Sustainable coproduction of xylooligosaccharide, single-cell protein and lignin-adsorbent through whole components’ utilization of sugarcane bagasse with high solid loading

Abstract

Free-waste biorefining of lignocellulosic biomass is environmentally friendly and accelerates the achievement of carbon neutrality. Here, we developed a sequential process of biorefining using a high solid loading of sugarcane bagasse (SB) as feedstock to coproduce xylooligosaccharide, glucose and xylose for the first time, including a three-step chemical pretreatment with a combination of diluted potassium hydroxide and phosphoric acid, followed by hydrolysis with recombinant endo-xylanase from Pichia pastoris and cellulase and xylanase from Penicillium oxalicum. The novel process achieved a maximum xylooligosaccharide yield of 5.59 g/100 g SB, comprising 77.1 % xylobiose, 18.5 % xylotriose and 4.4 % xylotetraose, a glucose yield of 32.96 g/100 g SB and a xylose yield of 7.68 g/100 g SB. The obtained glucose and xylose were used for the cultivation of Candida utilis, resulting in 13.20 g single-cell protein/100 g SB, 56.5 % of which was crude protein. Lignin residues were precipitated from the generated waste liquids by adjusting the pH, with a recovery extent of 94.15 %, used as lignin-adsorbent. The lignin-adsorbent could efficiently adsorb the dyes Acid Black 1, Direct Orange S and Procion Red MX-5B, with decolorization extents of 92.33 %, 93.00 % and 65.46 %, respectively. The final supernatant rich in phosphorus and potassium could be used as the feedstock of liquid fertilizer to nourish plants. This explored strategy provides an alternative option to utilize all components from SB that is eco-friendly.