Improving enzymatic hydrolysis of sunflower straw pretreated by deep eutectic solvent with different carboxylic acids as hydrogen bond donors

Here, sunflower straw (SS) (Helianthus annuus L.) was pretreated by deep eutectic solvent (DES) composed of choline chloride and different carboxylic acids to improve its enzymatic hydrolysis. The results showed that there were significantly negative correlations between the pKa of carboxylic acid with the delignification and xylan removal during pretreatment, where Y-(delignification)= 10.34 xX((pKa))+ 51.92 (R-2 =0.71) and Y-(xylan removal)= 17.62 xX((pKa))+ 77.13 (R-2 =0.78). The accessibility and crystallinity were increased from 60.2 mg/g to 256.4 mg/g and from 43.2% to 55.7%, respectively, which was ascribed to oxalic acid (OA) with the lowest pKa. Finally, the reduced sugar yield was extremely enhanced from 32.6% to 58.2% (Pretreatment condition: 160 degrees C, 10 min, and a solid-liquid mass ratio of 1:10). According to the condition optimization of DESOA pretreatment, the highest reducing sugar yield (63.5%) of SS was conditions of 160 degrees C, 12 min, and a solid-liquid mass ratio of 1:14. Obviously, an efficient DESOA pretreatment method was established to enhance the enzymatic hydrolysis efficiency of SS.