低含水量条件下大曲中抑制土味素的功能微生物解析

Analysis of the geosmin-inhibiting microorganismsin Daqu under low water content

土味素是链霉菌属的特征挥发性代谢产物,在痕量级别(阈值在ng/L水平)会引起泥土异味,严重破坏中国白酒的风味与品质。大曲制造过程中含水量随时间下降,制曲后期含水量约为10%时,可检测到约为6μg/kg的土味素,严重影响大曲的质量。从大曲中筛选在低含水量条件下抑制土味素产生的功能微生物用于生物防治是提升大曲质量的必要手段。该研究对中温大曲中的微生物群落结构和土味素含量进行分析,并筛选能够抑制土味素的原位功能微生物。研究结果表明,制曲后期,含水量下降至10%~20%,土味素含量仍在上升,达到最高质量分数(9.75±0.50)μg/kg。大曲中主要的真菌为毕赤酵母属(Pichia)、嗜热子囊菌属(Thermoascus)等。基于Spearman等级相关性分析筛选出了6株对链霉菌有较好抑制作用的真菌Aspergillus sp.LBM32010、Aspergillus sp.LBM32013、Rhizopus sp.LBM32021、Trichosporon sp.LBM32022、Lichtheimia sp.LBM32026和Trichosporon sp.LBM32030,其中Aspergillus sp.LBM32010对土味素的抑制效果最好,在模拟实验中发现土味素含量从(34.79±2.34)μg/kg下降至(3.11±1.22)μg/kg,抑制率为91.06%(P<0.001)。该研究发现了大曲中原位微生物对痕量级别挥发性有机物具有防治的潜力,可通过靶向调控微生物群落解决大曲中土味素污染问题。

Geosmin is a volatile metabolite of Streptomyces spp.,which causes earthy off-flavor at trace level content(the threshold is at ng/L level),seriously and extensively deteriorating the flavor and quality of Chinese Baijiu.The water content in Daqu(Chinese Baijiu fermentation starter)-making process decreased with time.When the water content was about 10%in the late stage,about 6μg/kg of geosmin could be detected,which seriously affected the quality of Daqu.Screening of functional microorganisms from Daqu that inhibit the production of geosmin under low water content conditions for biocontrol is a necessary mean to improve the quality of Daqu.In this study,the microbial community structure and the geosmin content in Daqu were analyzed,and obtained the in situ functional microorganisms of Daqu according to the inhibition of Streptomyces.The results showed that in the late stage of Daqu-making,the water content decreased to 10%-20%,and the geosmin content was still increasing,reaching the highest content of(9.75±0.50)μg/kg.The main fungi in Daqu were Pichia,Thermoascus.Based on Spearman’s correlation analysis,it was found that Aspergillus sp.LBM32010,Aspergillus sp.LBM32013,Rhizopus sp.LBM32021,Trichosporon sp.LBM32022,Lichtheimia sp.LBM32026 and Trichosporon sp.LBM32030 have good inhibitory effects on Streptomyces and geosmin,among which Aspergillus sp.LBM32010 had the best inhibitory effect on geosmin,and geosmin content decreased from(34.79±2.34)μg/kg to(3.11±1.22)μg/kg,and the inhibition rate was 91.06%(P<0.001).This study highlights the biocontrol feasibility potential of the chemicals at trace level by precise regulation of microbial communities,and shows the possibility of achieving precise regulation of microbial communities.