Study On The Variations Of Flavor Substances In Fermentation Process Of Sichuan Bran Vinegar

With a considerably long history, Vinegar production played an important role in the culture of China. As a sour condiment in daily life, the flavor of vinegar needs to be full-bodied and harmonious. Acclaimed as one of the most famous vinegars in China, Sichuan bran vinegar is produced by conventional solid-state fermentation. The success of open solid-state fermentation depended on the conjunct fermentation by various microbes from environment. The flavor substances generate and change complexly in the process of fermentation and aging as the change of microbes is complex. In this thesis, the flavor substances of vinegar cultures were examined by head space-solid phase micro-extraction-gas chromatography-mass spectrum(HS-SPME-GC-MS)and high performance liquid chromatography(HPLC), the changes of flavor substances of vinegar cultures were clustered by SPSS 15.0. The main results were as follow:1. Changes of physicochemical indexes in fermentation and agingThe changes of some physicochemical indexes include total acidity, involatile acids, formaldehyde nitrogen, dissoluble saltless substance, reduced sugars in fermentation and aging were detected continuously. The total acidity, formaldehyde nitrogen and dissoluble saltless substance increased through out the fermentation period, while the reduced sugars decreased in the same time. The color of vinegar culture is getting darker as well. In the aging period, formaldehyde nitrogen and reduced sugars declined slightly. Dissoluble saltless substance increased in the beginning of aging, but felt if the aging is too long. Involatile acids increased significantly in the beginning of fermentation, but decreased after that. The pH value decreased firstly, then fluctuated in the rest time of fermentation and aging. The color of culture turned into dark brown after a two-year aging. 2. Changes of organic acids in fermentation and agingAcetic acid and lactic acid were important organic acids with the largest content. Acetic acid increased rapidly from 103.99 mg per 100g culture to 3593.34 mg/100g culture, especially in the first 7 days. The content of acetic acid decreased slightly in the aging; it felt to 3362.08 mg/100g culture after a 48-month aging. Lactic acid increased quickly during the form days, but decreased to 856.09 mg/100g culture after a 6-month aging. It felt slightly in the rest of aging. Tartaric acid increased in the first place and decreased then, however, the change was not very big. Pyruvic acid increased in the fermentation period, and remained stable in the aging period. Citric acid and malic acid showed a downward trend along with the process of fermentation and aging, whereas oxalic acid did not change significantly.2. Changes of volatile compounds in fermentation and agingThe volatile compounds of Sichuan bran vinegars in fermentation and aging were isolated by headspace solid phase micro-extraction, analyzed using GC-MS, and clustered by SPSS 15.0. The kinds and total peak area of volatile compounds of Sichuan bran vinegar increased in fermentation period and the beginning of aging, however, it decreased gradually after that. first month of Matlab 7.0,we can knew somethings about changes of volatile compounds. Esters and ethanol decreased in the whole process, phenethyl alcohol increased in the fermentation and reached the peak after a 1-month aging. The kinds of acids were small in fermentation; the content of long-chained acids increased in the aging period. Aldehydes, ketones and heterocyclic compounds increased in the aging, especially the content of pyrazines.