Studies On Aroma Compounds Of Chinese Soy Sauce Aroma Type Liquor

Soy sauce aroma type liquor is one of five categories classified according to aroma characteristics of Chinese liquor. It possesses distinct flavor due to the unique natural environment and peculiar manufacturing practice, involving higher temperature of qu-making, staking of fermenting grains, fermentation, distillation, and longer time of storage. The volatile composition of Chinese liquor is quite complex, especially for soy sauce aroma type liquor. Therefore, the key aroma compounds of soy sauce can not be identified until now. The objective of the present research is to apply SPE method combined with GC-O for the analysis of volatiles in Chinese soy sauce type liquors. Moreover, it is expected, through employing SBSE followed by GC–MS for quantification and discriminant analysis for comparison of soy sauce aroma type liquors and Daqu, the findings will help to a better understanding of baijiu (Chinese liquor) and find out the key aroma compounds of soy sauce arom type liquor. The main contents are as follows:(1) In SPE method, Chinese liquor was fractionated on a bed packed with 1.6 g of Lichrolut-EN resins and four solvents of increasing strength was applied to elute the aroma compounds from the column. The result showed that fraction1 was enriched in esters. Fraction2 concentrated the alcohols and some other compounds of intermediate polarity, while fractionation3 was enriched in fatty acids. The results revealed that the proposed procedure allowed for a feasible and effective fractionation of Chinese liquor. In addition, fractionation through solid phase extraction could be used as a tool to simplify the chromatogram for peak identification and facilitate the GC-O analysis.(2) The aroma compounds of soy sauce aroma liquor was analyzed by SPE method followed by GC-O and a total of 126 aroma compounds were identified. The results revealed that some compounds, such as ethyl acetate, ethyl 3-methylbutanoate, ethyl hexanoate, 2-butanol, 2-methylpropanol, 3-methylbutanol, isobutyric acid, ethyl benzoate, ethyl phenylacetate, 2-pentanone, 3-octanone, 2,5-dimethylpyrazine, 2-acetylfuran, 1,1-diethoxyethane and dimethyl trisulfide, had relatively stronger GC-O intensity than other compounds and contributed a lot to the Chinese liquor aromas.(3) Stir bar sorptive extraction (SBSE) method, a simple, cost-effective, and reliable method, was applied to the analysis of soy sauce aroma type liquor. To optimize the extraction conditions, several parameters were explored, including Twister size, ethanol content, and extraction time. Based on the results of optimization, the original baijiu samples were diluted with deionized water to a final concentration of 10%vol ethanol, and then extracted by a 10 mm×0.5 mm Twister for 90 min.(4) The aroma compounds of soy sauce type liquor were quantified by SBSE method combined with GC-MS. In this study, a total of 76 volatile compounds were quantified with SBSE method. Quantification results indicated that the volatile profiles of different aroma type Chinese liquors and the concentrations of some aroma compounds were quite distinct. For example, LJ-CT had the highest level of aromatic compounds; the concentration of furans in KZJ and YQ was much lower than that in LJ; LJ had higher level of pyrazines than KZJ and YQ. Based on the concentration and threshold of each aroma compound, it was discovered that ethyl hexanoate, 3-methylbutanal,β-damascenone and dimethyl sulfide contributed the most to the aroma, followed by ethyl 3-phenylpropanoate and 4-methylphenol. 3-methylbutanol;hexanoic acid and furfural also contributed to the aroma of Chinese soy sauce liquor. According to the results from discriminant analysis, it was discovered that LJ liquors with soy sauce aroma could exhibited more prominent sauce flavor through extending the time for storage. In addition, the unique manufacturing practice of Chinese soy sauce aroma type liquor was responsible for its soy sauce flavor.(5) Soy sauce aroma type liquors from different years were quantified with SBSE method. The results revealed that the concentration of esters and alcohols was decreased with earlier production year. Moreover, the level of nitrogen-containing compounds and phenols was increased markedly. Some compounds, such as 2,3,5,6-tetramethylpyrazine and guaiacol, had bioactive function. Therefore, the bioactive function of Chinese liquor with earlier production year was enhanced. Based on the conclusion above, soy sauce aroma could exhibited more prominent sauce flavor through extending the time for storage. The reduction of esters and alcohols and increase in nitrogen-containing compounds and phenols was beneficial for enhancement of soy sauce aroma.(6) Stir bar sorptive extraction (SBSE) method was applied to the analysis of soy sauce aroma type Daqu. To optimize the extraction conditions, several parameters were explored, including Twister size, solvent, and extraction time. Based on the results of optimization, the original Daqu samples were immersed with deionized water overnight, and then extracted by a 10 mm×1 mm Twister for 60 min.(7) The aroma compounds of soy sauce type Daqu were quantified by SBSE method combined with GC-MS. A total of 87 aroma compounds were identified and quantification results indicated that the volatile profiles of different aroma type Daqu and the concentrations of some aroma compounds were quite distinct. By discrimination analysis, the ten Daqu samples could be classified into four groups according to the production area, degree of grinding and aroma type.(8) The quantificaiton results from SBSE method revealed that the level of furfural was the highest in soy sauce aroma type liquor. Some experts speculated there was some relationship between furfural and soy sauce aroma. In addtion, It was indicated that furfural helped restrainting the growth of Saccharomyces and output of Chinese liquor. Moreover, the former research discovered the content of furfural was dramatically decreased during the storage of fermented grains. In this study, strain which was isolated from the fermented grains of Chinese soy sauce style liquors showed efficient degrading ability against furfural. Moreover, the stain was identified as Paecilomyces variotii through sequencing and sequence contrast (DNA extracted by benzyl chloride method). GC-MS was used to quantitafied the concentation of furfural and furfural alcohol in the samples of different phase of the whole degrading process. The results proved that microorganism played a role in degrading furfural during the storage of fermentaed grains.