Enhanced enzymatic digestibility of steam-exploded short rotation hardwood species Betula pendula and its potential for lactic acid production

Biomass from the dedicated woody crops is a promising source of lignocellulose-based material for producing bio-based products like lactic acid. This work addresses for the first time a process conversion of the hardwood species Betula pendula biomass into lactic acid through steam explosion pretreatment, enzymatic hydrolysis and lactic fermentation of the obtained sugars. Steam-explosion-pretreated Betula pendula biomass displayed significant changes in biomass composition compared to raw material that led to a remarkable enhancement of enzymatic digestibility of the pretreated material, reaching maximum enzymatic hydrolysis conversion yield of cellulose and xylan of 96.2 and close to 96%, respectively, in enzymatic hydrolysis tests at low solid consistency (5% ( w/v )). The optimization of enzyme dosage in enzymatic hydrolysis experiments at 15 and 20% ( w/w ) solid loads allowed successfull enzymatic hydrolysis runs in a high solids bioreactor that resulted in reaction broths containing close to 113 g·L -1 of sugars after 48 h enzymatic hydrolysis, which are subsequently used for lactic fermentation. Both the results of enzymatic digestibility of pretreated material in tests at low and high solid loadings reflect the high suitability of steam explosion technology to pretreat Betula pendula biomass, resulting in carbohydrate conversion yields and final sugar concentrations much superior than those found with other hardwoods. Here, 88.8 g·L -1 of lactic acid were produced by Heyndrickxia coagulans DSM 2314, at a yield of 0.923 g·g -1 (g lactic acid per g monosaccharides) and an average productivity of 1.92 g·L -1 ·h -1 . These promising fermentation results point to good prospects for obtaining lactic acid from Betula pendula . • Bioconversion of Betula pendula (BP) biomass into lactic acid is shown to be feasible. • Steam explosion (SE) pretreatment enhances BP biomass properties for sugar production. • High yields of enzymatic hydrolysis in SE treated BP, at high solid load conditions. • Selection of the Heyndrickxia coagulans strain with better fermentation performance. • High lactic acid fermentation yields are achieved.