Study On The Quality Changes During Metapenaeus Ensis Freezing Storage

Metapenaeus ensis is great source of high-quality protein,low in fat and rich in omega-3 fatty acids,it has become the most-favored seafood product.While,fresh shrimp is highly perishable after capture,lead to quality deterioration which is associated with microbial spoilage,chemical changes and melanosis(blackening).Thus,many methods are used to retard the quality loss during shrimp storage and freezing is most common and more easily available.While,although freezing is the best way to inhibit microbial growth and slow chemical changes,it is reported that freezing shrimp also suffered quality deterioration due to oxidative,enzymatic and microbial spoilage continue at slower rate.Recently,many studies focused on the storage method and fresh-keeping agent of shrimp.While,the mechanism of quality changes for freezing shrimp was very rare,especially for Metapenaeus ensis.The aim of this study is to clarify the quality changes and its mechanism during shrimp freezing storage.In this thesis,the quality changes(pH,TVB-N,texture,flavor compounds and nucleotides)were measured after freezing 0,1,3,5 and 7 weeks respectively.Then,the mechanism of the quality changes was studied through analyzing protein characteristics(total protein SDS-PAGE,UV absorption spectrum,solubility and the size of the myofibril),lipid oxidation,fatty acid compounds and microstructure.The results were as following:The pH value and TVB-N of the Metapenaeus ensis increased during the freezing storage.The texture,flavor and taste were getting worse.The research on mechanism of the shrimp quality changes showed that:(1)The protein molecule became degraded and polymerizated which indicated that the proteins were oxidized and denatured.(2)The TBARS value and the proportion of SFA increased,and the PUFA decreased.It showed that the lipid oxidation may happen in muscle.(3)The observation of the microstructure showed the gaps between tissues became larger during shrimp frozen storage which give clues that the formation of ice crystals could result in mechanical damaged to the shrimp muscle.