The Effect Of Oxidoreduction Potential On Yeast Stress Response

Lignocellulose is the second raw materials for fuel ethanol after the first generation biomass food crop such as corn and the 1.5 generation non-food crops such as cassava. Lignocellulose takes many advantages such as large storage, high annual productivity and without seasonal restrictions, etc. However, during cellulosic ethanol fermentation, yeast cells have to face various stressful conditions like inhibitors in hydrolysate including acetic acid, furfural and phenol, and harsh environments such as high temperature, osmotic pressure and low pH. In this study, oxidoreduction potential (ORP) was introduced to control ethanol fermentation, which had effects on cell stress tolerance. Besides, metabolomic analysis of yeast under very high gravity (VHG) ethanol fermentation was especially focused on. The main conclusions were as below:With the presence of the inhibitors, the oxidizing state can enhance the formation of biomass, thereby improve the fermentation. Under the phenol stress, the oxidizing state improved the ethanol yield. All addition of redox agent promoted glycerol synthesis because of the altered metabolic flux. ORP control benefited the removal of inhibitors, and the detoxification ability of three inhibitors were acetic acid> furfural> phenol.Under three different stressful conditions, high temperature, high concentration of sugar and ethanol, the supplement of oxidizing agent can accelerate cell growth, probably due to oxidizing state activated cellular anti-oxidant pathways, which resulted in massive synthesisThe profile of ORP reflects yeast growth and ethanol production. In VHG ethanol fermentation, the efficiency was the best when ORP was controlled at-150 mV. Cluster analysis showed that the distance among four kinds of fermentation directly related to the amount of dissolved oxygen. Principal component analysis, PCA found that cells generated more rare metabolites at-150 mV compared with others. Metabolomic analysis showed that accumulation of intermediate carbohydrates, amino acids and reducing power, which always present under ethanol stress, were decreased at-150 mV, indicating that ORP may ease the ethanol stress.Furthermore, the Logistic growth model was applied to analysis the acetic acid tolerance. The parameters K values, tE0.5 and tB.s reflect the maximum biomass, ethanol productivity and specific growth rate. The results showed that cell can well adapt the acetic acid under proper initial conditions such as inoculation and aeration.This work indicates the feasibility of ORP control strategy to improve the ability of cells stress tolerance, which not only provids the scientific important reference, but also practical significance in cellulosic ethanol industry.