| The Yellow Crane Tower light-flavor Baijiu is brewed near the Han River,known as the "South Tower and North Fen".At present,researches on the main characteristic flavor substances within it,the types of yeast contained in the microbial community and their physiological characteristics have not been studied in depth.This study intended to analyze the flavor or functional substance components within the wine base,and explored the source of the substance,and then isolated the core yeast strains involved in the fermentation process,and clarified the physiological and biochemical characteristics of each strain.The thesis aimed to provides an important scientific theoretic basis for in-depth exploration of the role played by the core yeast in the fermentation system,and also to provide an important technical support for the technology improvement.The HS-SPME-GC-MS analysis technology was used to quantitatively analyze the composition of Yellow Crane Tower light-flavor Baijiu.A total of 72 volatile substances were detected and analyzed,including 17 alcohol compounds,28 ester compounds,and aldehyde compounds.7 kinds,3 kinds of ketone compounds,9 kinds of fatty acid compounds,2 kinds of pyrazine compounds,2 kinds of furan compounds,16 kinds of aromatic and phenolic compounds.In terms of flavor substances,the content scopes of ethyl lactate and ethyl acetate,which are the two main substances included in the lightflavor Baijiu,were 2 g/m L?3 g/m L and 1 g/m L?2 g/m L,respectively and the overall content of which in the first round of fermentation Baijiu was higher than that of which in the second round of fermentation Baijiu.The content of furfuryl alcohol was high,up to 1087.50 mg/L in the first round of fermentation Baijiu and 3856.72 mg/L in the second round of fermentation Baijiu.The ratio of isoamyl alcohol to isobutanol is 1.68 in the second round of fermentation Baijiu and 1.78 in the second round of fermentation Baijiu.In terms of healthy substances,the content of guaiacol is 9.33 mg/L,which is higher than the reported value of 805.84 ?g/L.In addition,?-caryophyllene,exhibiting a variety of physiological activities was found in the second round of fermentation Baijiu,and its content reached 210.25 ?g/L,but it didn't exist in the first round of fermentation Baijiu.In order to explore the source of the substances in the wine,50 compounds were detected from Daqu,which could be found in the first round of fermentation Baijiu.Therefore,not all the substances in the wine base were derived from Daqu,so some were related to the natural fermentation process in the local factory.In order to explore the dynamic changes in the fermentation process,different Jiupei fermented at the 0 d,3 d,7 d,14 d,21 d,28 d were collected,and the physical and chemical properties,such as moisture content and sugar content,were tested.And also,the content of organic acids,ethanol,ethyl acetate,n-propanol and other flavor substances were detectedto analyze their content changes in different time periods.The results showed that most of the substances were produced during the 3rd to 21 st days of fermentation,and stabilized or slightly decreased from 21 st to 28 th days.A total of 119 yeast strains were screened and isolated from the Daqu and Jiupei of Yellow Crane Tower's light-flavor Baijiu by adopting WL medium.The 26 S r RNA D1/D2 region of the 119 yeast strains was amplified by PCR technology.After sequencing,the comparison and analysis were performed.All the 119 yeast strains can be classified into 5 types of yeasts,including Saccharomyces cerevisiae,Issatchenkia orientalis,Wickerhamomyces anomalus,Saccharomycopsis fibuligera,and Candida humilis.The result of growth curve showed that 5 kinds of yeast enter logarithmic growth stage after 2 h.Wickerhamomyces anomalus usually grows the fastest and Issatchenkia orientalis grows the slowest.After 16 hours,the 5 strains enter the stable period.The experimental result of enzyme activity measurement showed that Saccharomycopsis fibuligera mainly played a role in saccharification and glucoamylase activity was 1870.30 U/m L,and Wickerhamomyces anomalus and Issatchenkia orientalis were mainly responsible for esterification,ethyl acetate and ethyl lactate content was 866.17 mg/L,688.60 mg/Lin Wickerhamomyces anomalus,599.04 mg/L and 220.26 mg/L in Issatchenkia orientalis.Candida humilis performed esterification and saccharification effects,and it had a strong ability to produce phenethyl alcohol.The productivity of tetramethylpyrazine of Candida humilis was higher than that of other 4 yeasts The contents of pyrazine and phenethyl alcohol were 7.748 mg/L and186.00 mg/L.And its ability to produce esters was average,but the productivity of npropanol was low(1.566 mg/L)In general,Candida humilis is an excellent yeast,so far,there have been no research reports on it,related to the brewing of light-flavor Baijiu.In the application experiment of strengthening strains,the C.humilis HHLCH1 was mixed with low-temperature Daqu at a ratio of 3%,6%,and 9%,and the fermentation was simulated for 28 days under the conditions of solid-state fermentation.Compared with the control group that only added low-temperature Daqu,the content of five substances including ethyl acetate,ethyl lactate,phenethyl alcohol,tetramethylpyrazine,and guaiacol increased greatly in the test group.The content of 5substances in group HHLCH1(3%)increased by 93.57%,94.65%,0%,4277.37%,and144.43%;the group HHLCH1(6%)increased by 59.80%,94.34%,122.98%,3354.54%,387.09%,respectively;the group HHLCH1(9%)content of 5 substances increased by77.65%,101.61%,135.24%,2398.63%,405.35%,respectively.This study systematically analyzed the content of common flavor substances such as ethyl acetate,ethyl lactate,isoamyl alcohol,and also detected functional factors such as guaiacol and caryophyllene.5 kinds of core yeasts in the fermentation system were also screened and revealed the production characteristics of each strain.These results laid the theoretical foundation and technical support for the in-depth development and research of Huanghelou light-flavor Baijiu. |
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