Fermentative valorisation of xylose-rich hemicellulosic hydrolysates from agricultural waste residues for lactic acid production under non-sterile conditions

Lactic acid (LA) is a platform chemical with diverse industrial applications. Presently, commercial production of LA is dominated by microbial fermentation using sugary or starch-based feedstocks. Research pursuits emphasizing towards sustainable production of LA using non-edible and renewable feedstocks have accelerated the use of lignocellulosic biomass (LCB). The present study focuses on the valorisation of xylose derived from sugarcane bagasse (SCB) and olive pits (OP) through hydrothermal and dilute acid pretreatment, respectively. The xyloserich hydrolysate obtained was used for LA production by homo-fermentative and thermophilic Bacillus coagulans DSM2314 strain under non-sterile conditions. The fed-batch mode of fermentation resulted in maximum LA titers of 97.8, 52.4 and 61.3 g/L with a yield of 0.77, 0.66 and 0.71 g/g using pure xylose, xylose-rich SCB and OP hydrolysates, respectively. Further, a two-step aqueous two-phase system (ATPS) extraction technique was employed for the separation and recovery of LA accumulated on pure and crude xylose. The LA recovery was 45 - 65% in the first step and enhanced to 80-90% in the second step.The study demonstrated an efficient integrated biorefinery approach to valorising the xylose-rich stream for cost-effective LA production and recovery.

Automated summary

This study focused on the valorization of xylose derived from sugarcane bagasse and olive pits through hydrothermal and dilute acid pretreatment. The xylose-rich hydrolysate obtained was used for lactic acid (LA) production using a thermophilic Bacillus coagulans strain under non-sterile conditions. The maximum LA titers obtained were 97.8, 52.4, and 61.3 g/L with yields of 0.77, 0.66, and 0.71 g/g using pure xylose, xylose-rich sugarcane bagasse, and olive pit hydrolysates, respectively. A two-step aqueous two-phase system (ATPS) was employed for the recovery of LA from the xylose-rich stream, resulting in a recovery rate of 80-90%.