Oligosaccharide-phenolic compound conjugates in soluble polysaccharides from rice straw alleviate ethanol fermentation stresses in Saccharomyces cerevisiae

Abstract

In this study, it was found that soluble polysaccharides (SPs) from rice straw were conjugated with high levels of phenolic compounds. A gradient ethanol precipitation method was used to separate conjugates with different phenolic compound components. These conjugates were mainly composed of disaccharides or trisaccharides and phenolic acids that were mainly p-coumaric acid, ferulic acid, vanillic acid, and vanillin. SPs with more conjugates exhibited better effects on Saccharomyces cerevisiae and ethanol fermentation. The change in the proportion of conjugates in SPs significantly affected the accumulation of intracellular trehalose and glycerol content, indicating the effect of the conjugates on intracellular osmotic stress. Moreover, SPs with more conjugates generated lower intracellular hydrogen peroxide (H2O2) levels. Thus, oligosaccharide and phenolic compound conjugates in SPs promoted yeast growth and ethanol fermentation. For instance, OD value reached 9.4, which was 1.3 times higher than the control group, and ethanol content at 36 h was 36.5 g/L, which was 1.3 times higher than the control. Osmotic pressure alleviation and lowered intracellular H2O2 levels by conjugates are key mechanisms of the SPs during yeast growth and ethanol fermentation.