(144e) Towards Valorization of Biorefinery Waste to Polyhydroxyalkanoate: Structural Characterization and Mechanisms

The large-scale production of cellulosic ethanol from lignocellulosic biomass are generating lignins which have high potential to be transformed to sustainable high-value products. Sustainable production of polyhydroxyalkanoate (PHA) using lignin as carbon source provides a promising valorization pathway of lignin. In this study, four lignin streams generated from different fractionation strategies (integrating acid/alkali pretreatment, enzyme hydrolysis, and laccase pretreatment) from corn stover were used in fed-batch fermentation to produce PHA by P. putida KT2440. The lignin streams before and after subjecting to the fermentation process as well as the native lignin from corn stover were thoroughly characterized by gel permeation chromatography (GPC), ³¹P nuclear magnetic resonance (NMR), two-dimensional (2D) heteronuclear single-quantum coherence (HSQC) NMR spectroscopy, and ¹⁹F NMR. The GPC data showed that the fractionation processes significantly lower the molecular weight of lignin steams; the polydispersity (PDI) of the lignin streams decreased after the fermentation step with a highest reduction percentage of 50.8%, which may suggest that the lower molecular weight components were more favorable for P. putida KT2440 and the molecular weight distribution of lignin streams became uniform. ³¹P NMR analysis examined the hydroxyl group changes after the fractionation and fermentation processes. Semi-quantitative HSQC data proved that the p-hydroxyphenyl lignin may promote the lignin conversion to PHA; more than 78% p-coumarate and 15% ferulate structures in lignin steams from three fractionation strategies were consumed, which suggest that consumption of hydroxycinnamates contributed to the production of PHA. ¹⁹F NMR analysis achieved the quantification of carbonyl groups in lignin stream; the fermentation generally consumed more than 50.4% aldehyde, ketone, and quinone structures in lignin steam.