Causes And Improvement Measures Of Bitterness Of Maotai-Flavor Baijiu

Bitterness is the most common off-flavor that affects the style of Maotai-flavor Baijiu and the sensory quality.In this project,by analyzing the UV absorbance value and volatile substances of of Maotai-flavor Baijiu,determinetasting threshold of bitter substances,calculating the Doseover-Threshold（Do T）value of Renhuai Maotai-flavor Baijiu,and simulating the fermentation of Baijiu,the contribution of bitter presenting substances to the bitterness of Baijiu were determined,the influence of common organic acids and organic esters in Maotai-flavor Baijiu on the presentation of bitter substances were explored,the relationship between the bitterness of the Maotai-flavor Baijiu and the content of ethyl acetate divided by the content of isoamyl alcohol were examined;the production process of ethyl acetate and isoamyl alcohol were optimized.The main research contents are as follows:Principal component analysis（PCA）is used to study the discrepancy between UV absorbance values and volatile compounds of different origins and batchs of Maotai-flavor Baijiu,and partial least squares discriminant analysis（PLS-DA）is used to quantify and identify potential marked volatile compounds.For the UV absorbance value,the Beidacang Baijiu is better separated from the Jinsha Maotai-flavor Baijiu and Renhuai Maotai-flavor Baijiu.The 3rd,4th and 7th batches of Jinsha Maotai-flavor Baijiu,the 4th,5th and 6th batches of Renhuai and Maotai-flavor finished Baijiu are related.For volatile ingredients,PCA can be used to distinguish Jinsha and Renhuai Maotai-flavor Baijiu from Beidacang Maotai-flavor Baijiu.In the PLS-DA model of 53 volatile compounds,five volatile compounds of acetic acid,propionic acid,n-butyric acid,1,2-propanediol and 2-methyl-1-butanol were identified as potential labeling compounds based on the variable importance in projection values（VIP）（>1.5）.Hierarchical clustering analysis can cluster Jinsha and Renhuai Maotai-flavor Baijiu and distinguish them from Beidacang Maotai-flavor Baijiu.For the determination of bitter substances by ten samples test（TST）and best estimate threshold（BET）,the threshold of n-butanol is the lowest at 32.967 mg·L^-1,and the highest bitterness threshold is isobutyl alcohol,which is 233.253 mg·L^-1.According on the average concentration of the ingredients of Renhuai Maotai-flavor different batches Baijiu,the degree of bitterness is obtained:isoamyl alcohol>furfural>isobutanol>n-propanol>n-butanol,and the contribution of substances to the bitterness of Maotai-flavor Baijiu shows an additive effect;the shielding effect of acid and esters on bitterness is:ethyl acetate>acetate acid>ethyl lactate>lactic acid,and the masking effect of esters on bitterness is multiplicative.The bitterness of Maotai-flavor Baijiu showes an upward trend with the increase of the batches,among which the bitterness of different batches of Beidacang Maotai-flavor Baijiu is negatively correlated with the content of isoamyl alcohol divided by the content of ethyl acetate,while the bitterness of Jinsha and Renhuai different batches Maotai-flavor Baijiu is positively correlated with the content of isoamyl alcohol divided by the content of ethyl acetate.On the basis of the one-factor test,the Box-Behnken design experiment is carried out by selecting pH,Aspergillus oryzae inoculation（%）,and yeast inoculation（%）.The highest ethyl acetate content and the largest ratio of ethyl acetate to isoamyl alcohol content is determined.After optimizing the process,the pH is 6,the inoculation amount of Aspergillus oryzae（%）is 1,and the yeast inoculation（%）is 1.The content of ethyl acetate in the fermentation broth is determined to be 5067.73 mg·L^-1,ethyl acetate content/isoamyl alcohol content of 56.55.The relative errors with the predicted values are 5.89%and 13.37%,respectively.the error is small.To high-temperature Daqu,Saccharomyces cerevisiae（inoculum 1%）,and Wickerhamomyces anomalus（inoculum 1%）are added to Aspergillus oryzae（inoculum 1%）for 5 days of liquid fermentation.The content of ethyl acetate produced by the fermentation increased 2.6 times after the addition of Aspergillus oryzae,and the content of isoamyl alcohol did not change significantly.