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.
Highlights
The global production of oats in the crop year 2018/2019 was 22 million metric tons, with the European Union being the leading producer [1]
Lignocellulosic materials are rich in polysaccharides, namely cellulose and hemicellulose, which can be enzymatically hydrolyzed into monomeric sugars for further use, such as microbial conversion into biofuels and biochemicals [3]
A first set of parameters for acid-catalyzed ethanol organosolv pretreatment of oat husks was found in this study
Summary
The global production of oats in the crop year 2018/2019 was 22 million metric tons, with the European Union being the leading producer [1]. Lignocellulosic materials are rich in polysaccharides, namely cellulose and hemicellulose, which can be enzymatically hydrolyzed into monomeric sugars for further use, such as microbial conversion into biofuels and biochemicals [3]. The recalcitrance of lignocellulosic materials to the direct action of enzymes, and the consequent need for a pretreatment step to deconstruct the material and grant access to the polysaccharides, is well documented in the literature [4,5,6]. The different pretreatment steps have dissimilar impacts on lignocellulosic structures, mostly regarding the fraction (cellulose, hemicellulose, and lignin) that is affected, that is, which fraction is being hydrolyzed and dissolved [6].
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