Evaluation of alternative strategies for generating fermentable sugars from high-solids alkali pretreated sugarcane bagasse and successive valorization to L (+) lactic acid

Abstract

Economical bioprocessing of lignocellulosic biomass essentially demands production of fermentable sugars in the concentrated form before their valorization. The present study aimed towards hydrolysis of alkali pretreated sugarcane bagasse at high solid loading and its successive valorization to L (+) lactic acid (LA). Two strategies were evaluated, wherein pretreatment, 12.5% substrate loading, Cellic CTec2 enzyme complex and thermophilic Bacillus coagulans NCIM 5648 were common to the processes. In Process A, when Cellic CTec2 was dosed at 30 FPU g−1 dry biomass, it hydrolyzed 75.8 ± 1.7% cellulose and 88.6 ± 2.1% xylan in 24 h. However, when its loading was changed to 25 mg protein g−1 glucan in Process B, Cellic CTec2 hydrolyzed 72.3 ± 0.3% and 68 ± 0.8% cellulose and xylan respectively. Valorization of glucose-rich filtrates obtained from Process A and B using two different media resulted in 50.4 ± 1.2 g L−1 and 51.24 ± 1.31 g L−1 of LA production from 54.7 to 62.7 g L−1 of glucose respectively. Attaining 1.75–2.4 g L−1 h−1 LA productivity with two scenarios of separate hydrolysis and fermentation is highly encouraging. It opens newer avenues for bio-based LA production using a greener approach.