Reducing agents improve enzymatic hydrolysis of cellulosic substrates in the presence of pretreatment liquid

Enzymatic hydrolysis of pretreated lignocellulosic substrates has emerged as an interesting option to produce sugars that can be converted to liquid biofuels and other commodities using microbial biocatalysts. Lignocellulosic substrates are pretreated to make them more accessible to cellulolytic enzymes, but the pretreatment liquid partially inhibits subsequent enzymatic hydrolysis. The presence of pretreatment liquid from Norway spruce resulted in a 63% decrease in the enzymatic saccharification of Avicel compared to when the reaction was performed in a buffered aqueous solution. The addition of 15 mM of a reducing agent (hydrogen sulfite, dithionite, or dithiothreitol) to reaction mixtures with the pretreatment liquid resulted in up to 54% improvement of the saccharification efficiency. When the reducing agents were added to reaction mixtures without pretreatment liquid, there was a 13–39% decrease in saccharification efficiency. In the presence of pretreatment liquid, the addition of 15 mM dithionite to Avicel, α-cellulose or filter cake of pretreated spruce wood resulted in improvements between 25 and 33%. Positive effects (6–17%) of reducing agents were also observed in experiments with carboxymethyl cellulose and 2-hydroxyethyl cellulose. The approach to add reducing agents appears useful for facilitating the utilization of enzymes to convert cellulosic substrates in industrial processes.

► Pretreatment liquid inhibited enzymatic hydrolysis of cellulose.
► Addition of reducing agents to the pretreatment liquid made enzymatic hydrolysis of cellulose more efficient.
► Without pretreatment liquid, inclusion of reducing agents had a negative effect on the enzymatic hydrolysis.
► The reducing agents investigated includedhydrogen sulfite, dithionite, and dithiothreitol.