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Strategies For Reduction Of Isoamyl Alcohol And Control Its Synthesis During Strong Aroma Baijiu Fermentation

Posted on:2023-06-14Degree:MasterType:Thesis
Country:ChinaCandidate:Q W LiangFull Text:PDF
GTID:2531306818997929Subject:Microbiology
Abstract/Summary:PDF Full Text Request
Higher alcohols are flavor substances in baijiu.They may bring discomfort upon drinking when present at the high level in baijiu.Optimizing the fermentation process is one of the effective measures to control the content of isoamyl alcohol within an appropriate range.Thus,it is of great significance to investigate the influence of fermentation conditions on the synthesis of isoamyl alcohol in the fermentation process of baijiu for precisely control of it.In this work,the relationship between fermentation conditions(species and initial concentration of yeast,the initial fermentation temperature,enzyme activity of Qu)and the level of yeast proliferation,reducing sugar consumption and isoamyl alcohol synthesis in the fermentation process of strong aroma baijiu were systematically studied.Moreover,the effects of collaborative fermentation using microorganisms on the synthesis of isoamyl alcohol were investigated.The results lay a theoretical foundation for elucidating the regulatory mechanism of isoamyl alcohol synthesis during baijiu fermentation and development of techniques for reduction and control of isoamyl alcohol.The main results are as follows:(1)It was revealed that the proliferation factor and reducing sugar consumption rate of Saccharomyces cerevisiae are the key factors affecting the synthesis of isoamyl alcohol in the fermentation process of strong aroma baijiu.The multiplication folds of Saccharomyces cerevisiae and the estimated apparent sugar consumption rate were found to be the key factors affecting the synthesis of isoamyl alcohol during fermentation.By increasing the initial concentration of Saccharomyces cerevisiae,the estimated apparent sugar consumption rate can be significantly reduced and the synthesis of isoamyl alcohol was reduced by 22.9%.The species and initial concentration of Pichia had no significant effect on the estimated apparent rate of sugar consumption,neither did it shown the possibility to reduce synthesis of isoamyl alcohol during fermentation.(2)Investigation of the effects of fermentation conditions on the synthesis of isoamyl alcohol.An appropriate decreasing the initial fermentation temperature can reduce the estimated apparent reducing sugar consumption rate at the early stage and significantly reduce the synthesis of isoamyl alcohol.The multiplication fold of Saccharomyces cerevisiae,estimated apparent reducing sugar consumption rate and isoamyl alcohol synthesis at 18°C were 0.6 orders of magnitude,59.5%and 22.6%lower than those at 26°C,respectively.Alteration of the oxygen content in fermented grains by adjusting the loading amount,did not show significant differences in yeast multiplication folds and reducing sugar consumption rate.And the synthesis of isoamyl alcohol was not decreased.(3)Reduction of synthesis of isoamyl alcohol during baijiu fermentation by adjusting enzymatic activity of Qu.Using Daqu with low saccharifying enzyme activity(228.5–306.1U·g-1)for fermentation,the estimated apparent sugar consumption rate and isoamyl alcohol content were reduced by 34.8–40.3%and 10.3–13.3%,respectively.Addition of bacterial Fuqu to semi-solid fermentation systems and solid fermentation systems can reduce the synthesis of isoamyl alcohol by 30.0%and 13.3%,respectively.However,using Fuqu prepared by Aspergillus oryzae or protease for fermentation,both the multiplication fold of S.cerevisiae and the estimated apparent reducing sugar consumption rate increased.This caused the increasing content of isoamyl alcohol by 24.7%and 14.0%,respectively.(4)Reduction of the synthesis of isoamyl alcohol by microbial collaborative fermentation.The employment of Wickerhamomyces anomalus 2B4 with high ethyl esterase activity for the semi-solid fermentation of baijiu,isoamyl alcohol was decreased by 48.8%with a 47.4%increasing for isoamyl acetate.This yeast strain was also employed in a solid-state fermentation system,the synthesis of isoamyl alcohol was reduced by 3.9%compared with the control.Synthesis of isoamyl alcohol was not decreased when Weissella or Clostridium was used in the solid-state fermentation system under anaerobic conditions.
Keywords/Search Tags:isoamyl alcohol, strong aroma baijiu, Saccharomyces cerevisiae, apparent sugar consumption rate, enzymatic activity of Daqu
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