Study On Microbial Fluctuation And Substance Change During Accumulation Of Spring-flavor Baijiu

Spring-flavor Baijiu,an emerging innovative liquor that integrates the essence of sesame-flavored liquor technology and strong-aroma liquor technology,has undergone over a decade of research and development.The high-temperature stacking process is an indispensable stage in its brewing process and production.This thesis investigates the sensory and physicochemical conditions,microbial community structure,and flavor compounds during the high-temperature accumulation process of Spring-flavor Baijiu.The study aims to understand the growth and decline of microorganisms and the changes in material composition that occur during the accumulation process of Spring-flavor Baijiu.These findings provide a data-based explanation and theoretical basis for analyzing the brewing mechanism of the liquor.The primary results are as follows:(1)This study tracked the sensory,physical,and chemical properties of the liquor at various stacking times during the production of Spring-flavor Baijiu.The results revealed significant changes in the sensory perceptions of the liquor mash during the stacking process,which provide valuable insights into the growth and decline of microorganisms and material changes that occur during the accumulation process.This study outlines the optimal ranges for several physical and chemical indexes during the high-temperature accumulation of Spring-flavor Baijiu.These are:starting temperature(25℃-27℃),stacking temperature(52℃-55℃),moisture(45%-52%),acidity(2.2 mol/10g-3.0 mol/10 g,typically within 2.5mol/10 g during stacking),reducing sugar(3%-5%),and starch(18%-25%).The accumulation process involves minimal alcohol production and has a short duration,hence no particular range is required for the alcohol content.The high-temperature accumulation stage is characterized by an increase in temperature,gradual decomposition of starch,accumulation of reducing sugar,slight increase in alcohol concentration,and change in water acidity.This stage can be observed simultaneously with the aforementioned low-temperature enzymatic hydrolysis phase.(2)Using high-throughput sequencing,we investigated the microbial growth and community structure of Spring-flavor Baijiu during different stacking times.Our results reveal that bacterial richness and diversity were significantly higher than those of fungi,with a ratio of approximately 5:1.These findings suggest that bacteria are the dominant microorganisms in the stacked liquor of Baijiu.During the high temperature accumulation process,the microbial taxa decreases,resulting in the simplification of the community structure.Meanwhile,the relative abundance and biomass of microorganisms also increase.The high-temperature accumulation stage facilitates the accumulation and unification of microorganisms,thereby providing a source of bacteria and various precursors for the subsequent fermentation of wine mash.The stacked wine brew samples were found to harbor a total of 36 orders,301 genera,and440 species of bacteria,alongside 13 orders,73 genera,and 99 species of fungi.The dominant genera were Bacillus and Wickham yeast,respectively.Moreover,we analyzed the structural composition and change of the core microbial community at each accumulation time point.(3)The headspace solid phase microextraction gas chromatography-mass spectrometry method for detecting volatile flavor substances during high-temperature accumulation was optimized.The ideal extraction parameters are: 7.5 % sample extract(ethanol)concentration,6 liquid-material ratio,17.5 minute extraction time,and 52 ℃extraction temperature.A total of 106 volatile flavor compounds were detected in wines with different aging periods.Of these,38 were esters,followed by 17 alcohols,16 aldehydes and ketones,7 acids,and 30 other aroma components,highlighting the significance of esters,alcohols,and aldehydes and ketones as primary volatile compounds in high-temperature aged Spring-flavor Baijiu.We regularly analyzed and summarized the relative content of major volatile aroma components in wine subjected to high-temperature accumulation at different stacking times.The results indicate that the early accumulation stage had lower amounts of alcohol and ester compounds but had a higher concentration of acid compounds,aldehydes,and ketones.The relative concentration of alcohols and esters increase significantly towards the end of the accumulation,while the content of acids,aldehydes,and ketones decrease.These results confirm that high-temperature accumulation fermentation in Spring-flavor Baijiu is a stage of both microbial enrichment and growth,leading to the production of baijiu aroma substances and various precursor substances.This mechanism provides a material foundation for fermentation in the pool.This study elaborated systematically and comprehensively on the high-temperature accumulation process of Spring-flavor Baijiu by exploring three different aspects.These findings provide theoretical guidance for optimizing the high-temperature accumulation process of Spring-flavor Baijiu and achieving comprehensive mechanization and automation during fermentation.