Bound Aroma Compounds Of Liquor-making And Qu-making Materials

Chinese liquor is a traditional Chinese distilled liquor made from cereals,processed by cooking,saccharification,fermentation,distillation,storage and blending.Bound aromas are volatile flavor components released by flavorless flavor precursors in the role of acid or enzyme.The raw materials’ bound aromas are a potential factor affecting the quality of Chinese liquor.In the process of qu-making,fermenting,distilling etc,flavor precursors decompose and release free aroma compunds,which will become a part of Chinese liquor’s flavor.Over years,most of the research has focused on raw materials’ ingredients such as starch,protein etc and brewing characteristics,while little attention has been paid to bound aromas.Therefore,the purpose of the research was to fully understand bound aromas by different means of hydrolysis and to explore the composition of flavor precursors according to the detected compounds so as to provide a basis for the study of raw materials on the contribution of Chinese liquor’s flavor.What’s more,the existence of β-glucosidase in Daqu and fermented grains and the hydrolysis effect of crude enzyme solution on flavor precursors were preliminary explored in order to lay the foundation for the study of the property of β-glucosidase and flavor hydrolysis mechanism.The main contents of the research were as follows:（1）The SPE column was used to adsorb flavor precursors,and then,which were hydrolyzed by acid to release volatile compounds.The HS-SPME coupled with GC-MS was employed to study bound aromas of raw materials（sorghum,wheat,pea,corn and wheat bran）.55 kinds of aroma compounds were detected in raw materials,including 10 alcohols,11 aldehydes,6 ketones,11 aromatic compounds,15 terpenoids and 2 furans.Among them,42 compounds were first detected in raw materials’ bound aromas.（2）To fully understand the composition of bound aromas in raw materials,the SPE column was employed to adsorb flavor precursors,and then,which were hydrolyzed by β-glucosidase to release volatile compounds.The HS-SPME coupled with GC-MS was used to study bound aromas of raw materials.54 kinds of aroma compounds were detected,including 11 alcohols,6 aldehydes,10 ketones,7 aromatic compounds,5 terpenoids,4 acids,8 esters,1 sulfide and 2 heterocyclic compounds.The compounds by two kinds of hydrolysis methods were quite different.40 kinds of free aroma compounds were detected,including 12 alcohols,5 aldehydes and ketones,6 aromatic compounds,10 acids,5 esters and 2 furans.Compared with bound aromas,there were large differences in compound types.40 compounds were only detected in bound aromas.（3）The bis（trimethylsilyl）trifluoroacetamide（BSTFA）coupled with GC-MS was employed to establish an indirect detection method of glycosides.The concentration of glycosides in raw materials（sorghum,wheat,pea,corn,barley,rice,glutinous rice and wheat bran）ranged 26.45⁵376 mg kg^-1.Besides,3 kinds of precursors were first identified,respectively phenyl-β-D-glucopyranoside,2-phenylethyl-β-D-glucopyranoside and 2-phenylethyl-α-L-rhamnose-β-D-glucopyranoside.Phenyl-β-D-glucopyranoside and 2-phenylethyl-α-L-rhamnose-β-D-glucopyranoside were identified temporarily.2-phenylethyl-β-D-glucopyranoside and 2-phenylethyl-α-L-rhamnose-β-D-glucopyranoside were the precursors of 2-phenethyl alcohol,phenyl-β-D-glucopyranoside was the precursor of benzyl alcohol.（4）β-glycosidase existed in Daqu and fermented grains,which hydrolyzed flavor precursors in raw materials to produce volatile flavor compounds during fermentation.