The structural changes of lignin and lignin–carbohydrate complexes in corn stover induced by mild sodium hydroxide treatment

Abstract

Non-woody biomass such as corn stover is a very abundant and sustainable biofuel feedstock in the US whose technical hurdles for enzymatic hydrolysis have not been adequately addressed. There is very little useful data on the lignin and the lignin–carbohydrate complexes of corn stover and the impacts of them on bioconversion to fermentable sugars. The following principal tasks were addressed, which will help to develop the roadmap of effective saccharification of corn stover: (1) corn stover was separated into stem, cob, and leaf; (2) lignin (cellulolytic enzyme lignin, CEL) and lignin–carbohydrate complexes (milled wood lignin, MWLc) were isolated from the extractive-free and the alkaline-treated samples, respectively; and (3) the structural changes of lignin and lignin–carbohydrate complexes (LCCs) were characterized by alkaline nitrobenzene oxidation, 13C, and 1H–13C HSQC NMR. The results indicated: (1) a significant amount of p-coumarate and ferulate esters was identified and quantified; (2) lignin of the alkaline-treated sample was more condensed; (3) an unanticipated amount of LCCs was quantified in the extractive-free sample, however, the amount of LCCs decreased significantly with the alkaline treatment. Therefore, lignin and LCCs of the treated sample should be characterized to elucidate their effects on the enzymatic saccharification.