Lactic acid fermentation of sugars produced by fast pyrolysis of cellulose and effects of by-products on fermentation

Abstract

Saccharification of cellulose is a crucial step in the conversion of biomass into bio-based chemicals and fuels. Among various saccharification methods, fast pyrolysis of cellulose was conducted, resulting in the production of bio-oil containing levoglucosan as the major component, along with various by-products such as glycolaldehyde, glyoxal, methylglyoxal, furfural, 5-hydroxymethylfurfural, acetic acid, formic acid, and formaldehyde. The levoglucosan in the bio-oil was hydrolyzed into glucose and used as a sugar solution for lactic acid fermentation. However, the presence and concentrations of these by-products significantly affected the fermentation process. The inhibitory effects of the by-products were ranked in the order of aldehydes > organic acids > furans, as these compounds interfere with the microbial activity necessary for efficient lactic acid production. To address this issue, an ion-exchange resin containing amino groups was utilized to purify the sugar solution by selectively removing the aldehyde-containing compounds, which comprise the majority of inhibitory substances. This purification enabled successful lactic acid fermentation, even at sugar concentrations that were previously inhibitory. These findings highlight the potential of bio-oil derived from cellulose pyrolysis as a sustainable feedstock for bioprocessing, provided that effective purification strategies are implemented.