Robust yeast strains with high inhibitors tolerance remain a critical requirement for the production of lignocellulosic bioethanol. These stress factors are known to severely hinder yeast growth and fermentation performance (J\uf6nsson et al., 2013). This study aims at the design of industrial yeast suitable for the lignocellulose-to-bioethanol route. Grape marc was selected as extreme environment to search for innately tolerant yeast because of its limited nutrients, exposure to solar radiation, weak acid and ethanol content (Favaro et al., 2013 and 2014). One hundred and twenty Saccharomyces cerevisiae strains were recently described to have inhibitors, temperature and osmotic tolerance greater than those exhibited by industrial strains and showed remarkable potential for bioethanol production.
With the aim of further investigating their industrial fitness, a Fourier Transform InfraRed Spectroscopy (FTIR)-based bioassay was employed to explore the yeast metabolomic and viability responses to inhibitors. Three different strains of S. cerevisiae (Fm17, Fm84 and DSM70049) were chosen as representative for the top, medium and low inhibitors tolerance. The yeast were exposed to acetic acid, formic acid, furfural and 5-hydroxymethyl-2-furaldehyde (HMF) and analysed by a FTIR-based assay to detect the extent of the metabolomic stress, the type of response and the induced mortality. To deeper investigate the effect of the co-presence of inhibitors on yeast metabolism, FTIR analysis was also conducted on yeast cells challenged with mixtures composed by increasing dosages of each single inhibitory compound
