Characterization Of The Volatile And Aroma Profile Of Chinese Rice Wine

Aroma characteristic is one of the most important parameters for the quality of Chineserice wine, which greatly affects the choices of consumers. The aroma characteristic ofChinese rice wine is the result of the mixture and interaction of different aroma compounds.Characterization of the aroma profiles of Chinese rice wine is the precondition to modulatethe aroma characteristic of Chinese rice wine. It is very important for the improvement of thequality of Chinese rice wine. However, there are only a few researches have been carried outon the aroma composition of Chinese rice wine. The number and nature of the odorantsresponsible for the aroma characteristic of Chinese rice wine are still not known.The thesis is concerned with the volatile and aroma characteristics of Chinese rice wine.Modern flavor chemistry research approaches were employed to qualitatively andquantitatively measure the volatile and odor-active compounds in Chinese rice wine. We alsocompared the aroma profiles of different type Chinese rice wines and investigated theformation aroma compounds during Chinese rice wine manufacture. During the researchprocess new techniques and strategies were developed to deal with the technical challenges inflavor chemistry research. The main results were shown as follows:(1) A sensitive method for characterizing the volatile profile of Chinese rice wine usingcomprehensive two-dimensional gas chromatography coupled with time-of-flight massspectrometry (GC×GC-TOFMS) was developed for the first time. Comprehensivetwo-dimensional gas chromatography parameters were optimized for Chinese rice winevolatile compounds analysis. By combination of two sample preparation techniques andGC×GC-TOFMS, we investigated the detail of volatile profile of Chinese rice wine. A total of975volatile compounds were tentatively identified in Chinese rice wine, including93kindsof acids,149kinds of esters,61kinds of alcohols,52kinds of aldehydes,55kinds of acetals,98kinds of furans and lactones,42kinds of sulphur compounds,154kinds of nitrogencompounds,73kinds of ketones,46kinds of phenolics and152kinds of other compounds.The huge number of volatile compounds identified in Chinese rice wine showed the highlycomplex and diverse characteristics of Chinese rice wine.(2) New aroma extraction and pre-separation techniques for aroma composition researchin Chinese rice wine were developed in this study. LiChrolut-EN solid-phase extraction wasused to isolate the aroma components in Chinese rice wine. The results showed thatLiChrolut-EN had limited absorption of sugars, pigments, and other non-volatile compounds,while extracting a vast majority of polar and non-polar aroma compounds. This approach iseasy to use, labor-saving, solvent-saving and can be used to instead of traditional liquid-liquidextraction approach. A high-efficiency silica gel normal phase chromatography system wasdeveloped base on a fast protein liquid chromatography (FPLC) system. The newly developedsilica gel normal phase chromatography system overcame the disadvantage of traditionalsilica gel normal phase chromatography system, and could work automatically andgradiently.This system was very suitable for the pre-separation of complex aroma componentsin Chinese rice wine. (3) A total of90aroma compounds were identified in Guyuelongshan Chinese rice winesample by GC-O and GC-MS analysis, among them, nearly30kinds of aroma compoundswere identified in Chinese rice wine for the first time. In addition to acids, esters and alcohols,which commonly found in alcoholic beverages, benzaldehyde, vanillin, geosmin,γ-nonalactone, guaiacol,2,6-dimethylpyrazine and dimethyl trisulfide were identified to bepotentially important to Chinse rice wine. The aroma differences of Chinese rice winemanufactured with and without wheat Qu were investigated by aroma extract dilution analysis(AEDA). The results showed the aroma intensities of benzaldehyde, vanillin, geosmin, andphenolic compounds were much higher in Chinese rice wine manufactured with wheat Quthan that without wheat Qu. These aroma compounds might be the key aroma compoundswhich contribute to the characteristic aroma different of these two type Chinese rice wine.(4) A new strategy by combination of different quantitative methods was suggested forthe quantification of different aroma compounds in Chinese rice wine. By the combination ofHS-GC-FID, HS-SPME, SPE-GC-MS, and HS-SPME-GC-PFPD, a total of77aromacompounds were accurately quantified in Chinese rice wine.(5) The quantification and odor active values (OAVs) of Guyuelongshan Chinese ricewine showed that vanillin,3-methylbutanal,2-phenylacetaldehyde, dimethyl trisulfide,geosmin, guaiacol, benzaldehyde, and γ-nonalactone had important contribution to thecharacteristic aroma of Guyuelongshan Chinese rice wine. Comparison of the OAVs of aromacompounds between traditional and Qingshuang types of Chinese rice wines showed thatbenzaldehyde, γ-nonalactone, geosmin, guaiacol, vanillin, ethyl pentanoate, ethyl butanoate,ethyl3-methylbutanoate, ethyl hexanoate,3-methylbutanoic acid,3-methylbutanal, phenol,γ-nonalactone, and ethyl cinnamate were the most important aroma compounds responsiblefor the aroma profile differences between those two types of Chinese rice wine. Aromareconstitution model prepared by mixing aroma compounds quantified in Chinese rice wine inan odorless Chinese yellow rice wine matrix showed a good similarity to the aroma of theoriginal Chinese yellow rice wine.(6) The aroma characteristics of sweet-type Chinese rice wine were studied by sensoryanalysis, aroma extract dilution analysis (AEDA), and quantitative analysis. Sotolon wasidentified as key aroma compounds in Chinese rice wine for the first time. AEDA resultsindicated that sotolon (caramel-like) was the potentially key odorant responsible for thetypical caramel-like descriptor of sweet-type Chinese rice wine. The concentration of sotolonin Chinese rice wine was further quantified by Lichrolut-EN solid phase extraction coupledwith microvial insert large volume injection method. The content of sotolon that wasquantified ranged from35.93to526.17μg/L, was above its threshold (9μg/L) for all Chineserice wine samples. The highest concentration of sotolon was found in the sweet-type Chineserice wine, which highlighted the key aroma role of sotolon for this particular type of Chineserice wine.(7) The influence of yeast strains and wheat Qu on the Chinese rice wine fermentationand aroma compounds formation were investigated in this study. The volatile flavor profilesof the different Chinese rice wines showed statistically significant differences depending onthe yeast strains used. Yeast strains from the Shaoxing region showed a higher capacity to produce the esters, β-phenylethanol and3-methylthiopropanol, while yeast strains from theShanghai region stood out for their production of branched-chain higher alcohols. Chineserice wine fermented with a yeast strain from the Jiangsu region had the highest levels oforganic acids. The data obtained in this work shows that the yeast strains contributedsignificantly to the flavor differences of the Chinese rice wines from the different regions.Small-scale Chinese rice wine brewing showed that wheat Qu not only act as saccharifyingagent, but also can increase the yeast activity and the formation of aroma compounds. Higheryeast growth and fermentation rate, and lower yeast dead rate were observed when wheat Quwas used as saccharifying agent. Global analysis of the aromatic profiles revealed that the useof wheat Qu can greatly promote the aroma compounds formation in Chinese rice winefermentation. The total concentration of aroma compounds was1.40folds higher in Chineserice wine fermented with16%wheat Qu than the Chinese rice wine fermented with mixedenzymes. The concentrations of volatile phenolic compounds and higher alcohols wereobviously higher in Chinese rice wine samples fermented with wheat Qu. The role of wheatQu cannot be simply replaced by commercial enzymes, but the Chinese rice wine aromaticprofiles can be modulated depending on the amount of wheat Qu used in Chinese rice winefermentation.