Sensory-Guided Analysis Of Retronasal Burnt Aroma And Less-Volatile Bitter Taste Compounds In Soy Sauce Aroma Type Baijiu

Flavor is one of the most important characteristics of foods,it greatly affects the choice of consumers.To analyze the mystery of flavor is always a key scientific issue of foods,and to analyze the chemical natural of flavor is a basis of food flavor research.Chinese Baijiu has a very complex flavor profile.Previous studies about the flavor compounds of Baijiu were mainly focused on the orthonasal aroma compounds,whereas the studies on the retronasal aroma and taste compounds are nearly blank.However,these flavor compounds also have an important contribution on the overall flavor of Baijiu.This study focused on the retronasal burnt aroma and less-volatile bitter taste compounds in soy sauce aroma type Baijiu,and used the modern flavor analysis approach to analyze the flavor compounds.The main contents were as followed:(1)Based on the Sensomics strategy,this study developed a sensory-guided fractionation method to analyze the retronasal aroma compounds in Baijiu.By using the sensory-guided fractionation,two target fractions 2-II-7 and 2-II-10 were screened from the Baijiu sample.For fraction 2-II-7 with relative simple chemical compositions,target compound 2-1 was screened using the two-step HPLC separation.This compound was enriched and purified by gel chromatography and HPLC in turn,and identified by HRMS and 1D/2D NMR as 6-(2-formyl-5-methyl-1H-pyrrol-1-yl)hexanoic acid.(2)Based on the Flavoromics strategy,this study combined Sensomics and Flavoromics to identify the flavor compounds in complex food matrix.For fraction 2-II-10 with complex chemical compositions,target compound 3-1 was screened by combining multivariate data analysis(PLS)and sensory-guided fractionation.This compound was identified by using HRMS and chemical synthesis.Sensory evaluation revealed that the aroma threshold of compounds 2-1 and 3-1 in 53% ethanol aqueous solution were 209.5 and 515.0 ?g/L,respectively.On the basis of the dose-overthreshold factor and addition experiment,compound 3-1 was confirmed as a key contributor to the retronasal burnt aroma of soy sauce Baijiu.Moreover,the sensory evaluation also revealed that compound 2-1 may contribute to the retronasal burnt aroma of the Baijiu at its subthreshold concentration by the additive effect with compound 3-1.(3)By applying taste dilution analysis,the less-volatile bitter taste compounds were identified as(E)-9,12,13-trihydroxyoctadec-10-enoic acid and(E)-9,10,13-trihydroxyoctadec-11-enoic acid in soy sauce Baijiu.The two compounds were the oxidation products of linoleic acid(LA),and it was suggested that LA metabolism is the main source of trihydroxy octadecenoic acid,and there should be other LA oxidation products in Baijiu.(4)The HRMS combined with NMR for the first time identified 12 LA oxidation products(include the two trihydroxy octadecenoic acids identified above)in typical soy sauce,strong,and light aroma type Baijiu samples.The discovery enhanced acknowledge of lipid oxidation products in Baijiu.Moreover,a quantitative method was built with UPLC-MS and the concentrations of these compounds were analyzed.Since some of the LA oxidation products usually had a negative effect on the food quality,their concentrations in Baijiu should be monitored and controlled.The quantitative approach developed in the study could simultaneously detect the 12 LA oxidation products which are common in Baijiu,the approach showed a good accuracy,precision,and recovery,which might provide a reference for the detection of LA oxidation products in other Baijiu samples.