| Medium-high temperature Daqu is a significant source of aroma compounds and precursors in Baijiu production.As a saccharifying and fermenting agent,it contributes to both the quality and yield of Baijiu.Aroma is a crucial factor in evaluating the quality of medium-high temperature Daqu.Currently,the evaluation of Daqu aroma relies on sensory methods,which are subjective and difficult to quantify.To address this issue and scientifically evaluate the aroma quality of medium-high temperature Daqu,this study employed headspace solid-phase microextraction combined with gas chromatography-mass spectrometry to analyze Daqu samples.Principal component analysis and gas chromatography-sniffing were used in conjunction with relative odor activity to identify key flavor components that significantly contribute to Daqu aroma.An evaluation model for medium-high temperature Daqu aroma quality was established.The main research contents are as follows:Using the headspace microextraction method,optimal extraction conditions were determined.A 50/30 μm DVB/CAR/PDMS solid-phase microextraction head was used to extract Daqu aroma.The sample weight was 0.5 g,the extraction time was 52 min,the equilibration time was 21 min,the extraction temperature was 61℃,and the resolution time was 5 min.This study developed a method for determining volatile flavor components in medium-high temperature Daqu that requires low sample usage,has simple pretreatment,and exhibits high accuracy and good reproducibility.Using this method,a total of 101 volatile flavor components were detected from the samples using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry.These components included nine categories:esters,aromatics,aldehydes and ketones,pyrazines,alcohols,phenols,and heterocyclic compounds.Ester compounds had the highest content and variety of aroma substances in medium-high temperature Daqu,followed by aldehydes and ketones,pyrazines,and aromatics.The volatile flavor substances detected were analyzed by principal component analysis,GC-O method and relative odor activity value method,and finally 20 aromaactive compounds were identified as the main aroma substances of medium-high temperature Daqu.Of these,eight key aroma substances contributed most to the overall flavor.These were ethyl hexanoate,(E)-nonenal,hexanal,nonanal,ethyl heptanoate,phenylethylaldehyde,decanal and phenylethanol.Ethyl caproate had the highest aroma activity value and contributed most to the aroma of medium-high temperature Daqu.Building on these findings,an aroma quality evaluation model was constructed using principal component analysis and the 20 main aroma substances of medium-high temperature Daqu as evaluation indices.Two principal components were extracted,resulting in the model expression F=0.933 × F1+0.067 × F2.This model can be used to visually evaluate the aroma quality of 11 currants,and its evaluation results are consistent with sensory evaluation and cluster analysis results.Three blind samples were selected to validate this model,and the model evaluation was consistent with sensory evaluation results.This model offers a more objective method for evaluating Daqu aroma than traditional sensory evaluation,improves the Daqu quality evaluation system,and supports the intelligent and digital transformation of the traditional brewing industry. |
