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

 Biomass & Bioenergy, 173, 106786, 2023

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.

Enhancing the saccharification of pretreated chestnut burrs to produce bacteriocins

 Journal of Biotechnology, 329, 13-20

The present study aims to valorize chestnut burrs, an important lignocellulosic waste, through a biorefinery concept. A solid residue rich in glucan (41.36 ± 0.59 %) and lignin (39.06 ± 0.01 %) obtained from a previous process of pre-hydrolysis was subjected to four treatments with water or NaOH to enhance enzymatic hydrolysis. Saccharification was performed using different ratios of commercial cellulases and β-glucosidases and at controlled pH 4.8 or 6.0 (with citrate buffer) or uncontrolled pH. Carbohydrate-rich solutions with or without nutrients were used to produce bacteriocins by Lactobacillus plantarum CECT 211. The use of NaOH at high temperatures (120 and 130 °C) was the most suitable treatment to improve saccharification. Regarding the production of bacteriocins, the best result was obtained using the enzymatic solution obtained at controlled pH 6.0, supplemented with MRS broth nutrients (except glucose). Thus, the concentrations of bacteriocins obtained in this culture medium (9.21 BU/mL) was 1.22 and 1.98 times higher than those obtained in the nutrient supplemented medium buffered at pH 4.8 (7.56 BU/mL) and in the commercial MRS broth (4.65 BU/mL), respectively. These results highlight the feasibility of the technology developed in this work.