Inhibitory Effect Of Enhanced Composite Microbial Agents On Geosmin In Daqu

The pollution caused by Streptomyces and its characteristic metabolite geosmin（GSM）has always been a serious problem in Chinese liquor industry.Daqu,as an important raw material for liquor fermentation,was detected with a high geosmin content.The threshold of geosmin is extremely low,the geosmin content in Daqu was higher than 5μg·kg^-1,which would lead to obvious earthy odor in Chinese liquor,which would seriously damage the flavor and quality of Chinese liquor.Daqu making process is a multi-species process in an open and complex system.It is difficult to realize the precise regulation of the microgram-level compound geosmin under such complex system.To fill this gap,from the perspective of fermentation micro-ecology,the possible antagonism between microorganisms was used to explore the microorganisms that have inhibitory effects on Streptomyces.We explored a multi-strain combination biocontrol method to control the biomass of Streptomyces and the content of geosmin from the source,and improve the quality of Daqu.In this study,medium temperature Daqu were taken as the study object,and Streptomyces albus FXJ was selected as the representative microorganism of the genus Streptomyces.Headspace-solid phase microextraction combined with gas chromatography-mass spectrometry（HS-SPME-GC-MS）was used to determine the geosmin and other volatile flavor compounds in Daqu,real-time quantitative PCR（q PCR）technology was used to quantitative analysis the biomass of Streptomyces in Daqu,and the microbiome research methods was used to analysis the microbial structure of Daqu.This study highlights the ability of biocontrol as an environmentally friendly method to regulate the microgram-level compounds in complex systems,and highlights the possibility of achieving precise regulation of microbial communities.The main results are as follows:（1）First of all,the geosmin content in Daqu of the two most seriously polluted Chinese liquor factories was clarified.Herein,six strains including Pichia sp.,Saccharomyces sp.,and Bacillus sp.were obtained according to the inhibitory on Streptomyces albus FXJ growth.After the combination,it was applied in the actual production process of medium temperature Daqu as the geosmin-inhibiting microorganism.The application effect of geosmin-inhibiting microorganism in Daqu was analyzed through the changes of geosmin content,physicochemical indexes and volatile flavor compounds.The results showed that the geosmin content in the two liquor factories was more than 5μg·kg^-1,and the liquor had obvious earthy odor.The results of geosmin-inhibiting microorganism intervention showed that,geosmin-inhibiting microorganism intervention has the ability to reduce the geosmin content in Daqu,at the end of Daqu making process,the geosmin content was lower than 5μg·kg^-1,and the maximum concentration reduction ratio was 54.6%.After the geosmin-inhibiting microorganism intervention,the liquefying power,saccharifying power and esterifying power of Daqu were increased by 13.5%,25.7%and 69.7%,respectively.Meanwhile,the geosmin-inhibiting microorganism intervention significantly increased the volatile flavor compounds in Daqu such as 1-hexanol,ethyl acetate,3-methyl-1-pentanol,heptanol,ethyl 2-methylbutyrate,phenethyl alcohol,hexanal and 3-methylbutanal.Therefore,the geosmin-inhibiting microorganism has a positive effect on Daqu in terms of application effect.（2）Then,the effect of the geosmin-inhibiting microorganism intervention on the microbial community structure of Daqu was analyzed.Real-time quantitative PCR analysis highlighted that the geosmin-inhibiting microorganism intervention effectively reduced the biomass of Streptomyces in Daqu.The microorganism genomics was employed to reveal the microbial community diversity and structure during Daqu making process,and reveal the geosmin-inhibiting microorganism action time and action position.Pichia and Saccharomyces in the geosmin-inhibiting microorganism mainly played an important role in the early stage of Daqu making process,while Bacillus in the geosmin-inhibiting microorganism mainly played an important role in the late stage of Daqu making process,and the geosmin-inhibiting microorganism has a more significant effect on the rind of Daqu.Principal-component analysis（PCA）combined with permutational multivariate analysis of variance（PERMANOVA）highlighted that the geosmin-inhibiting microorganism can realize the purpose of precise regulation of geosmin by regulating the content of microorganisms that have an inhibitory effect on Streptomyces without destroying the original microbial community structure of Daqu.Microbial community correlation network analysis showed that the content of microorganisms also had important role in shaping Daqu microbiota interaction.（3）Finally,in practical application of geosmin-inhibiting microorganism,it was found that that the inhibitory effect of geosmin in Daqu has the possibility of further improvement.It was found that water content was the key factor affecting the geosmin content in Daqu.In view of the phenomenon that the water content of Daqu decreased to 10%-20%in the later stage,and the geosmin content appeared a secondary increase phenomenon,a new idea of strain combination under the low water content condition was proposed.Combined with Spearman’s rank correlation analysis and culture-dependent experiments,the fungi that inhibited Streptomyces under the low water content condition were obtained.Determination of the growth ability and the inhibitory ability of geosmin in simulated culture under low water content conditions.Among which two microorganisms,Aspergillus sp.and Rhizopus sp.,showed the best geosmin inhibitory ability,and the maximum geosmin concentration reduction ratio was91.06%（P<0.001）.