Identification Of Key Odorants In Steamed Chinese Mitten Crab

Aquaculture of Chinese mitten crab(Eriocheir sinensis) is spread all over China nowadays. According to the statistics report, the annual output of Chinese mitten crab was over 720,000 tons in 2014, generating huge economic benefits. Yangcheng lake in Jiangsu province is the most famous crab producing area in China. E. sinensis is regarded as a favorite aquatic food for Chinese consumers due to its unique pleasant aroma and intensive umami taste. Many researchers have previously revealed the volatiles in E. sinensis. It could be easily found that most studies only focused on the characterization of odorants in crabs. Almost none of them identified the key odorant in E. sinensis, and important odorants were not verified by the analyte standards. It could be concluded that the identification of key odorants in Chinese mitten crab is not complete.In order to gain a deeper insight into the constitution of the aroma in E. sinensis and provide guide for the identification of key odorants in E. sinensis. Gas Chromatography/Mass Spetra-Olfactory was applied to identify the key odorants in the gonad part and abdomen meat of E. sinensis. It main results were listed as follows:(1) Optimization of analytical methods based on the known one. First of all, the temperature and time of extraction were optimized. The results showed that extracting at 80℃ for 30 minutes could get the best extraction efficiency. Second, it could avoid olfactory fatigue for assessors when took slower temperature rate. Third, assessors was trained systematically according to the national standard. Besides, qualification and quantitation method was build, the data of recovery rate and relative standard deviation showed the method was useful.(2) The gonad part of steam Chinese mitten crab was analyzed by sensory evaluation and GC/MS-O. The results of sensory evaluation showed that the typical aroma in the gonad part were strong fatty aroma, with moderate fishy aroma and egg yolk-like aroma as well as weak earthy aroma and meat aroma. Samples could be distinguished by sex from baking aroma and sweet aroma. 24 odorants were selected from the gonad part of steamed Chinese mitten crab by the method of AEDA. Among all the identified compounds, 6 of them were aldehydes, 2 of them were nitrogen containing compounds, 1 of them was alcohol compound, 3 of them were aromatic compounds, 3 of them were ketones, 2 of them were alkanes. Trimethylamine and benzaldehyde could be considered to be important odorants due their high dilution factors(FD=150:1). Modified frequency method was used to rank the top ten powerful odorants from 24 volatiles. The most intensive compounds were: trimethylamine, 3-methylbutanal, 1-penten-3-ol, toluene, ethylbenzene, p-xylene, n.i.(No.12), benzaldehyde, 6-methyl,5-hepten-2-one, acetophenone, undecane, decanal. Compared the results from OAV, 3-methylbutanal could be considered to be the key odorant contributing fatty aroma to the gonad part of steamed Chinese mitten crab, trimethylamine could be the key odorants contributing to fishy aroma, decanal could be considered having a close relationship with earthy aroma.(3) The abdomen meat of steam Chinese mitten crab was analyzed by sensory evaluation and GC/MS-O. The results of sensory evaluation showed that the typical aroma in the abdomen meat were strong meaty aroma, with moderate fishy aroma and sweet aroma as well as weak corn aroma, egg yolk-like aroma, earthy aroma and fatty aroma. 19 odorants were selected from the abdomen meat of steamed Chinese mitten crab by the method of AEDA. Among all the identified compounds, 3 of them were nitrogen containing compounds, 6 of them were sulfur containing compounds, 2 of them were aldehydes, 3 of them were aromatic compounds, 1 of them were ketones, 2 of them were alkanes. Trimethylamine could be considered to be the most important odorant due its high dilution factors(FD=150:1). Modified frequency method was used to rank the top ten powerful odorants from 19 volatiles. The most intensive compounds were: trimethylamine, toluene, n.i.(No.7), ethylbenzene, 2-ethylthiophene, p-xylene, 2,5-dimethylpyrazine, benzaldehyde, dimethyltrisulfide, 2-acetylthiazole, undecane, 2-decanone, dodecane. Compared the results from OAV, dimethyltrisulfide and 2-acetylthiazole could be considered as the key odorants contributing meaty aroma to the abdomen meat of steamed Chinese mitten crab, trimethylamine could be the key odorants contributing to fishy aroma, decanal could be considered having a close relationship with earthy aroma. 2,5-dimethylpyrazine could be the important contributor to corn aroma in the abdomen meat.