Study On Contribution Of Chinese Mitten Crab(Eriocheir Sinensis) Gonad Lipids To Gonad Aroma

Chinese mitten crab has four edible parts: abdomen, claw, leg and gonad. Gonad is one of valuable and traditional aquatic products, which is quite popular among consumers due to its special flavor. Besides, gonad is rich in lipids and has abundant of fatty acids and nutrients. However, little is known about the precursor substance of the gonad aroma and whether this aroma is associated with gonad lipid or not. Eriocheir sinensis gonad lipid was used as the research object in this paper. Firstly, volatile flavor of the gonad before and after cooking or before and after extracting lipids, were evaluated by sensory analysis, Electronic Nose technology and GC-MS, respectively. Secondly, lipid content as well as total, neutral and polar fatty acids contents in gonad were identified and analyzed, respectively. The results are as follows:1. The Chinese mitten crab gonad was defatted by chloroform with methanol. The results of sensory analysis were significantly different when the lipid was removed. The volatile flavor composition of control held an absolute advantage over the treated samples both in variety and content during analysis of gas chromatography-mass spectrometry(GC-MS), which especially reflected in Aldehydes, Alcohols, Furans, N-containings, and S-containings. The principal aroma analysis showed that the changes of Pentanal, 3-Methylbutanal, 2-Methylbutanal, Benzeneacetaldehyde, 2-Nonanone, 2-Ethylfuran, 2-Pentylfuran Dimethyldisulfide were significantly different between the treated samples and control. As a result, we speculated that the eight kinds of principal aroma compounds may be produced by the lipid oxidation degradation of flavor precursor substances, and might be one of the major reasons leading to aromas difference in oil, meatbetween samples before and after the removal of the fat.2. Sensory evaluation and volatile components were conducted and measured in gonads of Chinese mitten crabs before and after cooking. Gonads of crabs were cooked and subjected to sensory evaluation and electronic nose experiment, respectively. The results showed there was a significant difference between the two samples in sensory evaluation. Odor discrimination is mainly reflected in flavor of meat, barbecue, nutty and grassy. Totally 62 volatile compounds were identified by GC-MS. There was a significant difference between raw and cooked gonads. A large number of Aldehydes, Furans, N-containings, S-containings were produced during cooking, such as 3-Methylbutanal, 2-Methylbutanal, Octanal, 2-Pentylfuran, Dimethyldisulfide, which also have high OAVs and play an important role in gonads aroma.3. The contents and components of lipid were analyzed by Rod-TLC and GC-MS. The results showed that they have a relatively similar lipid element. The total lipids are composed of triglycerides, polar lipids and cholesterol. Triglycerides were the main lipids components of which the contents were as much as 94.59%-99.60%. The lipid contents in fresh gonads were higher than that in gonads after cooking. It indicated that lipids might transform into volatile components during cooking.Volatile substances in lipids of gonads were measured by GC-MS. Aldehydes and aromatics were the main volatile components, which accounted for about 60% of the total content.4. Total lipid(TL), neutral lipid(NL), phospholipid(PL) and fatty acids distribution characteristics of female and male gonads were analyzed, respectively. The results showed that the contents of unsaturated fatty acids were far more than that of saturated fatty acids contents, and the highest content was monounsaturated fatty acids. The content of total fatty acids after cooking reduced. The content of neutral lipid fatty acids in male gonad decreased by 14.28 mg/g, and the content of phospholipid fatty acid did not change significantly. Changes of neutral lipid fatty acids and phospholipid fatty acids in female crab were both obviously observed, reducing by 15.93 mg/g and 5.93 mg/g, respectively. There is a significant change Oleic acid, linoleic acid, Linolenic acid and palmitic acid, which may be closely related to flavor.