Harnessing deep eutectic solvent for enhanced inulinase production from agricultural via submerged fermentation with Aspergillus niger

This study aimed to enhance inulinase production from agricultural biomass pretreated with deep eutectic solvents (DES) using Aspergillus niger A42 (ATCC 204447). Barley husk (BH), wheat bran (WB), and oat husk (OH) were selected as substrates and were pretreated using different molar ratios of choline chloride: glycerol (ChCl: Gly) and choline chloride: acetic acid (ChCl: AA). DES pretreatment was followed by dilute sulfuric acid hydrolysis. The fermentable sugar content (FSC), sugar profiles, and inhibitory components in the hydrolysates were analyzed. DES pretreatment improved the FSC in all substrates, with wheat bran showing the highest FSC of 72.54 g/mL. Considering the fermentable sugar contents, ChCl: Gly (1:2) was selected as the most suitable DES. The analysis of biomass composition after pretreatment indicated a reduction in extractives and lignin, along with an increase in cellulose content. Subsequently, inulinase fermentation using Aspergillus niger A42 has demonstrated that DES-pretreated wheat bran was the most effective substrate, yielding 416.05 U/mL inulinase activity (Iase) and 486.22 U/mL invertase-type (Sase) activity. The enzyme solution was partially purified via Spin-X UF membranes (50 kDa cut-off), resulting in Iase activity of 769.93 U/mL and Sase activity of 566.69 U/ mL. The purification coefficients were 1.88 and 0.92 for inulinase and invertase-type activity, respectively. In conclusion, DES pretreatment was successfully applied to produce inulinase enzyme from BH, WB, and OH. Among the materials studied, WB emerged as the most suitable biomass for producing inulinase from Aspergillus niger A42.