Enhancing the biorefinery of chestnut burrs. Part I. Study of the pretreatment with choline chloride urea diluted deep eutectic solvent

Chestnut burrs (CB) are agro-industrial wastes produced in large amounts during chestnut processing. Despite their high value composition, this type of biomass has been scarcely studied, becoming an important material to be valorized. In this work, a green technology based on the use of diluted choline chloride urea (ChCl:U) deep eutectic solvent (DES) was postulated to deconstruct the lignocellulosic structure. The pretreatment was evaluated using untreated CB and CB previously processed (washed CB or the solid residue obtained after prehydrolysis). Following a biorefinery concept, the samples obtained in this work will be further enzymatically hydrolyzed in Part II to reach fermentable sugars-containing solutions. Several operational parameters such as time (4, 8 and 16 h), temperature (60, 80, 100 and 120 °C), and liquid-solid ratio (LSR) (10:1, 15:1 and 20:1) were studied to improve CB deconstruction. Physicochemical transformations were investigated by ATR-FTIR and SEM analysis. The best delignification rate (∼40%) was achieved applying the DES pretreatment in untreated CB at 100 °C for 16 h and 20:1 (w/w) LSR, being corroborated by physicochemical changes observed by FTIR and SEM. •Chestnut burrs (CB) are produced in large amounts during chestnut processing.•DES pretreatment delignifies aprox. 40% CB enriching the polysaccharides content.•ATR-FTIR and SEM corroborate physicochemical changes after pretreatment.•DES in prepared CB increase the total polysaccharide content.