Total Utilization of Components Contained in Coconut Husk by Microwave-Assisted Thermal Hydrolysis and Deep Eutectic Solvent Treatment

Abstract Microwave-assisted thermal hydrolysis treatment (MW: 150 W for 0–10 min) was used to obtain water-soluble and ethanol-soluble antioxidants from coconut husk (CH). The water extract with a maximum amount of phenolic compounds, i.e. 57.3 mg-catechin equiv./g-dry treated CH, was obtained from treated CH at 150 W for 10 min. Next, to efficiently utilize the lignin and cellulose in CH, a comprehensive utilization system that includes deep eutectic solvent (DES) treatment, separation, enzymatic saccharification, and acetone extraction has been developed. The solid residue with a cellulose-rich residue fraction was obtained by effectively removing lignin and hemicellulose via DES treatment. After 0.5 h at 150 °C, the solid residue had a cellulose ratio of more than 40% and it was used as a substrate of enzymatic saccharification. The saccharification ratio raised considerably with the DES treatment; at a saccharification time of 24 h with a maximum value of 2.11 g/L, which was 6.8 times higher than untreated CH. Since the precipitate contains low-molecular-weight lignin that was isolated from the supernatant of the DES-treated CH, it can be utilized as a raw material of epoxy resin and curing agent. Graphical Abstract