Microbial cellulases immobilized in biopolymer/silica matrices used as enzyme release systems

Abstract

Trichoderma viride CMGB 1 cellulases were immobilized by entrapment in silica gels (by 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 as cosolvents in a two step sol-gel synthesis. Combined alginate/silica matrices resulted by mixing silica sol with sodium alginate or by coating alginate beads with a silica shell. The partial confinement of ethylene glycol in the matrix with consequences on biocatalytic activity was investigated using SEM-EDAX, thermal analysis and FT-IR spectroscopy. 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 1.5-4.5 times higher compared to classical sol-gel methods that use EtOH. The characterization of the gels by microscopic and spectrophotometric analyzes 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-solvent. The new developed gels showed good cellulase release properties at acidic pH, comparable to those based on THEOS and alginate. The microbial cellulases immobilized in the matrices obtained and characterized in this work can operate as efficient systems for releasing enzymes, in acidic pH conditions, as feed additives.