Lignin Molecular Modification Enhancing Its Bioaccessibility and Biotransformation

Lignin typically exhibits poor dispersibility in aqueous fermentation media, which restricts microbial conversion. In this study, enzymatic hydrolysis lignin (EHL) was modified by introducing hydrophilic functional groups to enhance its bioaccessibility. The average effective diameter of colloidal particles in EHL, hydroxymethylation-modified EHL (H-EHL), carboxymethylation-modified EHL (C-EHL), coupled hydroxymethylation-aminated EHL (HA-EHL), and coupled carboxymethylation-aminated EHL (CA-EHL) media was 278, 224, 263, 181, and 169 nm, respectively. Rhodococcus opacus PD630 was employed for lignin bioconversion into lipids. The cell dry weight in H-EHL, C-EHL, HA-EHL, and CA-EHL media increased by 37%, 31%, 57%, and 44%, respectively, than EHL. Correspondingly, lipids production increased across all modified lignin media, particularly in HA-EHL medium, increasing by 41% over EHL. β-O-4 and β-β linkages were degraded most significantly in HA-EHL, indicating a more efficient bioconversion of HA-EHL than other lignins. Overall, molecular modifications improved lignin's dispersibility in aqueous fermentation media, which further promoted lignin biotransformation.