Valorization of agricultural residue for the production of fructose using fungal inulinase from Talaromyces domesticus ITCC 9483

Fungal inulinase hydrolyzes inulin to fructose, a commercially important intermediate with a wide range of applications in various industries. However, its industrial utilization is limited due to high cost of production and processing. Therefore, the present study reports the valorization of low-cost agricultural residues (AR) as an alternative substrate for inulinase production and its application in generation of fructose. In the study, an inulinase producing fungal strain was identified as Talaromyces domesticus ITCC 9483 based on preliminary and secondary screening. Further, various low-cost AR were screened for efficient inulinase production. Amongst these substrates, rice husk (RH) supported the highest enzymatic activity and was utilized as a major component for medium optimization in the presence of inulin as an inducer. It resulted in 2.02-fold increase in inulinase activity from 8.34 ± 1.45 U/mL to 16.86 ± 1.29 U/mL. The inulinase was purified resulting in 5.52-fold purification and a molecular mass of ~ 45–50 kDa. The zymographic analysis confirmed inulinase via distinct red band on native gel. The purified inulinase exhibited maximum stability at pH 5.0 and 50 °C after 24-hours of incubation, with K m 0.83 ± 0.19 mM and V max 4.58 ± 0.48 µmol/min. The structural characteristics were evaluated using UV spectrum, FTIR and XRD. The optimized inulinase was further employed for valorization of AR generating maximum reducing sugar yield of 2.14, 0.96 and 0.34 mg/mL from WB, SR and wheat straw (WS). The high-performance liquid chromatography (HPLC) confirmed fructose as primary hydrolysis product with concentrations of 47.94, 38.91 and 28.99%. Overall, the study established T. domesticus ITCC 9483 as a potent producer of inulinase capable of valorizing low-cost AR into value-added fructose through enzymatic bioprocessing. The generated fructose can further serve as a significant intermediate for application in biorefinery, food and pharmaceutical industries.