Biorefining Oat Husks into High-Quality Lignin and Enzymatically Digestible Cellulose with Acid-Catalyzed Ethanol Organosolv Pretreatment

Abstract

Oat husks are low-value lignocellulosic residues of oat processing that carry an environmental impact. Their polymers (cellulose, hemicellulose, and lignin) can be converted into a wide variety of value-added products; however, efficient pretreatment methods are needed that allow their fine separation for further tailored valorization. This study pioneered the use of milling-free and low acid-catalyzed ethanol organosolv for the delignification of oat husks, allowing their conversion into three high-quality streams, namely, glucan-rich, lignin-rich, and hemicellulosic compound-rich streams. Temperature, retention time, and solid-to-liquid ratio were found to impact the delignification of oat husks when using a one-factor-at-a-time strategy. The ideal conditions that were found (210 °C, 90 min, and solid-to-liquid ratio of 1:2) culminated into glucan and lignin fractions containing 74.5% ± 11.4% glucan and 74.9% ± 7.6% lignin, respectively. These high-purity lignin fractions open the possibility for higher value applications by lignin, potentially impacting the feasibility of second generation biorefineries. The glucan fraction showed 90% digestibility after 48 h of hydrolysis with 10 filter paper units of enzyme cocktail per gram of glucan. Considering the absence of size reduction and high solid loading, together with the quality of the obtained streams, organosolv pretreatment could be a potential strategy for the valorization of oat lignocellulosic residues.

Recovery of High Purity Lignin and Digestible Cellulose from Oil Palm Empty Fruit Bunch Using Low Acid-Catalyzed Organosolv Pretreatment

“…Moreover, information about the influence of pretreatment parameters on lignin recovery and purity following organosolv pretreatment is still scarce in the literature, and it is common to all lignocellulosic substrates studied [28]. A recent study has shown that organosolv pretreatment conditions influence the recovery and purity of lignin from oat husks [35]. Therefore, the aim of the present study was to study the effect of acid-catalyzed ethanol organosolv pretreatment on the delignification of OPEFB.…”

The Food–Materials Nexus: Next Generation Bioplastics and Advanced Materials from Agri‐Food Residues

“…[ 25 ] The limonene fraction can be valorized as monomer or monomer precursor, as discussed in Sections 3.3.1–3.3.2. Alternatively, other polysaccharide‐rich waste streams from FLW, which can be processed in sugar hydrolysates, can be used to produce 2G ethanol, e.g., pulping residues from bagasse, [ 422 ] crop husks, [ 423 ] or other agricultural residues. [ 424 ] In general, lignocelluloses, such as straw, are liquefied by enzymes to produce soluble sugar, a lignin fraction, and nonsoluble residues, with the possibility for the latter two to be burnt for energy generation or for valorizing the isolation of biocolloids (Section 3.1) or biopolymers (Section 3.2).…”

Agro-Food Residues and Bioethanol Potential: A Study for a Specific Area

“…Unfortunately, lignin is nonfermentable by microorganisms, insoluble, and recalcitrant to biochemical and chemical treatments. Therefore, lignin cannot be considered for bioethanol production but it could be utilized for heat or electricity production contributing to the sustainability of the entire process [21,26,68,69].…”

“…Unfortunately, these potentially convertible biomasses are heterogeneous in composition and origin and consequently require the application of chemical-physical treatments aimed at hydrolyzing plant polysaccharides into sugars to be fermented by microorganisms [7,15,22,23]. These procedures are strongly dependent on the chemical and physical nature of the substrates [24][25][26]. Many studies have been developed in the past about the possible exploitation of specific agri-cultural biomasses or wastes from industrial processes at the national or world level (see as examples: [21,[27][28][29][30]), and in general, the amounts of agricultural wastes in Europe could be considerable [31][32][33].…”