Study On The Key Indicators Screening And Quality Evaluation Method Of Shaoxing Huangjiu Wheat Qu

Wheat Qu,an important raw material for the production of Huangjiu,has a very important influence on the fermentation and flavor formation of Huangjiu.Wheat Qu is produced by solid state fermentation process with an open environment,which means the environmental factors are complex and its quality is difficult to control.At present,the quality evaluation of wheat Qu mainly adopts simple sensory evaluation,and the quality evaluation method of wheat Qu has not been established.It is still unclear how wheat Qu affects the fermentation and flavor formation of Huangjiu.In this study,Shaoxing Huangjiu wheat Qu was used as the research object,and the influence of wheat Qu quality on the fermentation and flavor formation of Huangjiu were analyzed on the basis of comparing the quality and properties of wheat Qu,and then important indicators and key indicators for evaluating wheat Qu quality were screened out through correlation analysis.In the end,the quality evaluation method of Shaoxing Huangjiu wheat Qu was established,and the influence of wheat Qu quality on the fermentation process of Huangjiu was further discussed.The main results of this paper were as follows:1.The sensory indicators,physical and chemical indicators,flavor substances and microbial community structures of 12 wheat Qu samples were analyzed.The sensory evaluation determined that A4,B4,C1 and C3 were superior grade wheat Qu.Compared with common wheat Qu,their liquefying power(2.98~3.24 U/g),saccharifying power(1558.13~1713.45 U/g),acid protease activity(38.17~54.97 U/g),liquor-producing power(10.77% vol~12.22% vol),total free amino acid content(184.58~470.70 mg/100g),Bacillus(55.76%~82.41%),Issatchenkia(10.11%~21.12%)and Aspergillus(7.97%~11.01%)were significantly higher,while Saccharomyces(8.15%~12.63%)and Staphylococcus(0.37%~2.11%)were significantly lower.2.Through the experiment of Huangjiu fermentation,the influence of wheat Qu quality on the fermentation and flavor formation of Huangjiu were analyzed.The results of sensory indicators showed that the wine of Huangjiu produced by superior grade wheat Qu were bright,full of aroma,fresh and mellow,and harmonious in style.The taste of wheat,nutty,smoky and fruit aroma of Huangjiu produced by superior grade wheat Qu were more outstanding.The results of physical and chemical indicators showed that the alcohol content(13.20%vol ~15.50%vol)and amino acid nitrogen(0.61~0.94 g/L)of Huangjiu produced by superior grade wheat Qu were significantly higher than the alcohol content(8.80%vol ~12.00%vol)and amino acid nitrogen(0.38~0.58 g/L)of Huangjiu produced by common wheat Qu.The results of flavor indicators showed that the total content of organic acids(12.29~14.72 g/L),free amino acids(3.30~5.51 g/L)and volatile aroma substances(10.24~10.91 mg/L)of Huangjiu produced by superior grade wheat Qu were significantly higher than the total content of organic acids(8.54~10.82 g/L),free amino acids(1.93~3.62 g/L)and volatile aroma substances(6.72~8.66 mg/L)of Huangjiu produced by common wheat Qu.3.Through the establishment of partial least squares regression model,the correlation between the wheat Qu indicators and the Huangjiu indicators was analyzed,and 13 important indicators for evaluating wheat Qu quality were screened out,including 4 physical and chemical indicators(liquefying power,saccharifying power,acid protease activity,liquor-producing power),3 flavors indicators(tartaric acid,sweet amino acids,alcoholic substance),6 microbial indicators(Staphylococcus,Saccharopolyspora,Bacillus,Kroppenstedtia,Issatchenkia,Aspergillus).Principal component analysis of wheat Qu samples was carried out by using these 13 indicators,and it was found that the superior grade wheat Qu and common wheat Qu could be well distinguished.4.The PLSR models were established between the 13 wheat Qu indicators and the sensory scores of wheat Qu.Three key indicators for evaluating wheat Qu quality were screened out,including liquefying power,acid protease activity and Aspergillus abundance.Then 3 wheat Qu samples were re-selected for verification.The results showed that the wheat Qu with high value of key indicators had higher sensory scores and better quality of Huangjiu.In the end,3 key indicators were used as the first class indicators,and the remaining 10 important indicators were used as the second class indicators to establish the quality evaluation method of Shaoxing Huangjiu wheat Qu.5.Through tracking the physical and chemical changes in the fermentation process of Huangjiu,the influence of wheat Qu quality on the fermentation process of Huangjiu were further analyzed.The results showed that the pre-fermentation process of Huangjiu using superior grade wheat Qu accorded with the rule of pre-slow,medium-station,and slow-down,and its fermentation started faster,and its fermentation strength was stronger,while the prefermentation process of Huangjiu using common wheat Qu was more moderate,and its fermentation started slower.In addition,the rate of reducing sugar consumption,alcohol production,total acid production and amino acid production were faster in the Huangjiu fermentation process using superior grade wheat Qu.