Separation and characterisation of glyceryl glycosides and lignin from acid-catalysed glycerol pretreatment hydrolysate of sugarcane bagasse

Abstract

Acid-catalysed glycerol (ACG) pretreatment of biomass is one of the pre-treating techniques for the enzyme-mediated lignocellulosic biorefinery, while inadequate attention has been paid to the glycerol modified saccharides and lignin redistributed to the hydrolysate, nor their bioactive properties. In this study, a sequential process involving tetrahydrofuran (THF) extraction and carbon/celite adsorption-elution was employed to recover lignin and glyceryl glycosides (GG) from ACG hydrolysate. The physicochemical and structural properties of lignin were systematically explored, and were related to their antioxidation properties, the composition and moisturising activities of GG was investigated. Two types of lignin i.e., water-insoluble lignin (WIL) and water-soluble lignin (WSL) were obtained, accounting for 49.60 wt% and 38.00 wt% of the total lignin in raw bagasse, respectively. GG separated from the hydrolysate yielded an overall recovery of 68.17 wt% of the xylan from the raw bagasse. The relatively high yield of lignin and GG can be attributed to the incorporation of glycerol molecules. 2D HSQC NMR results revealed that glycerol effectively preserved the β-O-4 structure of lignin during ACG pretreatment through α-etherification and γ-esterification. 31P NMR results showed that WSL has more aliphatic hydroxyl groups, resulting in increased water solubility, whereas WIL exhibited a higher amount of phenolic hydroxyl groups, contributing to the increased in vitro antioxidant properties. WSL contained significant proportion of p-coumaric acid glycerides and demonstrated low cytotoxicity along with a favorable cellular antioxidant capacity (CAA). HPLC-MS analysis revealed that the GG was a mixture of 56.44% glyceryl xylosides and 36.49% glyceryl glucosides, which displayed a superior moisturising capacity compared to commercial humectants such as hyaluronic acid (HA) and α-glyceryl glucosides (αGG). Overall, this study establishes a foundation for the extraction of value-adding bioactive compounds from acid-catalysed glycerol pretreatment hydrolysate, supporting the implementation of ACG techniques in biorefineries.