Influence of Geosmin-Producing Streptomyces on the Growth and Volatile Metabolites of Yeasts during Chinese Liquor Fermentation

Diverse Streptomyces species act as geosmin producers in the Chinese liquor-making process, causing an earthy, off-odor containment. Through microbiological and metabolite analyses, this paper investigates the influence of several geosmin-producing Streptomyces on the microbial community of a brewing system. The antifungal activity against functional liquor-brewing microbes was assayed by an agar diffusion method. Several Streptomyces, most notably Streptomyces sampsonii QC-2, inhibited the growth of the brewing functional yeasts and molds in pure culture. In a simulated coculture, Streptomyces spp. reduced the flavor compounds (alcohols and esters) contributed by yeasts. Nine components in Streptomyces sampsonii QC-2 broth were detected by ultraperformance liquid chromatography coupled with photo diode array (UPLC-PDA), with characteristic ultraviolet absorptions at 360, 380, and 400 nm. The main products of Streptomyces sampsonii QC-2 were identified by ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS/MS), and confirmed by standard mass spectrometry. The antifungal active components were revealed as a series of heptaene macrolide antibiotics.