| Chinese shrimp,a kind of aquatic product widely distributed in China,because of its eminent nutritional and delicious taste,it is deeply loved by the public at home and abroad.However,due to high protein and moisture content,it is easy to rot and deteriorate due to microorganisms,endogenous enzymes and chemical action after fishing,which restricted the development of Chinese shrimp storage and transportation,processing industry.Although the traditional storage method of Chinese shrimp is easy to implement and low cost,it will cause the loss of nutrition and flavor of Chinese shrimp,and affect the edible value.Therefore,it is demand to evolution a fresh type of preservation technology to solve this challenge,so as to prolong its shelf life,and satisfy the needs of consumers and processing companies for Chinese shrimps.At present,freezing technology,as the third generation of low temperature preservation technology,has become a hot research direction because of its strong feasibility and good preservation quality,and has been widely used in the process of meat preservation.Chitosan coating preservation as an non-poisonous and efficacious new science,is coming in for more and more attention,for its preservation research mainly focus on fish products and specific species,the lack of research on shellfish aquatic products,and the incorporation of two kinds of fresh-keep technology impact on crustaceans storage quality of aquatic products also needs further research.This experiment by Chinese shrimps as the raw material,the study points technology combined with biological fresh-keeping agent on its storage quality,from the protein denaturation and degradation of the change of taste,smell and discussed the technology of Chinese shrimps quality keep internal causes,aimed at Chinese shrimp and shellfish aquatic product storage,preservation and character control to provide certain theoretical basis and reference.The main research results are as follows:(1)The temperature probe was used to determine the freezing point temperature of Chinese shrimps,and the character movements of Chinese shrimps under freezing temperature and cold storage were compared by monitoring sensory,physics and chemical,microbial indexes.The results showed that the freezing temperature of Chinese shrimps was about(-2.2±0.1)?.The total number of colonies(TVC),volatile base nitrogen content(TVB-N),thiobarbituric acid(TBARS)and SAP loss rate of cold storage group were higher than those of cold storage group.Sensory score in cold group was lower than the ice storage group.The color difference and texture properties(hardness,elasticity,adhesive viscosity and Chewiness)also showed different changes.The a*,b*and L*values of the freezing group were closer to those of the fresh samples,and the hardness,elasticity,adhesive viscosity and masticability were better.The shelf life of the refrigerated group was 5 d to 6 d,while the shelf life of the refrigerated group was 8 d to 10 d.The deterioration of sensory quality appeared in the cryogenic group in the middle and later period of storage,indicating that the preservation effect of cryogenic storage technology still needs to be further studied.(2)In order to further improve the storage quality of Chinese shrimps under freezing temperature conditions,the effects of chitosan coating combined with freezing preservation technology on the character of Chinese shrimps during storage were researched.The results revealed that at the end of storage,the thiobarbituric acid(TBA)value of Chinese shrimps coated with chitosan decreased by about 40%compared with the blank control group,and the lipid oxidation of Chinese shrimps was obvious restrain.In addition,p H value,total number of colonies(TVC),volatile base nitrogen content(TVB-N)and SAP loss rate of the samples all increased slowly,while color difference,sensory evaluation and chemical indexes changed less.The changes of water distribution and texture characteristics also showed that the chitosan composite coating could effectively inhibit the deterioration of shrimp quality.(3)The impacts of chitosan coating united with freezing technology on the preservation of texture and characteristics of Chinese shrimps were studied by using the basic nutrients,protein functional properties,protein denaturation and degradation,and the changes of muscle structure of Chinese shrimps.The results showed that the protein content of Chinese shrimps was 22.35%.The analysis of protein biochemical characteristics showed that the salt solubility,sulfhydryl content and Ca2+-ATP activity of actomyosin could be delayed by chitosan composite coating,and protein denaturation could be effectively controlled by chitosan composite coating.SDS-PAGE gel electrophoresis showed that chitosan composite coating could inhibit protein degradation.Muscle microstructure(MFI)was changed,the muscle segment space was enlarged,and the proportion of muscle tissue area decreased less than that of the single coating group and the other group,indicating that the freshness of shrimp body was in a good state.(4)The effect and mechanism of chitosan composite coating combined with freezing technology on the retention effect of Chinese shrimps were studied by measuring the sensory evaluation of Chinese shrimps'flavor and analyzing the flavoring odor.The results showed that the flavor sensory score of chitosan composite coating decreased the slowest.Electronic nose analysis shows that in Loading analysis,sensor R(7)W1W has the largest contribution rate,followed by sensor R(2)W5S,and sensor R(9)W2W and sensor R(4)W6S have similar contribution rate.Principal component analysis(PCA),linear discriminant analysis(LDA)and radar map analysis showed that at the end of storage,the odor characteristics of chitosan compound group were most similar to those of fresh samples,which could effectively maintain its inherent flavor.In addition,the results of electronic tongue also showed that the change of taste was mainly contributed by the first principal component,and the change of taste in each group was small within 0 to 4 days.With the prolongation of storage time,the change trend of umami and saltiness appeared different. |
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