Use of chitosan heterofunctionality for enzyme immobilization: ß-galactosidase immobilization for galacto-oligosaccharide synthesis.

Chitosan partially functionalized with aldehyde groups was used for enzyme immobilization, favoring first the enzyme adsorption through its amino groups and then the covalent bonding of the adsorbed catalyst through the aldehyde groups of the support. Using this strategy, immobilized A. oryzae ß-galactosidase had a better performance than when only the aldehyde groups were used. The performance was further improved by modifying the support aldehyde group density to 200 µmoles⋅g-1. The biocatalyst under optimized immobilization conditions had 2951 IU⋅g-1 and half-life of 46.3 min at 60 °C, while its agarose counterpart had 2294 IU⋅g-1 and half-life of 59.5 min. Both biocatalysts were applied in galacto-oligosaccharide synthesis. After 10 sequential batches, the cumulative productivity (gGOS⋅h-1ˑgprotein-1) obtained with the chitosan and the agarose biocatalysts were 4.7 and 4.0 times the value when soluble enzyme was used respectively. This methodology had not been reported previously with chitosan, showing the high versatility of this low cost carrier and its high potential for enzyme immobilization.