Holistic fractionation of spent yerba mate via a mild, two-stage flow-through ethanosolv process

Abstract

Biorefineries capitalize the potential of lignocellulosic biomass to substitute fossil carbon for the chemical industry. In this study, the polyphenol-rich (27.4 wt%) lignocellulosic waste derived from the consumption of yerba mate was used as feedstock for fractionation towards valuable chemical products. HSQC NMR characterization of the polyphenol-rich fraction revealed that even after industrial processing and consumption, the lignin polymer of yerba mate still conserves a high β-O-4 content of 51 linkages per 100 C9 units and a S/G ratio of 1.4. The removal of extractives with ethanol and subsequent mild acid-catalyzed ethanosolv lignin extraction were performed on the spent yerba mate in a single flow-through reactor. This process yielded 19.3 wt% of extractives and 68% of the initial polyphenol fraction. The recovered phenolic-rich fraction showed high preservation of the lignin aryl ether structure, evidenced by the retention of 51 β-O-4 linkages per 100 C9 units. The extracted aqueous carbohydrate fraction containing a mixture of monomeric ethyl glycoside structures was quantified with a dedicated method achieving 94% mass-balance closure. Finally, the saccharified glucan-rich residue from the ethanosolv process was used to showcase the production of polyhydroxybutyrate, achieving a yield of 37 mg PHB/g monosaccharides by the thermophilic bacterium Tepidimonas taiwanensis LMG 22826.