Investigating the secretome of non-Saccharomyces yeast in model wine

[摘要] ENGLISH ABSTRACT: Proteins from various sources, including grape berry cells, yeast, bacteria and fining agentse.g. albumin and casein, have previously been identified in wine. These proteins play variouscritical roles in the functioning and survival of the organisms that produced them but alsoexhibit oenological properties, once secreted in the juice/wine. Some of them can indeed bebeneficial to winemaking, by releasing aroma compounds from grape-derived precursors, ordetrimental to wine quality, by causing protein haze. Yeasts contribute significantly to theprotein pool during and after alcoholic fermentation. However, while the extracellular proteinsof Saccharomyces cerevisiae, the main wine yeast species, have been characterised, thoseof non-Saccharomyces yeasts remain largely unknown, especially under winemakingconditions. Although specific extracellular enzymes released by non-Saccharomyces yeastshave been the focus of many studies in recent years, the targeted approaches used haverestricted our knowledge to these specific enzymes and excluded the other secretedproteins. A more comprehensive insight into entire secretomes could improve ourunderstanding of how yeasts survive in wine and interact with other species in mixed culturefermentations.This study aims to characterise the exo-proteome of Saccharomyces and selectednon-Saccharomyces yeasts in pure and mixed cultures in a wine-like medium.Fermentation kinetics were monitored and the extracellular proteins isolated at the end offermentation. M. pulcherrima hardly fermented whereas L. thermotolerans fermented slowlybut steadily. As expected S. cerevisiae completed the fermentation rapidly. In sequentialfermentations, the kinetics resembled those of the non-Saccharomyces yeasts for a periodbefore switching to that of S. cerevisiae. This period varied from 4 to 15 days for M. pulcherrima and L. thermotolerans respectively.Visual observations of the protein content of the medium at the end of fermentation using 1Dand 2D SDS-PAGE gels as well as identification of these proteins using mass fingerprintingrevealed the large variety of proteins secreted and the influence of yeast interactions oneach other's secretome. The fermentation kinetics observed could partially be explained bythe extent of the contribution of the different yeast to the protein content.Proteins secreted by non-Saccharomyces yeasts lowered the potential of wine to formprotein haze, with both M. pulcherrima and L. thermotolerans in pure and mixed culturefermentations showing lower haze formation than S. cerevisiae.As far as we know, this is the first report on the secretome of non-Saccharomyces underwinemaking condition and the influence non-Saccharomyces proteins have on the proteinhaze potential of wine, providing the basis for future investigations.

[发布机构] Stellenbosch University