Microbial cellulases immobilized in biopolymer/silica matrices used as enzyme release systems
Trichoderma viride CMGB 1 cellulases were immobilized by entrapment in silica gels (by the sol-gel method), alginate biopolymers and hybrid alginate/silica materials. Tetramethoxysilane (TMOS), tetraethoxysilane (TEOS) and tetrakis (2-hydroxyethyl) orthosilicate (THEOS) were used as organoalkoxysilane precursors, and ethanol or ethylene glycol (EG) as cosolvents in a two-step sol-gel synthesis. Combined alginate/silica matrices were obtained by mixing the silica sol with sodium alginate or by coating alginate beads with a silica shell. A partial confinement of ethylene glycol in the matrix and its consequences on biocatalytic activity were investigated using scanning electron microscopy-Energy Dispersive X-Ray Analysis (SEM-EDAX), Fourier-transform infrared spectroscopy (FT-IR). The efficiency of the enzyme-matrix biomaterials was tested in controlled enzyme release experiments. The sol-gel method developed using EG as a co-solvent allowed cellulase immobilization yields that were 1.5–4.5 times higher when compared to classical sol-gel methods that use EtOH. Characterization of the gels by microscopic and spectrophotometric analyses showed that there are similarities between the structure of the gels based on THEOS and those developed by us from TEOS, TMOS and EG as co-solvents. The gels developed here showed good cellulase release properties at acidic pH, comparable to those based on THEOS and alginate. Microbial cellulases immobilized in the matrices obtained here and characterized in this work can operate as efficient systems for releasing enzymes, at acidic pH conditions, as feed additives.
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