| Chinese mitten crab(Eriocheir sinensis)has a high economic value due to its unique aroma and rich nutrition,which is an important freshwater aquaculture crustacean traditionally cultivated in China.The unique aroma is most contributed by its rich lipid and protein composition.Some studies have shown that phospholipids,triglycerides and free fatty acids are the three components that contribute the most to the aroma.Therefore,optimizing the steaming conditions of the gonads and hepatopancreas was the first step;and then electronic nose technology(E-nose)and gas chromatography mass spectrometry(GC-MS)were used to establish the thermal oxidation system(temperature,time,water content and oxygen)of key lipids;After heat treatment,lipid molecular species and fatty acid composition were determined to explore the regulation of thermal oxidation and degradation.The main research findings were as follows:1.The new adsorption material-Mono Trap,combined with gas chromatography mass spectrometry(GC-MS)was used to extract volatile compounds during the heat treatment of female crab gonads and hepatopancreas:(1)Volatile compounds reached the most abundant when the heating temperature and time were 100? and 25 min,respectively.(2)Heat treatment had a significant effect on the generation and enrichment of volatile compounds and the overall odor profile of the hepatopancreas was more abundant than the gonads.(3)The establishment of vitro model could provide a reaction condition for the research of oxidation degradation characteristics of lipids.2.Electronic nose combined with principle components analysis(PCA)and radar picture analysis was used to optimize water and oxygen of triglyceride(TG)and fatty acids(FFA)in gonads,phosphatidyl ethanolamine(PE)and fatty acids(FFA)in hepatopancreas.The results indicated that the optimal conditions of thermal oxidation and degradation were,TG in gonad: 100?,25 min,6 ?L water,aerobic conditions;FFA in gonad: 100?,25 min,8 ?L water,aerobic conditions;PE in hepatopancreas: 100?,25 min,0 ?L water,aerobic conditions;FFA in hepatopancreas: 100?,25 min,0 ?L water,aerobic conditions,respectively.3.The key lipid molecules and the characteristics of thermal oxidative degradation of lipids were studied,and the results were as follows:(1)Fatty acid content and composition in key lipids were declined after heat treatment.The oxidation and degradation of PUFA were prone to the formation of volatile compounds during the heating process.Among them,the content of DHA and EPA in TG decreased significantly(27.18% and 24.12%,respectively)before and after heat treatment.(2)The key fatty acids of TG are: C16:1,C18:2n6c,C20:4n6,C20:5n3 and C22:6n3;the key fatty acids of PE are: C18:1n9c,C18:3n3,C20:3n6,C20:3n3,C20:4n6,C20:5n3 and C22:6n3.(3)There were no significant changes in the molecular species of TG and PE after heat treatment,but the content of molecular species decreased significantly.(4)the unsaturation of fatty acids in TG acyl chain had a significant influence on TG molecular species,if the three chains in TG molecular species were all key fatty acids,they were the key TG molecular species: TG(16:1/20: 5/20:5),TG(16:1/22:6/22:6),TG(16:1/20:4/20:5),TG(20:5/18:2/20:4)and TG(16:1/18:2/20:5).(5)Thermal oxidation and degradation of lipids was affected significantly by unsaturation and carbon number of fatty acid.It will be more evident if fatty acids unsaturation of TG acyl chains or total carbon number increased.(6)The content of PE molecules species in the hepatopancreas was significantly decreased except for PE(16:0/17:0).Among them,the key PE molecular species was: PE(18:1/20:4). |
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