and actomyosin mercapto both decreased in the partial freezing group and the control group as time went by,but the partial freezing group decreased in a lower speed than control group.The content of salt-soluble protein and Ca2+-ATPase activity decreased severely in the early period(0-9days)during the storage,and decreased slightly afterwards.Actomyosin surface hydrophobicity increased as the storage time extended.Hydrophobic residues exposure during the period of storage led to protein structure change in the fillets,and the increasing speed of the hydrophobicity in the partial freezing group was slower than that of the control group.After the SDS-PAGE analysis on the fillets,we found that both myosin heavy chain and actin degraded.Light density of electrophoresis strip in the partial freezing group was bigger than that of the control group at the same time,but the protein degradation of the partial freezing group was lower. |
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