Characterization Of Non-volatile Gustatory Organic Acids And Polyhydroxy Compounds In Chinese Liquors

Chinese liquor,as a traditional distilled liquor,is one of the six oldest distilled liquors.Trace components which occupy 1%–2% of the liquor are important flavor compounds,and consist of volatile and non-volatile substances.Volatile compounds affect the aroma of Chinese liquor.According to foreign papers,we speculate that non-volatile compounds have impacts on the taste and mouthfeel of liquor,although they are odorless.So far,there were few reports about taste compounds in liquor.Besides,analyzing the effects of these compounds on liquor flavor from taste point of view had not been reported yet.Therefore,it is of great importance for a more comprehensive understanding of Chinese liquor and liquor quality control by researching types of non-volatile compounds in Chinese liquor,and exploring their influence on the taste of Chinese liquor.First,vacuum rotating evaporation and reversed phase-high performance liquid chromatography(RP-HPLC)were applied to separate the taste components in liquor.Then,ultra performance liquid chromatography(UPLC),liquid chromatographymass spectrometry(LC-MS)and derivatization with N,O-bis(trimethylsilyl)trifluoroacetamide(BSTFA)combined with gas chromatography-mass spectrometry(GC-MS)were used to identify non-volatile organic acids and polyhydroxy compounds.At last,determination of taste thresholds of taste compounds,recombination and omission experiments of taste were undertaken to evaluate the effect of non-volatile compounds on liquor flavor.The main contents are as follows:(1)Vacuum rotating evaporation and reversed phase-high performance liquid chromatography(RP-HPLC)were applied to separate the non-volatile taste components in liquor,and the taste components were separated into 11 fractions.Each fraction was removed solvent by vacuum rotating evaporation,and was dissolved in water,which was equal to the injection volume.Then,taste dilution analysis was applied to screen the sensory active fractions.The results showed that the non-volatile components of Chinese liquor were mainly sour.(2)Non-volatile organic acids and polyhydroxy compounds in 8 different aroma types Chinese liquors(strong aroma type,light aroma type,soy sauce aroma type,roasted sesame like aroma type,feng aroma type,chixiang aroma type,site flavor type,laobaigan flavor type)were identified by using BSTFA as derivatization regent coupled with GC-MS.A total of 48 non-volatile compounds were identified,including 28 non-volatile organic acids,15 polyhydroxy compounds,4 amino acids and 1 other type non-volatile compounds.The results showed that lactic acid has the highest concentration among all non-volatile organic acids,up to 461.2–1789 mg?L-1.The content of palmitic acid was the highest(25.98 mg?L-1)among the remaining organic acids,followed by 2-hydroxy-4-methyl pentanoic acid(10.84 mg?L-1).The results also showed much more hydroxy acids were detected and had higher levels,for example,glycolic acid,2-hydroxybutyric acid,4-hydroxybutyric acid,2-hydroxy-4-methyl pentanoic acid,and 2,3-dihydroxypropionic acid.Overall,most of the non-volatile organic acids had higher contents in soy sauce aroma type,roasted-sesame-like aroma type and chixiang aroma type Chinese liquor,and lower in light aroma type and feng aroma type Chinese liquor.The concentration of glucose was highest among 15 polyhydroxy compounds(4.338 mg?L-1),followed by glycerol(2.039 mg?L-1),fructose(1.055 mg?L-1)and sucrose(1.136 mg?L-1).Most of the polyhydroxy compounds had higher contents in site aroma type and strong aroma type Chinese liquor,and lower in light aroma type Chinese liquor.(3)Taste thresholds of 31 non-volatile compounds were determinated in water.The results showed that many non-volatile organic acids had two taste characteristics,for example,lactic acid showed sourness and astringency,and 2-hydroxy-4-methyl pentanoic acid showed sourness and sweetness.3-Phenyllactic acid showed sourness and astringency,and contributed to wood and rose like aroma.Besides,polyhydroxy compounds had higher taste thresholds than organic acids,which over 10000 μmol?L-1,except for fructose(6994 μmol?L-1).(4)Based on the quantitative results and relevant taste thresholds,Dose-over-Thresholds(DoT)of taste active compounds were calculated to analyze their contributions to the taste of strong aroma type finished liquor.In terms of sour taste,the DoT factors of lactic acid,2-hydroxy-4-methyl pentanoic acid,glycolic acid,2-furoic acid and succinic acid were over 0.01,and lactic acid had the highest DoT factors(DoT=3.72),which meaned lactic acid was important to the sour taste of Chinese liquor.Lactic acid,2-furoic acid and succinic acid had higher DoT factors from the standpoint of astringency,and the DoT factor of lactic acid was the highest(DoT=2.63),which showed lactic acid contributed to the astringency of Chinese liquor.In addition,from the perspective of sweetness,2-hydroxy-4-methyl pentanoic acid had the highest DoT factor,higher than the DoT factors of polyhydroxy compounds.The results showed 2-hydroxy-4-methyl pentanoic acid contributed to the sweetness of Chinese liquor,and polyhydroxy compounds had low impact on the sweetness of Chinese liquor.(5)Sour and astringent taste recombination were undertaken by adding 14 non-volatile organic acids which were identified before,and omission experiments were carried out according to their DoT factors,by missing those compounds with DoT<0.01,0.01<DoT<1 and DoT>1,respectively.The recombinates that omitted compounds with DoT<0.01 and 0.01<DoT<1,were considered a good similarity with the original sample for sourness and astringency,which meaned compounds with DoT<0.01,0.01<DoT<1 had low impact on the sour taste and astringency of Chinese liquor.The recombinate that omitted compounds with DoT>1,was lower in sourness and astringency.The results confirmed that lactic acid was the key taste active compound to the sour taste and astringency of Chinese liquor.