| Procambarus clarkia is also called crayfish,which taste is delicious,unique flavor,high protein but low fat.It is the Chinese most popular product on the market of freshwater shrimp.The crayfish in China has strong regionalism and seasonality.At present,its products are mostly treated by high temperature and high pressure sterilization,which seriously affects the texture of products,and the loss of nutritional components is also serious.The exported crayfish products mainly include frozen lobster,frozen whole lobster and other frozen products.After cryopreservation,the loss of protein and moisture in shrimp tissues is large,which weakens the original flavor and taste of fresh lobster,and has a large nutritional loss.The content of water and protein in crayfish is high,so it is easily corrupted by microbial contamination,and the shelf life of its products is often shorter.Aiming at the problems in the market of crayfish products,the aim of this study is to develop a low temperature pasteurization and long shelf life of crayfish products in chilled condition.The main results were presented as follows:1.The vacuum packed crayfish conditioning products were stored at the end of the shelf at 4℃.Then isolated the main spoilage bacteria from the products and 85 isolates of spoilage bacteria were divided into 5 groups by observing the colony morphology.Then the representative strains of each group were selected for physiological and biochemical experiments and 16SrDNA identification.The results showed that the 5 dominant spoilage bacteria were Bacillus cereus,Bacillus methylotrophicus,Staphylococccus wameri,Lysinibacillus fusiformis,and Macrococcus caseolyticus.The decay ability of 5 spoilage bacteria was determined and the results were A31,E3,D10,A7and A24.Therefore,Bacillus cereus(A3l)and Macrococcus caseolyticus(E3)were selected as the main spoilage bacteria in the crayfish conditioning products to do the later experiments.2.Take the Bacillus cereus and Macrococcus caseolyticus as indicative bacteria,four kinds of preservatives were selected from 16 kinds of spices and 5 common natural preservatives.They were cinnamon,octagonal,TP,and ε-PL.Four kinds of preservatives were carried out in orthogonal experiment to obtain the optimum compound ratio as:0.02%ε-PL+3%cinnamon+0.5%TP+1%octagonal.Then the activity of compound preservatives was studied and it was found that the activity was not affected by the temperature and pH,and the metal ions had a certain effect.3.The compound preservative agent was applied to the two dominant spoilage bacteria.It was found that UV absorption,electrical conductivity,soluble sugar content,soluble protein content and AKP enzyme activity increased,and cell membrane permeability and cell wall integrity changed,which indicating that compound preservative had certain damage to the bacteria.The effect of compound preservative on bacterial cell apoptosis was detected by Annexin V-FITC/PI staining.It was found that the rate of apoptosis of Bacillus cereus was 88.1%,and the apoptosis rate of Macrococcus caseolyticus was 63%.it revealed the compound preservatives had a significant effect on bacterial cell apoptosis.4.The compound preservatives were applied to the conditioning products of crayfish.Through the determination of basic nutrients,it was found that adding compound preservative did not affect the basic nutrients of crayfish.The amino acid,fatty acid and mineral elements of two kinds of products were analyzed by the control group and the preservative group.It was found that the composition of amino acids in the two groups of shrimp meat was all comprehensive,balanced and with good flavor.The quality of fat in shrimp meat was high and no significant difference in the content of mineral elements in the two groups.5.The compound preservatives were applied to the conditioning products of crayfish.The sensory evaluation of products showed that compound preservatives can effectively maintain the sensory quality of products,so that their sensory quality was still within acceptable range for a long time.The total number of colonies,texture,TVB-N,TBA,pH,water holding capacity and microstructure were studied from two groups of product.It was found that compound preservative can significantly reduce the growth of microbes and TVB-N during storage,delay the deterioration of texture and microstructure,restrained the TBA and pH increased and maintained the water holding capacity.Therefore,the shelf life of the products was extended.Finally,through the analysis of different content of biogenic amines in two groups of products during storage,the characteristic biogenic amines in crayfish products during storage were tryptamine,putrescine,cadaverine,histamine.The four kinds of biogenic amines were considered as a reference index in the evaluation of their quality. |
