Coupling chemical modification and immobilization of cellulase improves thermal stability and low-melting mixture solvent tolerance for in situ saccharification of bagasse

In situ saccharification of lignocellulosic biomass in low-melting mixture solvents (LoMMSs) is a promising approach for biorefinery. In this study, chemical modification of cellulase coupled with immobilization was designed to improve thermal stability and LoMMS tolerance of cellulase for in situ saccharification. Cellulase was firstly chemically modified with succinic anhydride and ethylenediamine respectively to form succinylated cellulase (S-Ce) and aminated cellulase (A-Ce), then the modified cellulases were immobilized with amino-functionalized metal-organic frameworks to establish ZIF-8/A immobilized A-Ce and S-Ce. Circular dichroism, fluorescence measurements, X-ray diffraction, fourier transform infrared spectra and scanning electron microscopy were applied to characterize the modified cellulase or immobilization carrier. ZIF-8/A immobilized A-Ce presented desired thermal stability and LoMMS tolerance. Reducing sugar yields via ZIF-8/A immobilized A-Ce during in situ saccharification of bagasse maintained stably till Bet/AA concentration reached 50%, and declined relatively slowly compared with free or other immobilized cellulase when Bet/AA concentration further increased to 90%. In situ saccharification of bagasse via ZIF-8/A immobilized A-Ce in concentrated Bet/AA (50%) can be operated at a wide temperature range (50–60 °C). The corresponding reducing sugar yield with ZIF-8/A immobilized A-Ce was 58% higher than that with free cellulase in 50% Bet/AA at 60 °C.