Influence of dilute acid hydrolysis conditions and hydrolysate treatment sequences in the production of fermentable sugars from sugarcane bagasse and straw for xylitol production

The biotechnological production of xylitol has been widely studied in the literature; however, its industrial-scale implementation remains challenging due to non-standardized operating conditions and variations in processing sequences. This study evaluated key process conditions (acid concentration, biomass load, and reaction time) in two different hydrolysate production sequences using sugarcane bagasse and straw mixture. The results showed that the sequence in which the hydrolysate was neutralized in the first step and concentrated in the last step resulted in higher sugar recovery and less formation of inhibitors. The optimal conditions were identified as 2 % (w/v) sulfuric acid, biomass load of 5 % (w/v), and reaction time of 30 min. Fermentation of the raw hydrolysate obtained under these optimal conditions presented inhibition in xylitol production, but supported biomass growth, possibly due to the carbon-to‑nitrogen ratio in the medium. Further assays revealed that the addition of an organic nitrogen source (yeast extract) to the medium enhanced biomass growth and xylitol production. Based on the results, an alternative process sequence with hydrolysis conditions optimized to maximize xylose recovery was proposed. Additionally, the combined synergistic effects of inhibitors (acetic acid, formic acid, furans, and phenols) on the metabolism of Candida tropicalis were also studied.