| The Chinese mitten crab(Eriocheir sinensis)is an important freshwater aquaculture product that is favoured by consumers for its delicate taste,excellent flavour and nutrition,and has a high economic value.Chinese mitten crabs are mainly sold live and their production areas are mainly located in the eastern part of China,so live crabs need to be transported over different distances and times to be sold nationwide and even worldwide.With the rapid development of the internet and e-commerce economy,the e-commerce delivery sales model is gradually taking over.Storage and transportation is an extremely important part of the Chinese mitten crab supply chain,so the changes in biochemical characteristics,nutrition and flavour quality of the crab during live storage and transportation need to be clarified.In this study,the mortality,vigor,physiological metabolism,nutritional quality and flavour quality of Chinese mitten crab were investigated during the storage and transportation process by simulating the conditions of e-commerce transportation and selecting four time periods: 0 h,24 h,48 h and 72 h.Firstly,the mortality rate and vigor of female Chinese mitten crab were counted and evaluated during the four time periods.At the same time,the changes of biochemical characteristics of Chinese mitten crab in the process of storage and transportation,were analyzed by glycogen,lactate,TVB-N,p H and adenylate energy charge.Then,the effects of storage and transportation period on nutritional quality of Chinese mitten crab were comprehensively evaluated by weight loss rate and proximate composition,amino acids and fatty acids in edible parts.Finally,the flavour quality of the edible parts of Chinese mitten crab was comprehensive evaluated,mainly through sensory evaluation of taste,determination of free amino acids and taste nucleotides,to analyse the effect of storage and transportation on the taste quality of Chinese mitten crab,and the sensory evaluation of odor and determination of volatile substances were used to analyse the effect of storage and transportation on the odor quality of Chinese mitten crab.The study can provide a theoretical basis for optimising the storage and transportation of Chinese mitten crab and its quality control.The main research contents and results are as follows:(1)Effects of storage and transportation on physiological metabolism of the Chinese mitten crab(Eriocheir sinensis).The study on mortality and vigor changes of Chinese mitten crab during storage and transportation by simulating e-commerce storage and transportation conditions such as packaging and transportation vibration found that after 24 hours of simulated transportation,there was no mortality and strong vigor;after 48 h,mortality was 3.33% and vigor decreased significantly(P<0.05);after72 h,mortality reached 40.00% and vigor was low.The study of physiological and metabolic changes of Chinese mitten crab found that after 24 h of simulated transportation,there were no significant differences in lactate,TVB-N and adenylate energy charge of the meat compared to the 0 h group(P>0.05),while the temperature inside the box increased in the later stages of transportation,the metabolism of crab was enhanced,glycogen was consumed in large quantities,metabolites such as lactate and TVB-N accumulated,and the energy homeostasis was disturbed,resulting in poor vigor and low survival rate.Therefore,to ensure low mortality and high vigor of Chinese mitten crab,the storage and transportation time needs to be controlled.(2)Effect of storage and transportation on nutritional quality of Chinese mitten crab(Eriocheir sinensis).As the storage and transportation time increased,the weight loss rate of Chinese mitten crab and its crude fat and ash content in the edible parts did not change significantly(P>0.05),while the crude protein content tended to increase and the moisture content tended to decrease.According to the results of the essential amino acid index,the meat and gonads maintained the nutritional quality of a high-quality protein source during storage and transportation,while the amino acid nutritional quality of the hepatopancreas decreased after 48 and 72 h of transportation(EAAI<0.95).The results for fatty acids showed that the quality of high-quality fatty acid sources was maintained in meat and gonads during storage and transportation,while the n-3/n-6 values of the hepatopancreas after transportation were significantly lower than 0 h group(P<0.05),indicating that the nutritional quality of fatty acids in the hepatopancreas decreased after simulated transportation.(3)Effect of storage and transportation on flavour quality of Chinese mitten crab(Eriocheir sinensis).The changes of flavor quality of Chinese mitten crab were comprehensively evaluated from the aspects of taste and odor,and the results of sensory analysis showed that the umami,sweet and salty taste of meat and the bitter taste of hepatopancreas of Chinese mitten crab decreased,and the bitterness of gonads was increased after simulated transportation.The umami taste of three edible parts tended to decrease as the transportation time increased,while the ammonia smell of meat and the fishy smell of gonads and hepatopancreas tended to increase.The results of physicochemical analysis showed that after simulated transportation,the content of umami free amino acids in meat of Chinese mitten crab decreased significantly(P<0.05),and its proportion decreased by about 38%(24 h),50%(48 h)and 50%(72 h),respectively,compared with the 0 h group,while the content of bitter free amino acids in gonads increased significantly,and the content of umami amino acids decreased with the increase of transportation time.The contents of umami amino acids in hepatopancreas decreased with increasing transportation time,with the proportion decreasing by 22%(24h),41%(48 h)and 53%(72 h),indicating that the current storage and transportation mode was not conducive to the accumulation of umami amino acids in Chinese mitten crab.The results of volatile compounds showed that,the content of nonanal and decanal,the main flavouring compounds in the meat of the Chinese mitten crab,tended to decrease as the transportation time increased,while the content of trimethylamine,which has an ammonia and fishy flavour,tended to increase,and the content of hexanal(grassy and fishy flavour)in the hepatopancreas tended to decrease,while the content of trimethylamine tended to increase.Therefore,the longer the time of storage and transportation,the umami flavor of edible parts of Chinese mitten crab decreased,and the ammonia flavor increased.To sum up,with the extension of storage and transportation time,the mortality rate of female E.sinensis increased significantly,vigor decreased significantly,metabolites accumulated in the meat,the nutritional quality of amino acids and fatty acids of the hepatopancreas decreased,the umami taste of the three edible parts was weakened and the off-flavours such as ammonia and fishy odors increased.Therefore,considering the mortality rate,vigor,nutritional quality and flavor quality of edible parts,the optimal storage and transportation period for Chinese mitten crabs under the current e-commerce storage conditions is 0-24 h. |
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