Fate of p-hydroxycinnamates and structural characteristics of residual hemicelluloses and lignin during alkaline-sulfite chemithermomechanical pretreatment of sugarcane bagasse

• Published in: Biotechnology for biofuels Vol. 11; no. 1; p. 153
• Main Authors: Reinoso, Felipe A. M., Rencoret, Jorge, Gutiérrez, Ana, Milagres, Adriane M. F., del Río, José C., Ferraz, André
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 05.06.2018; BioMed Central; BMC
• Subjects: Alternative energy sources; Bagasse; Biodiesel fuels; Biomass; Bioprocessing; Biorefineries; biorefining; Cellulase; Cellulose; enzymatic hydrolysis; Enzymes; Ethanol; feedstocks; Fermentation; Grasses; Hemicellulose; Hemicelluloses; Hydrolysis; Lignin; Lignocellulose; Linkages; Liquor; moieties; Morphology; Multivariate analysis; NMR; Nuclear magnetic resonance; nuclear magnetic resonance spectroscopy; Organic chemistry; p-Hydroxycinnamates; Physical characteristics; physicochemical properties; Physiological aspects; Polysaccharides; Pretreatment; Properties; Pulp & paper industry; Recalcitrance; Refining; Saccharides; Saccharification; saponification; Solids; Substrates; Sugarcane; sugarcane bagasse; Sulfite; Xylan; Brazil; Spain; Lignin; Hemicelluloses; Recalcitrance; Biorefinery; Grasses; Pretreatment; Alkaline-sulfite; Sugarcane; p-Hydroxycinnamates
• ISSN: 1754-6834; 1754-6834; 2731-3654
• DOI: 10.1186/s13068-018-1155-3

Preparing multiple products from lignocellulosic biomass feedstock enhances the profit and sustainability of future biorefineries. Grasses are suitable feedstocks for biorefineries as they permit a variety of possible by-products due to their particular chemical characteristics and morphology. Elucidating the fate of -hydroxycinnamates (ferulates-FAs and -coumarates- CAs) and major structural components during bioprocessing helps to discriminate the sources of recalcitrance in grasses and paves the way for the recovery of -hydroxycinnamates, which have multiple applications. To address these subjects, we assessed sugarcane bagasse biorefining under alkaline-sulfite chemithermomechanical (AS-CTM) pretreatment and enzymatic saccharification. The mass balances of the major bagasse components were combined with 2D-NMR structural evaluation of process solids to advance our understanding of sugarcane bagasse changes during biorefining. AS-CTM pretreatment provided a high yield and thoroughly digestible substrates. The pretreated material was depleted in acetyl groups, but retained 62 and 79% of the original lignin and xylan, respectively. Forty percent of the total FAs and CAs were also retained in pretreated material. After pretreatment and enzymatic hydrolysis, the residual solids contained mostly lignin and ester-linked CAs, with minor amounts of FAs and non-digested polysaccharides. Saponification of the residual solids, at a higher alkali load, cleaved all the ester linkages in the CAs; nevertheless, a significant fraction of the CAs remained attached to the saponified solids, probably to lignin, through 4- ether-linkages. AS-CTM pretreatment provided soundly digestible substrates, which retain substantial amounts of xylans and lignin. Acetyl groups were depleted, but 40% of the total FAs and CAs remained in pretreated material. Ester-linked CAs detected in pretreated material also resisted to the enzymatic hydrolysis step. Only a more severe saponification reaction cleaved ester linkages of CAs from residual solids; nevertheless, CAs remained attached to the core lignin through 4- ether-linkages, suggesting the occurrence of an alkali-stable fraction of CAs in sugarcane bagasse.