Effects Of Frozen Storage Conditions On Lipid Oxidative Stability And Flavor Quality Of Eriocheir Sinensis Hepatopancreas

Chinese Mitten Crab（Eriocheir sinensis）is deeply loved by consumers because of its high nutritional value and unique flavor.At present,river crabs on the market are mainly circulated in the form of live productsand are listed intensively in the early winter of each year.Therefore,the selection of processing and preservation methods of crabs and the preservation of characteristic quality of river crabs have become the technical requirements for the sustainable and healthy development of the industry.Among them,the quality changes of cultured Eriocheir sinensis,especially the influence of hepatopancreatic lipids on its flavor is very important.The hepatopancreas of Eriocheir sinensis cultured in Chongming area were taken as the main research object.Firstly,the indexes related to lipid oxidation of hepatopancreas were compared and analyzed,and accurately predicted by artificial neural network model;At the same time,the changes of lipid stability of frozen hepatopancreas were characterized by Tri-stepinfrared spectroscopy.Next,the flavor components of hepatopancreas during frozen storage were compared and analyzed.Sensory evaluation was carried out at the same time.Finally,the sensory comprehensive score and fuzzy logic model were used to construct the flavor evaluation model of frozen hepatopancreas,which provided basic parameters for the low-temperature circulation of Eriocheir sinensis.The main research contents and results are as follows:（1）Effect of frozen storage on lipid oxidativestability of hepatopancreas of Eriocheir sinensis The changes of lipid oxidation stability of hepatopancreas under different frozen storage conditions（temperature and time）were observed and analyzed.Firstly,the indexes related to lipid oxidation of hepatopancreas（peroxide value,acid value,anisidine value and thiobarbituric acid value）were measured.Lipid oxidation of hepatopancreas of Eriocheir sinensis under different frozen storage temperatures（-20℃,-40℃,-80℃）and freezing storage time（up to 16 weeks）.Under the same frozen time,the peroxide value,acid value,anisidine value and thiobarbituric acid value of the sample group frozen at-80℃were the lowest than those frozen at-20℃and-40℃,and the frozen storage slowed down the occurrence of lipid oxidation reaction.In addition,based on storage temperature and time,BPNN can accurately predict the lipid oxidation of hepatopancreas of Eriocheir sinensis;At the same time,the fatty acid composition of hepatopancreas was measured and combined with atherosclerosis index（AI）and thrombus index（TI）to evaluate the nutritional value and safety of hepatopancreas during frozen storage.During frozen storage,the content of saturated fatty acids in hepatopancreas increased,while the content of monounsaturated fatty acids and polyunsaturated fatty acids decreased,resulting in a significant increase in AI and TI.Secondly,the changes of lipid oxidation stability of hepatopancreas during frozen storage were characterized by Tri-step infrared spectroscopy.With the extension of frozen storage period,the spectral difference of hepatopancreas increased significantly.Firstly,FT-IR showed that the peaks appeared at 2924 cm^-1,2854 cm^-1,1745cm^-1,1641 cm^-1,1461 cm^-1 and 1158 cm^-1;Secondly,SD-IR further improves the spectral resolution.The peak differences at 2924 cm^-1,2854 cm^-1,1745 cm^-1and 1452 cm^-1 became more obvious;Finally,the samples with different frozen temperatures were further distinguished by observing the intensity of 2DCOS-IR automatic peak.（2）Effect of frozen storage on flavor quality of hepatopancreas of Eriocheir sinensis The changes of hepatopancreas flavor under different frozen storage conditions（temperature and time）were observed and analyzed.Firstly,the flavor related indexes of hepatopancreas（fishy substances,free amino acids and flavor nucleotides）were measured.During frozen storage,the contents of fishy odorsubstances,free amino acids and flavoring nucleotides increased gradually.Compared with-20℃and-40℃frozen storage groups,the contents of fishy odorsubstances,free amino acids and flavoring nucleotides in-80℃frozen storage group increased the least,and frozen storage slowed down the degradation of protein and ATP;At the same time,sensory evaluation of odorand taste was carried out to directly reflect the flavor changes of hepatopancreas during frozen storage.The results of sensory evaluation showed that the odor sensory score decreased graduallywith the extensionof frozen storage period,the sensory score of umami,sweetness and saltinessdecreased,and thesensory score ofbitterness increased.Combined with the odor intensity value（OAV）and the taste intensity value（TAV）,the key flavor compounds were characterized.The key substances affecting the flavor of hepatopancreas during frozen storage were selected:1-octene-3-ol,hexanal,nonanal,lysine,histidine,valine,methionine and hypoxanthine.（3）Construction of flavor evaluation model of frozen Eriocheir sinensis hepatopancreas Based on the experimental results,hexanal,histidine and hypoxanthine were selected as the input variables of the fuzzy logic model,and12 flavor grades were selected as the output variables of the fuzzy logic model.When frozen hepatopancreas was stored at-20℃,-40℃and-80℃,the Pearson correlation coefficients R between frozen storage time and flavor grade of frozen hepatopancreas were 0.99,0.99 and 0.97,respectively;The Pearson correlation coefficients R of sensory comprehensive score and flavor grade were-0.97,-0.98 and-0.97,respectively.The flavor quality of frozen hepatopancreas can be successfully evaluated by using fuzzy logic model.In conclusion,this study selected female Eriocheir sinensis hepatopancreas rich in oilwere frozen at-20℃,-40℃and-80℃for 16 weeks.The lipid stability and flavor quality of Eriocheir sinensis hepatopancreas frozen at-80℃were better than those frozen at-20℃and-40℃.Based on the lipid oxidation index,the prediction model of hepatopancreas lipid oxidation under frozen storage was established.At the same time,the flavor evaluation model was constructed based on sensory comprehensive score and fuzzy logic model to provide basic parameters for low-temperature circulation of Eriocheir sinensis.