Holistic lignocellulosic biorefinery approach for co-production of L-lactic acid, flavonoids, and lignin from Euryale ferox seed shell feedstock

Euryale ferox seed shell (EFSS) is an agricultural waste biomass with abundant cellulose, hemicellulose, lignin and extractives. However, the complete valorization of EFSS to valuable products is still challenging. Herein, a holistic lignocellulosic biorefinery approach was proposed, employing a novel two-stage deep eutectic solvent (DES) treatment for efficient fractionation of EFSS. Firstly, 0.18 g/g dry matter (DM) of flavonoids were extracted from raw EFSS by choline chloride/lactic acid ([ChCl][LA]) DES combined with ultrasonic treatment under optimized conditions (water content of 30 %, L/S ratio of 25:1, 180 W, 70 °C, and 120 min), and the extracted flavonoids demonstrated multiple antioxidant activities. Meanwhile, the considerable cellulose, xylan and lignin were retained in the solids, with recovery yields of 84.9 %, 89.0 % and 89.8 %, respectively. Then, lignin (0.31 g/g DM) was isolated from the filtered solids by [ChCl][LA] treatment at 110 °C for 90 min. The retained cellulose and xylan in the residue were utilized through simultaneous saccharification and fermentation (SSF) by Bacillus coagulans , achieving 88.3 g/L of L -lactic acid from EFSS biomass with a yield of 0.25 g/g. This study provides an innovative fractionation process for efficient cascade valorization of EFSS into valuable products. • A holistic lignocellulosic·biorefinery approach·was used for valorization of EFSS. • Co-production of flavonoids, lignin and L -lactic acid·was achieved from·EFSS. • 0.18, 0.31 and 0.25 g/g DM of flavonoids, lignin and L -lactic acid were produced.