Analysis Of Non-volatile Organic Acids In Baijiu And Its Effects On The Flavor Of Baijiu

Organic acids have essential effects on the flavor of Baijiu.Except for some small molecular organic acids,which are volatile,most of other organic acids are non-volatile.And due to their diverseness and low contents in Baijiu,the detection of non-volatile organic acids(NVOAs)in Baijiu is still a challenging work.As an important part of non-volatiles,NVOAs have important contributions to the flavor of alcoholics.The NVOAs in Baijiu were mainly influenced by fermentation process and microorganisms.Therefore,the NVOAs in different types of Baijiu may vary greatly,they are possible to be used in terms of quality control,differentiation and can help us understand the differences among diverse flavors of Baijiu more comprehensively.Herein,a derivatization method coupled with GC-MS was applied for the detection of NVOAs in different flavor types of Baijiu.Principal component analysis(PCA),partial least-squares discriminant analysis(PLS-DA),heatmap and hierarchical clustering analysis(HCA)were used to analysis the NVOAs in different Baijiu further.And the results showed that NVOAs had great discrimination power to differentiate Baijiu.Besides,the flavor contribution of NVOAs to Baijiu and the perceptual interactions among NVOAs and volatiles were studied.The main contents are as follows:(1)An optimized derivatization method was developed to detect the NVOAs in Baijiu.Optimization on the reaction time and temperature revealed that 10 m L of Baijiu was concentrated to dryness,followed by adding 100μL BSTFA(bis(trimethylsilyl)trifluoroacetamide)and 50μL pyridine and subsequent derivatization over 3 h at 80°C was suitable.Under the optimal conditions,excellent linearity for all NVOAs was obtained with determination coefficients of R~2?>?0.99,the LODs were between0.05 and 11.75μg/L,inter-day and intra-day precision were below 7.30%and 6.90%,respectively,and recovery rates were in the range of 80.64–113.46%.Thirty-one NVOAs in soy sauce(SS),strong(ST),and Laobaigan(LBG)flavor-types of Baijiu were quantified.The concentration of lactic acid among the three types of Baijiu was the highest,whose contents were(1069.16?±?58.74,7330.11?±?47.67,2054.02?±?54.15)mg/L in LBG,SS,and ST,respectively.Besides,the NVOAs in these three Baijiu were quite different according to principal component analysis and hierarchical cluster analysis,which further confirmed the effectiveness of the NVOAs for distinguishing different flavor of baijiu.(2)Non-volatile organic acids(NVOAs)in 12 main flavor types of Baijiu were analyzed by a derivatization method combined with GC-MS and 38 NVOAs were quantified.Meanwhile,a flavoromics strategy based on the contents of NVOAs in the 12 flavor types of Baijiu was successfully used to the differentiation of Baijiu.From the perspective of the total concentrations of the NVOAs in the 12 flavor types,the Soysauce and the Sesame flavor types contained more NVOAs than other types,while the total concentrations of NVOAs in Rice,Feng,Light and Laobaigan were relatively low.PLS-DA models(explained variation,predictive capability)were used to consider different categories:fermentation process(0.931,0.870),starter(0.921,0.834),fermentation container(0.899,0.810)and raw material(0.951,0.909).Based on the selected categories,suitable separations were achieved,and most Baijiu can be predicted successfully in the prediction model.Seventeen potential markers in the four fundamental flavor types of Baijiu(Soysauce,Strong,Light and Rice)were identified by variable importance in projection method and were further processed using heatmap and hierarchical cluster analysis,indicating that the NVOAs had great discrimination power to differentiate Baijiu.(3)NVOAs associated with the Laobaigan flavor type of Baijiu were analyzed by a derivatization method,and 37 NVOAs were quantified.In addition,33 odorants were judged to have high flavor dilution factors by application of aroma extract dilution analysis(AEDA)and quantification by gas chromatography coupled with mass spectrometry(GC–MS)and GC combined with quadrupole time-of-flight MS(GC-QTOF MS).Among the 33 odorant compounds,22 were further verified as important aroma-active compounds in the tested LBG sample because their OAVs≥1.The quantitative data obtained for the odorants and NVOAs were used to recombine the overall flavor of Baijiu.The odor of the reconstitution of the odor-active volatiles and the NVOAs was more similar to that of the original Baijiu sample than the sample that only contained odor-active volatiles,and the alcoholic and sweety flavor odor characters were reduced,while others,that is,fruity,acidic,floral,jujube and grain,were amplified.(4)By application of aroma extract dilution analysis,a total of 13 esters in Laobaigan flavor type of Baijiu were judged with high FD factors and quantified using GC-MS.Among the 13 esters,9 were further verified as important aroma-active compounds in the tested LBG sample because their OAVs≥1.Besides,35 non-volatile organic acids were quantified by a derivatization method combined with GC-MS.Ethyl lactate and ethyl acetate were selected as the representative ester compounds.Lactic acid,the highest content of NVOAs in Baijiu,was selected as the representative organic acids.The perceptual interaction of lactic acid and ethyl lactate,and that of lactic acid and ethyl acetate were studied through the olfactory threshold.After adding lactic acid,the olfactory threshold of ethyl lactate and ethyl acetate were decreased obviously,which revealed that lactic acid gave additive or synergistic odor effects for these two esters.A derivatization method combined with GC-MS to analysis non-volatile organic acids in Baijiu was demonstracted.And this study had a relatively comprehensive understanding of the NVOAs in the 12 flavor types of Baijiu,and the adopted strategy using NVOAs to differentitate Baijiu has been proved to be a promising and powerful tool.Besides,the important influences of NVOAs to the flavor of Baijiu had been demonstrated.