Structural characterization and enzymatic hydrolysis of lignin-carbohydrate complex in corn bran: Pretreatment-induced variations in structure and recalcitrance

Lignin-carbohydrate complex (LCC) is a critical yet understudied determinant of corn bran (CB) recalcitrance, so clarifying its structural features is essential for CB efficient utilization. Herein, Björkman LCCs, isolated from destarched CB (CB-BjLCC) and autohydrolysis residues (residue-BjLCCs), were comprehensively characterized to elucidate pretreatment-induced structural variations and the consequent impact on enzymatic hydrolysis. CB-BjLCC differed from typical herbaceous LCCs by exhibiting a glucan-rich composition (58% of total carbohydrates), lignin dominated by H and G units, and phenyl glycoside (PhGlc) linkages as the predominant LC linkage type (42.67/100Ar). Particularly, the polysaccharide in CB-BjLCC is dominated by mixed-linkage β-1,3/1,4-glucan, accompanied by lower amounts of xyloglucan and cellulose, and associated with highly substituted glucuronoarabinoxylan (GAX). Autohydrolysis shifted the dominant polysaccharide in residue-BjLCCs toward GAX, while both the branching degree of GAX and the abundance of LC linkages decreased with extended pretreatment time. Notably, PhGlc linkages declined sharply by 69–88%, and this reduction in structural complexity thus enhanced monosaccharide yields from autohydrolysis residues and residue-BjLCCs. These findings provide new insights into CB recalcitrance, highlighting the heterogeneous glucan-rich LCC and significant changes in LCC composition and structure depending on pretreatment intensity.