Alkaline organosolv pretreatment of different sorghum stem parts for enhancing the total reducing sugar yields and p-coumaric acid release

Abstract

Background: The sorghum stem can be divided into the pith and rind parts with obvious differences in cell type and chemical composition, thus arising the different recalcitrance to enzyme hydrolysis and demand for different pretreatment conditions. The introduction of organic solvents in the pretreatment can reduce over-degradation of cellulose and hemicellulose, but significance of organic solvent addition in pretreatment of different parts of sorghum stem is still unclear. Valorization of each component is critical for economy of sorghum biorefinery. Therefore, in this study, NaOH-ethanol pretreatment condition for different parts of the sorghum stem was optimized to maximize p-coumaric acid release and total reducing sugar recovery. Result: Ethanol addition improved p-coumaric acid release and delignification efficiency, but significantly reduced hemicellulose deconstruction in NaOH-ethanol pretreatment. Optimization using the response surface methodology revealed that the pith, rind and whole stem require different NaOH-ethanol pretreatment conditions for maximal p-coumaric acid release and xylan preservation. By respective optimal NaOH-ethanol pretreatment, the p-coumaric acid release yields reached 94.07%, 97.24% and 95.05% from pith, rind and whole stem, which increased by 8.16%, 8.38% and 8.39% compared to those of NaOH-pretreated samples. The xylan recoveries of pith, rind and whole stem reached 76.80%, 88.46% and 85.01%, respectively, which increased by 47.75%, 15.11% and 35.97% compared to NaOH pretreatment. Adding xylanase significantly enhanced the enzymatic saccharification of pretreated residues. The total reducing sugar yields after respective optimal NaOH-ethanol pretreatment and enzymatic hydrolysis reached 84.06%, 82.29% and 84.09% for pith, rind and whole stem, respectively, which increased by 29.56%, 23.67% and 25.56% compared to those of NaOH-pretreated samples. Considering the separation cost of the different stem parts, whole sorghum stem can be directly used as feedstock in industrial biorefinery. Conclusion: These results indicated that NaOH-ethanol is effective for the efficient fractionation and pretreatment of sorghum biomass. This work will help to understand the differences of different parts of sorghum stem under NaOH-ethanol pretreatment, thereby improving the full-component utilization of sorghum stem.

Enhancing biomass conservation and enzymatic hydrolysis of sweet sorghum bagasse by combining pretreatment with ensiling and NaOH

“…In the present study, the morphology of SBB was significantly changed after combined pretreatment when compared to raw SBB. Similar results were also observed in a previous study reported by Li et al ( 2020 ). This morphological change is caused by the saponification reaction between NaOH and the intermolecular ester bond of lignin, which results in the removal of the surface lignin layer and the release of cellulose from the biomass matrix, exposing more of the internal structure and increasing the external area (Umagiliyage et al, 2015 ).…”

Alkali-Catalyzed Organosolv Pretreatment of Lignocellulose Enhances Enzymatic Hydrolysis and Results in Highly Antioxidative Lignin

“…5‑1h , S A1‑1h , and S A2–1h , dense holes and broken surfaces are noticed. Indeed, due to the removal of a large amount of lignin, alkali-catalyzed pretreatment results in structural changes on the biomass surface that facilitates enzyme erosion. , …”

“…Indeed, due to the removal of a large amount of lignin, alkali-catalyzed pretreatment results in structural changes on the biomass surface that facilitates enzyme erosion. 40,41 3.2.4. Enzymatic Hydrolysis.…”

Bringing Material Concepts into Conventional Biorefineries: Considerations of Sources, Preparations, and Applications of Lignin Nanomaterials

“…This requires innovation in technologies and the complete valorization of various feedstocks in an environmentally friendly manner. Biorefinery is of great importance for alleviating the shortage of industrial raw materials, and the overreliance on fossil resources as biomass resources are renewable, cheap, and widely accessible. − Lignocellulosic biomass, mainly consisting of cellulose (∼40%), hemicellulose (∼20%), and lignin (∼20%), is the most abundant biomass feedstock that can be converted to various products such as building materials, papers, biofuels, and biochemicals. − However, most conventional biorefining processes such as pulping and bioethanol industries focus on the use of carbohydrates (i.e., cellulose and hemicellulose). In contrast, lignin, a natural aromatic polymer, and one of the most attractive renewable precursors for smart material preparation, is not fully utilized. − Taking the bioethanol industry as an example, by 2022, about 62 million tons of lignin are predicted to be produced annually in the United States, and an increasing amount of extra lignin will be left after providing external energy by combustion. ,, Valorizing lignin is meant to enhance the profitability of conventional biofuel and biochemical scenarios, thus enhancing the economy of biorefining …”