Screening And Application Research Of Functional Bacteria Producing Ferulic Acid During The Brewing Process Of Sesame-Flavor Baijiu

Sesame-flavored baijiu is a typical example of Lu jiu,which is mainly made from sorghum and wheat.The high-temperature daqu and fuqu made from bran are used as saccharification fermentation starter.Ferulic acid,due to its strong antioxidant properties,has been proven effective against various diseases such as skin diseases,cancer,cardiovascular and cerebrovascular diseases,and obesity.Ferulic acid is also an important precursor substance that can be used to synthesize high value-added compounds like 4-vinylguaiacol(4-VG)and vanillin,which is a special volatile component with a clove-like aroma.In recent years,there has been an increasing number of studies on the application of ferulic acid as a functional factor for promoting health benefits in food and beverages.However,there has been limited research on ferulic acid in baijiu brewing.Therefore,studying the mechanism of ferulic acid production and transformation during the brewing of baijiu is crucial for the development of high-quality baijiu.This thesis explores the production and transformation of ferulic acid in Baotuquan sesame-flavoured baijiu,as well as the screening of high ferulic acid esterase functional strains,the preparation process of high ferulic acid esterase functional fuqu,and the effect of functional fuqu on the process brewing of baijiu.The goal is to reveal the mechanism of ferulic acid production and transformation,and provide a scientific basis for developing a sesame-flavoured baijiu brewing process that yields high levels of ferulic acid.(1)Ferulic acid and its high-value conversion product 4-VG were identified and quantified in Baotuquan sesame-flavoured baijiu using HPLC and GC-MS analysis.Ferulic acid production during the brewing of sesame-flavoured baijiu was investigated using the traditional Baotuquan brewing process as a model.The study revealed that the pre-stack fermentation and pre-solid fermentation stages are crucial for ferulic acid production.Moreover,the presence of metabolically active functional microorganisms that secrete ferulic acid esterase during the stacking stage can be utilized to identify ferulic acid esterase-producing microorganisms.(2)Baotuquan sesame-flavored baijiu stacked fermentation grains were used as the screening material to obtain 89 strains with ferulic acid esterase activity.Fuqu solid fermentation re-screening resulted in the identification of two best enzyme-producing strains,which were identified using molecular biology as Enterobacter hormaechei BZE-5(hereinafter referred to as BZE-5)and Pseudomonas oryzihabitans BZE-72.The study of the biological characteristics of the two bacterial strains revealed that BZE-5can withstand high temperatures,high sugar,high ethanol,high acid,and high salt environments.Furthermore,BZE-5 can grow normally during the high-temperature accumulation of sesame-flavored baijiu.(3)The Baotuquan bacterial fuqu medium was used as the initial medium to optimize the preparation process of BZE-5 functional fuqu through single-factor,PB test,and BBD response surface optimization.The best preparation process of BZE-5functional fuqu was determined to be rice hull addition of 5.7%(w/w),initial water content of 1:1(w/w),Na OH amount of 2.2g/kg,and incubation time of 74 hours.Under these conditions,three parallel validation tests were conducted,and the actual value of ferulic acid esterase enzyme activity in fuqu was found to be 1549.35±22.12 m U/g Dw.The error value was 2.46% from the predicted value of 1587.39 m U/g Dw.The enzyme activity of the functional fuqu was approximately 2.11 times higher than the original enzyme activity.(4)The study aimed to investigate the effect of adding BZE-5 functional fuqu on the natural fermentation of sesame-flavored baijiu and the quality of the fresh baijiu by monitoring key physicochemical indices,the evolution of the number of brewing microorganisms,changes in flavor substances,and sensory evaluation during the brewing process of Baotuquan sesame-flavored baijiu.The results showed that the addition of functional fuqu did not significantly affect the natural fermentation of baijiu.However,the content of ferulic acid in the fermented grains and fresh baijiu from the test group decreased after the addition of functional fuqu,while the content of4-vinylguaiacol increased significantly.This indicated that the functional bacterium BZE-5 had two different abilities in the complex brewing microbiological system.It had a strong ability to produce ferulic acid in the early stage(0-15 d)of stack fermentation and solid-state fermentation,but the ability to produce 4-vinylguaiacol in the middle and late stage(20-60 d)of solid-state fermentation.