| Saccharomyces cerevisiae is the principal species for wine making and plays an important role in wine quality.At present,active dry yeast(ADY)imported from abroad is mostly used in domestic wine brewing and limited knowledge of indigenous S.cerevisiae for wine-making has been known in China.So far,few Chinese indigenous S.cerevisiae strains were applied to wine industry.However,there are few reports on the influence of indigenous yeast resources on wild yeast resources and on the competitive relationship between them.CECA yeast is an excellent indigenous S.cerevisiae strains screened from the eastern foot of Helan Mountain in Ningxia,it can give Cabernet Sauvignon wine a strong fruity smell.In order to promote the popularization and application of indigenous S.cerevisiae strains on the basis of the characteristic development of the production area,three fermentation treatments were set up with’Cabernet Sauvignon’ grapes in the eastern foot of Helan Mountain in Ningxia as raw materials:natural fermentation,direct inoculation CECA fermentation and sterilization inoculation CECA fermentation,and on the first day(before inoculation),the third day(early fermentation),the fifh day(middle fermentation)and the seventh day(late fermentation)of grape crushing,Samples were taken in the fifth period of the 17th day(end of fermentation).The differences of yeast community structure among three fermentation treatments were studied,and the colonization ability of indigenous S.cerevisiae strains CECA was analyzed;At the same time,explore the effects of different fermentation conditions on the main aroma substances,and then clarify the characteristics of fruit aroma produced by indigenous S.cerevisiae strains CECA when fermenting Cabernet Sauvignon wine,so as to provide a theoretical basis for indigenous S.cerevisiae strains CECA to improve the quality of Cabernet Sauvignon wine.The main results are as follows:(1)In this study,742 yeast strains were isolated from five fermentation stages of Cabernet Sauvignon wine,including natural fermentation,direct inoculation fermentation and sterilization inoculation fermentation.These strains of yeast were divided into 6 different species by the morphological classification of WL medium and 26S sequence alignment in D1/D2 region.They were H.uvarum、C.zemplinina、P.kudriavzevii、P.fermentans、M.pulcherrima、S.cerevisae.Moreover,the species and proportion of yeast in different periods showed differences in the three fermentation treatments,nonSaccharomyces cerevisiae were the main species before inoculation,and S.cerevisiae were the main species in the late and late fermentation.However,in the initial and middle stage of natural fermentation,it is mainly H.uvarum.In the initial and middle stage of sterilization inoculation fermentation,almost all of them are S.cerevisiae.In the initial stage of direct inoculation fermentation,S.cerevisiae appears.With the progress of fermentation,the proportion of S.cerevisiae gradually increases.(2)The genetic diversity of S.cerevisiae strains was analyzed by SSR microsatellite marker technology and interdelta fingerprint technology.Among them,S.cerevisiae isolated from natural fermentation showed 42 SSR genotypes and 15 interdelta genotypes.S.cerevisiae isolated from direct inoculation fermentation showed 45 SSR genotypes and 9 interdelta genotypes;S.cerevisiae isolated from sterilized inoculation fermentation showed 32 SSR genotypes and 7 interdelta genotypes.Interdelta fingerprint technology combined with SSR molecular marker method has good discrimination effect at the strain level,but SSR molecular marker technology shows better discrimination ability for different S.cerevisiae strains.Interdelta analysis and SSR analysis showed that the same genotype as indigenous S.cerevisiae strains CECA was not isolated in natural fermentation.In the inoculated fermentation species,the fermentation is completed by the participation of indigenous S.cerevisiae strains and wild yeast,which compete with each other in the fermentation and change in quantity succession.The two analysis results showed that in the direct inoculation fermentation,the competitiveness of indigenous S.cerevisiae strains CECA was weak in the initial stage of fermentation,while wild yeast showed strong competitiveness and occupied the dominant position of fermentation.With the progress of fermentation,indigenous S.cerevisiae strains CECA showed strong competitiveness and became the dominant strain in the middle and late stage of fermentation,The isolated CECA strains account for 48.44%of SSR genotype and 59.63%of interdelta genotype;In the process of sterilization inoculation fermentation,the genotype of indigenous S.cerevisiae strains CECA is the dominant strain in the whole fermentation process,accounting for 78.88%of SSR genotype and 81.87%of interdelta genotype,showing good colonization ability.(3)The aroma components of Cabernet Sauvignon wines under different treatments were determined by headspace solid-phase microextraction combined with gas chromatography-msass spectrometry(HSSPME-GC-MS).The results showed that there was no significant difference in the composition of aroma substances in the three fermented wines,all of which were 50 volatile aroma substances,including 22 esters,16 alcohols,4 acids and 8 other compounds,but there were great differences in the content of aroma substances.Cabernet Sauvignon wine fermented by indigenous S.cerevisiae strains CECA has the characteristics of high ester content and low alcohol content,and the content of esters such as ethyl caproate and ethyl palmitate in directly inoculated fermented wine is significantly higher than that in the other two kinds of fermentation,which brings more rich fruit fragrance such as apple and pineapple to directly inoculated fermented Cabernet Sauvignon wine.Principal component analysis was carried out on aroma substances with odor activity value greater than 0.1.The results showed that the cumulative contribution rate of the two principal components was 62.8%.There were significant differences in the contribution of aroma substances between different fermentation treatments of Cabernet Sauvignon wine samples,and the aroma substances that contributed to the direct inoculation of fermented wine were the most.It also enhances the citrus flavor,tropical fruit flavor and temperate fruit flavor of Cabernet Sauvignon wine.On the whole,although the diversity of yeast in direct inoculation fermentation was lower than that in natural fermentation,the S.cerevisiae treated by this fermentation had rich genetic diversity;The fermentation is completed by the participation of indigenous S.cerevisiae strains and wild yeast.They compete with each other in the fermentation,and the quantity succession changes.The indigenous S.cerevisiae strains CECA has strong competitiveness and shows good colonization ability.In addition,directly inoculated fermented Cabernet Sauvignon wine can stabilize the fermentation process,retain local characteristics and improve the fruit aroma in the wine by inoculating local yeast.Among them,the total content of esters and some esters in directly inoculated fermented wine are higher than those in natural fermentation and sterilized inoculated fermentation,and the content of alcohols is higher than that in sterilized fermentation,so that the wine has more similar flavor characteristics with natural fermentation,It increases the complexity,diversity and pleasure of wine aroma.Therefore,the interaction between CECA and other indigenous S.cerevisiae strains in the fermentation process can improve the quality of wine.The fruit flavor of wine brewed by CECA is prominent,which lays a solid foundation for Ningxia indigenous S.cerevisiae strains CECA to improve the quality of wine in the process of Cabernet Sauvignon wine brewing,and also provides a theoretical basis for the use of S.cerevisiae in the industrial production of wine in this region. |
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