Research On The Quality,Microbial Diversity And Production Process Of Vinegar Koji In Chishui

As a saccharification and fermentation agent in the vinegar production process,vinegar koji is used to provide special nutrition and aroma components for vinegar.The quality of the vinegar koji directly affects the vinegar product rate and quality.But the quality of the vinegar koji is difficult to guarantee due to the influence of the environment and the condition of making.Therefore,this subject takes the vinegar koji of Chishui as the research object.The physicochemical indexes,aroma components and microorganisms of koji in different periods were compared.The quality of the dried vinegar was compared and the process of preparing the koji was optimized.The main conclusions are as follows:?1?The analysis of the physiochemical indexes of vinegar koji in the three periods showed that the koji in May was better than the other two months,and it had a strong composite flavor and a good growth condition.The water content of the vinegar koji samples in the three periods all met the standard of mature vinegar koji.The acidity of the May song was the highest at 1.15 mmol/10 g.The acidity was mainly formed by the metabolism of organic acids by the acid-producing microorganisms and the degradation of fats,starches and proteins.The starch content in the three periods was significantly different?P<0.05?.The May koji had the lowest starch content of 46.55 g/100 g,indicating that it had a good growth.The liquefaction and glucoamylase activities of May was the highest,which was 2.60 U/g and 216.20 U/g respectively.It was with significant differences?P<0.05?.The May fermentation had the highest fermentation power and had a significant difference?P<0.05?,which was 0.62 g/?0.5g·72h?,indicating that the role in the later fermentation process was even greater.Comprehensive analysis of physical and chemical indicators,the May koji's best quality.?2?The determination about the number of microorganisms in the vinegar koji showed that the total number of bacterial colonies in May vinegar koji was higher than that in the other two months.The number of molds was significantly higher,which was2.6×10⁵ cfu/mL,and the growth of molds reflected the level of liquefaction enzymes and glucoamylase activity.In May,the number of lactic acid bacteria was the lowest,which was 8.5×10² cfu/mL.But the number of yeasts was high,which was 2.1×10⁴cfu/mL.This may be related to the culture environment,and it indicates the difference of microbial flora of vinegar koji.?3?The aroma components were tested.The results showed that the contents of esters in the aroma components in May and June were 31.92%and 31.50%,respectively,which were higher than those in April.They provided special aroma components for the koji.The contents of alcohols were 15.54%and 17.05%,respectively,which were lower than those in April.The levels of acids,aldehydes and ketones were similar,being13.96%¹6.67%and 1.47%³.14%,respectively.The main aroma components in the vinegar koji were determined by relative aroma activity method?ROAV?as follows:ethyl acetate,ethyl phthalate,linalool,1-ene-3-octanol,alpha-terpineol,Furfural,lauric aldehyde.?4?High-throughput sequencing was used to analyze the fungal and bacterial diversity of the vinegar koji samples.The results showed that the number of OTUs in the May koji sample was the highest,which was 652,indicating that sequencing information was more comprehensive.Alpha index diversity calculation results:The Shannon index of the May koji was the highest,which was 1.97,and the Simpson index was the lowest,which was 0.25.These indicated that the colony had a higher degree of richness.May koji detected the most abundant genus.Bacterial colony determination,the number of OTUs in the May koji sample was 3013,higher than the June koji sample,and lower than the number of OTU samples in the April koji.It indicated that the bacterial information in May koji was more comprehensive than the June koji,but lower than April.The Shannon index of the May koji sample was lower than that of the June koji.It was lowest in the April koji sample,which was 2.50.The Simpson index in May koji sample was higher than the June koji,and the April koji sample was the highest,which was 0.32.That indicated that the bacterial community diversity of the May koji was lower than June koji,but higher than April koji.The May koji has the highest bacterial genus.Based on the analysis of the diversity of fungi and bacterial colonies,May is more conducive to the growth of microorganisms in vinegar koji.?5?The results of sensory evaluation of sun-dried vinegar for the three periods showed that sun-dried vinegar was the best in May.The results of physical and chemical indicators showed that the total acid content was the highest in June at 4.35g/100mL,which was the lowest in April,and the quality of April was also the worst.The main source of organic acids in vinegar was during koji and fermentation.Fermentation of microorganisms produces a small amount of raw materials.Reducing sugar determination results:The content was the lowest in April and the highest in May at2.04 g/100 ml,and there was a significant difference?P<0.05?,which has a lot to do with the quality of vinegar koji during the three periods.Absorbance and pH were measured in three different periods,which were 0.228-0.232 L/?g·cm?and 3.61-3.66respectively.Based on comprehensive sensory evaluation and sensory index analysis,the quality of sun-dried vinegar in May was the best.?6?The result of the determination of aroma components showed that the volatile components in May were the most,which was 39.Combined with the relative odor activity value method to analyze the contribution of volatile components,it was found that the main aroma components of sun-dried vinegar are 7?ROAV?1?:sec-butyl acetate,2-methylbutanal,furfural,furfural,?-ionone,D-Limonene,2,4,5-trimethylazole.?7?Combining single-factor test and orthogonal optimization test,the influence of various factors on the koji making process was determined.Through the test verification,the best koji preparation condition was A₁B₃C₃D₂:the amount of Chinese herbal powder added was 7.5%and the culture temperature was 28°C.The amount of water was 125%and the natural fermentation time was 25 days.The liquefaction enzyme activity obtained at this time was 2.41U/g,the acidity was 1.24 mmol/10 g,and the fermentation force is 0.65 g/?0.5g·72h?.