| Bitterness and astringency are the most common odor tastes in baijiu（Chinese liquor）,which directly affect the sensory quality and grade of baijiu.With the development of society and the increasing quality of people’s living standards,people begin to pay more attention to the quality and style characteristics of baijiu.As for the problems of bitterness and astringency in baijiu,experts and scholars have speculated that what substances may be present in bitter and/or astringent taste in baijiu basing on the production experience,and many researches were dedicated to the source of these bitter and/or astringent compounds.However,the composition of bitter and astringent in baijiu had not been very clear,the problem of removing or avoiding the bitterness and astringency of various types of baijiu were not solved well,and the bitter and astringent taste of baijiu was still a technical problem.To explore the composition of bitter and/or astringent taste compounds in baijiu,in this study,vacuum rotary evaporation was used to determine the bitter and/or astringent substances which were volatile in baijiu,and a method for the extraction,separation,concentration,and identification of volatile bitter and/or astringent taste substances in baijiu was established.After taste verification with pure reference compounds,the bitter and/or astringent substances in baijiu were defined.Then,quantification of these bitter and/or astringent compounds,determination of taste thresholds,and calculation of their DoT,respectively.Finally,their contribution to the bitter and astringent taste of baijiu were founded.The main research content were as follows:（1）The baijiu was divided into volatile fraction and non-volatile fraction by vacuum rotary evaporation,it was found that the bitter and/or astringent taste in baijiu were volatile after the taste evaluation.The baijiu sample was separated into 4 fractions（A,B,C,and D）by gradient vacuum distillation.The fraction B with strong astringency and bitterness was re-separated by semi-preparative-HPLC,and 10 fractions were obtained.Each fraction was extracted by pentane and diethyl ether,and the diethyl ether extraction phase was collected.each organic phase was divided into two parts,the one for GC-MS was concentrated to 250μL under a gentle stream of nitrogen;the other was washed with pure water and water phase,removed the solvent by vacuum,and then for taste evaluation and taste dilution analysis（TDA）.（2）According to the results of TDA,The 4 fractions B-8-II,B-2-II,B-3-II,and B-4-II had high TD factors of 128,64,32,and 8 for astringency,and 32,16,16 and 8 for bitterness,respectively,and 7 taste-active compounds were identified by GC-MS.Based on the reference compounds,2-phenylethanol and ethyl·lactate contributed astringency only,while furfural,2-methypropanol,3-methybutanol,1-butanol,and 1-propanol gave both bitter and astringent taste.Among them,it was the first time to report the taste characteristics of 2-phenylethanol.Tyrosinol,acrolein,dimethyl disulfide,3-methylthio-1-propanol,and amino acids were presumed as bitter taste substancesin baijiu by former researchers,which were concluded that they were not the bitter substances in baijiu.（3）The recognition threshold concentrations were determined in bottled water（pH 3.8）by means of a triangle test for bitterness and the half-tongue test for astringency.The 7 astringent compounds showed much lower recognition threshold concentrations ranging from 2.259×10-3 to 4.713 mmol·L-1,among them,2-phenylethanol showed the lowest threshold,followed by furfural,then 2-methy-1-propanol,1-butanol,and 3-methy-1-butanol,n-propanol and ethyl·Lactate had higher astringency thresholds.The 5 bitter taste compounds with recognition threshold concentrations were ranged between 0.782 and 31.46 mmol·L-1,among them,furfural had the lowest threshold concentration,and n-propanol had the highest,followed by 1-butanol,2-methy-1-propanol,3-methy-1-butanol.（4）7 kinds of bitter and/or astringent compounds in baijiu were quantified by GC-MS and GC-FID,and the contribution of each bitter and/or astringent compound to the bitter and astringent taste of baijiu was evaluated by calculating DoT.For astringency,all of the DoT of the 7 astringent compounds were more than 1,which indicated that all compounds showed astringent taste in baijiu.For bitterness,the DoT of furfural in all types baijiu were greater than1,except for the chixiang aroma type baijiu,which was an important bitter compound in baijiu.The DoT of 2-methy-1-propanol and 3-methy-1-butanol in qingxiang,rice,fengxiang,sesame-like,and medicinal aroma types baijiu were>1,which contributed bitter taste in these types of baijiu.（5）At the conditions of pH 3.0,3.8,and 5.0,the effects of common organic acids such as lactic acid,acetic acid,and hexanoic acid on the bitterness and astringency of 3-methy-1-butanol were investigated.It was found that organic acids had no effect on the bitter taste of 3-methy-1-butanol,but it had an effect on the astringency,at the same conditions of pH,the effect was ranked as acetic acid>lactic acid>hexanoic acid. |
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