Repeated cultures of Saccharomyces cerevisiae SC90 to tolerate inhibitors generated during cassava processing waste hydrolysis for bioethanol production

Abstract

Large amount of cassava pulp is produced as by-product of industrial tapioca production. The value-added process of this low-cost waste is to use it as a substrate for bioethanol production. However, during the pulp pretreatment by acidification combined with steam explosion, many yeast inhibitors including acetic acid, formic acid, levulinic acid, furfural and 5-hydroxymethylfurfural are generated and these compounds have negative effects on the subsequent fermentation step. Therefore, the objective of this study was to investigate whether the repeated cultures of Saccharomyces cerevisiae SC90 could alleviate this problem. To obtain the inhibitor tolerable cells, the repeated culture was performed by growing yeast cells to a specific growth rate (µ) of 0.22 h −1 or higher (80% of the µ in control) and then transferring them to progressively higher concentrations of hydrolysate ranging from 20 to 100% (v/v). The results showed a tendency of longer lag phase as well as time to reach maximum cell number (t maxc) with an increase in hydrolysate concentration. However, the repeated culture at the same hydrolysate concentration could shorten both lag period and t maxc. Interestingly, the growth and fermentation efficiency of adapted cells in 100% hydrolysate were significantly higher (p ≤ 0.05) than those of non-adapted cells by 38% and 27%, respectively.

Overcoming lignocellulose‐derived microbial inhibitors: advancing the Saccharomyces cerevisiae resistance toolbox

“…The use of lignocellulose hydrolysates allows for a more realistic representation of inhibitor molecules because compounds may exhibit synergistic inhibitor mechanisms. In one instance, S. cerevisiae SC90 was adapted to increasing concentrations of cassava pulp hydrolysate, culminating in isolates with enhanced growth (38%) and fermentation ability (27%) in 100% v/v hydrolysate, relative to the control strain . Adaptation in lignocellulose hydrolysates was also used in visualizing evolution in real time (VERT) experiments to determine the genetic determinants inherent in inhibitor resistance phenotypes .…”