Effect of deacetylation degree of chitosan on rheological properties and physical chemical characteristics of genipin-crosslinked chitosan beads

The effect of the degree of deacetylation (DD) on the characteristics of the support matrix formed through chitosan (CH) and genipin (GE) crosslinking was investigated by using CH with DD of 83, 94 and 96%. The rheological properties of CH dispersions were determined in order to study the influence of DD on the CH viscosity, gel network structures and gelation temperature (Tgel). The CH exhibited the shear-thinning behavior of pseudoplastic fluids. Tgel decreased with the increase of DD and the sol-gel transition temperature of CH-83, CH-94 and CH-96 were 75, 30 and 25 degrees C, respectively. The magnitude of viscous modulus (G) was higher than the elastic modulus (G'), revealing the formation of a weak gel structure. The CH dispersions have been used in the preparation of beads and then crosslinked with GE to form support matrices. Besides, to verify how it influences in a practical application, an enzymatic immobilization was carried out using a beta-D-galactosidase (BG) as a model, which could be advantageously employed to promote hydrolysis of lactose. Scanning Electron Microscope images showed biocatalysts with multiple porous compartments. Fourier Transform Infrared Spectroscopy (FTIR) analyses confirmed chemical and physical interactions between CH, GE and BG. Thermogravimetric analysis (TGA) demonstrated that the DD of CH had a positive influence in the thermal degradation behavior of the biocatalysts up to 200 degrees C, which represents the temperature range used in most enzymatic reactions (up to 100 degrees C) in the industrial scale applications.