Impact of the presence of lignin on the enzymatic hydrolysis of wheat straw

Second-generation bioethanol biomass is investigated since decades as alternative to fossil fuels. Due to the cost of enzymes, the hydrolysis step stays one of the main bottlenecks of the process. As a consequence, the action of enzymes must be facilitated by first reducing the inherent recalcitrance of the substrate. This recalcitrance is partly linked to the presence of lignin. Lignin is known to hinder the enzymatic hydrolysis of biomass, since cellulases may adsorb on its surface in a non-productive way and lose access to a part of cellulose. However, the involved phenomena remain unclear and the impact of lignin on the enzymatic hydrolysis is still difficult to predict.

The purpose of this work is to better understand the role of lignin in the recalcitrance of biomass during enzymatic hydrolysis. For that, a pretreated wheat straw has been partially delignified by acidified sodium chlorite in order to obtain six grades of delignification. Their respective hydrolysis reactivity have then been compared using an enzymatic cocktail from Trichoderma reesei. It appears that the different grades of delignification do not have a significant impact on the hydrolysis. Inhibitive impact of lignin in terms of non-productive adsorption has then been explored using soda lignin from wheat straw. The addition of this particular type of lignin had a strong negative influence on the hydrolysis of a highly crystalline cellulose (Avicel), whereas it impacted only slightly the hydrolysis of delignified wheat straw. These findings comfort the previous results and complete other similar works carried on wood.