| Chinese liquor is a distilled liquor with a long history and world’s largest consumed spirit.Flavor plays an important role in consumer preference.The aroma of Chinese liquor is determined by thousands of volatile compounds commonly.However,the volatile components of Chinese liquor have not yet been fully understood,and its flavor function is still unclear.Traditional one-dimensional gas chromatography(1DGC)cannot meet the analysis of volatile components of complex samples such as Chinese liquor due to limited resolution.Comprehensive two-dimensional gas chromatography(GC×GC)has higher peak capacity,sensitivity and resolution than 1DGC,which is an effective means for analyzing complex samples.However,the application of GC×GC in Chinese liquor is still rare.Therefore,the purpose of this subject is to establish a GC×GC method suitable for qualitative and quantitative analysis of volatile compounds in Chinese liquor,on the basis of which a more comprehensive understanding of volatile components and flavor contribution in Chinese liquor is searched.The main research contents and conclusions are as follows.(1)Comprehensive two-dimensional gas chromatography/ time of fight mass spectrometry(GC×GC-TOFMS)data analysis method for volatile components in Chinese liquor is established.On the basis of mass spectrometry(MS)comparison,retention indice(RI)comparison is used.After verification by the standard,the accuracy of the RI comparison is highly reliable.The effects of three extraction methods head space solid-phase microextraction(HS-SPME),solid phase extraction(SPE)and stir bar sorptive extraction(SBSE)for the analysis of volatile components in Chinese liquor by GC×GC-TOFMS were compared.Significant difference was found for the extraction of various classes of compounds,so it is necessary for the analysis of volatiles in complex samples by combination of different methods.Twelve aroma types of Chinese liquor were analyzed by HS-SPME and SPE pretreatment combined with GC×GC-TOFMS.The GC×GC Chinese liquor flavor database is consists of 2,716 components with the information of identification data and aroma data.Dozens of potential aroma compounds was first found in Chinese liquor.(2)The effects of the parameters of HS-SPME on the analysis of trace components by GC×GC-TOFMS analysis in Chinesw liquor were discussed.It was found that the split mode injection would lose some information.When the sample was diluted to 2%vol alcohol content,the amount of trace components in Chinese liquor was the highest,and the peak area is the highest,which is conducive to the comprehensive qualitative and quantitative analysis of trace components in Chinese liquor.Combined with non-parametric tests,partial least squares discrimination analysis(PLS-DA),variable importance in the projection(VIP)value analysis and other multivariate statistical analysis methods,key characterized compounds were revealed.In this study,nine samples from strong aroma type liquors in Sichuan and Jianghuai were analyzed.With the above analysis methods,62 characteristic compounds were identified to clarify the chemical composition differences between the two kinds of samples.The content of furan and pyrazines compounds in Sichuan liquors is significantly higher than that of Jianghuai liquor.They are characteristic compounds of Sichuan liquor,which may have a certain relationship with higher koji-curing temperature.This method can explore the relationship between volatile compounds and liquor quality and aroma.(3)The effects of simulated matrix on the quantitative analysis of trace aroma components by HS-SPME-GC×GC-TOFMS methods were analyzed.Six compounds with higher content in Chinese liquor were added into the ethanol aqueous solution and configured into a more authentic simulated matrix.Compared with simple ethanol aqueous solution matrix,the linearity of quantitative standard curve was better and the quantitative concentration range was wider.A HS-SPME-GC×GC-TOFMS quantitative method was established for the determination of 125 trace aroma substances in Chinese liquor.The linearity,concentration range,limit of detection(LOD),limit of quantification(LOQ),repeatability and recovery were all in line with the quantitative requirements,and LOQ was about 1000 times lower than that reported in the existing literature.Trace aroma substances in strong aroma,light aroma and Chinese soy sauce type liquors were analyzed.The concentration of more than ten aroma compounds in Chinese liquor was quantified for the first time.Although the content of these compounds is low,the odor activity value(OAV)is larger than 1,which may contribute to the aroma of Chinese liquor.72 barley liquors brewed by different conditions were quantified by HS-SPME-GC×GC-TOFMS,combined with PCA analysis,it was found that the season factor were more important than the raw material factor and process factor for the change of flavor compounds content.It was determined that there were 59 compounds with significant differences of content in the samples brewed in different seasons.The average content of 28 aroma substances in each season’s samples is bigger than the aroma threshold,which may contribute to the difference in aroma characteristics between barley liquors brewed in different seasons. |
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