L-lactic acid production from multi-supply autohydrolyzed economically unexploited lignocellulosic biomass

Abstract

The present paradigm of a new concept of biomass conversion system has been focused on the development of a multi-supply biorefinery concept towards a circular and sustainable bioeconomy. This work was focused on evaluating a mixture of six lignocellulosic biomass types, from forest ecosystems and biological resources from marginal land, in order to produce lactic acid (L-LA) by Lactobacillus rhamnosus within a multi-supply biorefinery scheme. The mixture of lignocellulosic biomass was submitted to autohydrolysis pretreatment under non-isothermal regime at 226 °C (corresponding to a severity of 4.15) yielding a glucan recovery of 93 % in the solid phase. Two different strategies were assayed for L-LA production, namely separated hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). The glucose to LA yield obtained for both assays was 1 g/g, although the volumetric productivity of SSF (2.5 g/Lh) was higher than SHF (0.8 g/Lh). Therefore, the SSF process was optimized through a factorial design to evaluate the effect of the independent variables, solids load (SL) and enzyme-substrate ratio (ESR), on LA production. The maximum concentration of LA was obtained using the highest solids load (16 %) and with the highest ESR (54 FPU/g). Finally, L-LA was produced using in a bioreactor under the optimized conditions from experimental design, obtaining 61.74 g/L of LA at 44 h, with an optical purity of 98 % and a LA yield of 0.97 g/g. This study showed the potential of multi-supply unexploited lignocellulosic biomass as a raw material to LA fermentation.