Enhancement of the Catalytic Performance and Operational Stability of Sol-Gel-Entrapped Cellulase by Tailoring the Matrix Structure and Properties

Abstract

Commercial cellulase Cellic CTec2 was immobilized by the entrapment technique in sol–gel matrices, and sol–gel entrapment with deposition onto magnetic nanoparticles, using binary or ternary systems of silane precursors with alkyl- or aryl-trimethoxysilanes, at different molar ratios. Appropriate tailoring of the sol–gel matrix allowed for the enhancement of the catalytic efficiency of the cellulase biocatalyst, which was then evaluated in the hydrolysis reaction of Avicel microcrystalline cellulose. A correlation between the catalytic activity with the properties of the sol–gel matrix of the nanobiocatalysts was observed using several characterization methods: scanning electron microscopy (SEM), fluorescence microscopy (FM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA/DTA). The homogeneous distribution of the enzymes in the sol–gel matrix and the mass loss profile as a function of temperature were highlighted. The influence of temperature and pH of the reaction medium on the catalytic performance of the nanobiocatalysts as well as the operational stability under optimized reaction conditions were also investigated; the immobilized biocatalysts proved their superiority in comparison to the native cellulase. The magnetic cellulase biocatalyst with the highest efficiency was reused in seven successive batch hydrolysis cycles of microcrystalline cellulose with remanent activity values that were over 40%, thus we obtained promising results for scaling-up the process.

Immobilization of Cellulolytic Enzymes in Accurel® MP1000

“…Thus, the enzymes present in the enzymatic extract ThI14-12 probably interacted more efficiently with the support, where more active conformations were generated for all enzymes, besides having been immobilized in a protein concentration that perhaps did not generate saturation of the support to the point of causing impediment or restriction of access of the enzymes to the substrate. These results are in line with several works reported in the literature for the immobilization of cellulases, where various immobilization techniques, such as covalent bonds, entrapment, and CLEA, are important to improve activity retention and enzyme activity [31,35,37,[40][41][42]. However, this is the first work where complex extracts are immobilized using a hydrophobic adsorption methodology on Accurel ® MP1000, a versatile support that is able to promote different hosting and adsorption interactions on its surface.…”

“…The commercial Celluclast ® 1.5 L cocktail is known to offer a different amount among these three enzymes, where it is more enriched with endoglucanases, such as CMCase and FPase, which are enzymes vital for the access of cellulose fibers that are highly recalcitrant, crystalline, and branched biopolymers [21]. Therefore, in order to achieve successful hydrolysis and to maximize the obtainment of oligosaccharides and cellobiose, endoglucanases are key proteins in this process, in addition to the various accessory proteins already reported [30,31]. In this sense, β-glucosidase is, in fact, activated in high concentrations of cellobiose, generating glucose as the final product.…”