Evaluation of inhibition kinetics of furfural, 5-hydroxymethylfurfural and acetic acid on xylitol fermentation by Pichia stipitis

The valorization of agro-industrial residues involves the prerequisite pretreatment process followed by bioconversion using microorganisms for the production of value-added products. Hemicellulose present in agro-industrial residues up to 35% is a sustainable source of xylose for xylitol production. Pretreatment process required for xylose-enriched liquid hydrolysate generates inhibitors which affects xylitol fermentation. This study was therefore, evaluated to understand the insights of inhibitory effects of furfural, HMF and acetic acid on xylitol fermentation by Pichia stipitis. The results indicated that effect of inhibitors on xylitol fermentation was: furfural > acetic acid > HMF. Individually furfural (500 mg/L) and acetic acid (1000 mg/L) reduced the xylitol yield by up to 59% and 44%. The synergistic effect of 500 mg/L furfural, 500 mg/L HMF and 1000 mg/L acetic acid showed the highest reduction in xylitol yield of 67.6% as compared to the control. Kinetic studies predicted that the maximum concentration of furfural, HMF and acetic acid which affected P. stipitis growth was 84.48 mg/L, 3258.42 mg/L and 2921.93 mg/L. The maximum inhibitor concentration above which xylitol production was inhibited at 1069.55 mg/L furfural, 3498 mg/L HMF and 3714.50 mg/L acetic acid.