Optimization of lipase entrapment in Ca-alginate gel beads

Lipase from Candida rugosa was entrapped by drop-wise addition of an aqueous mixture of sodium alginate and the biocatalyst to a hardening solution of a Ca2+ salt. Effects of immobilization conditions such as alginate concentration, CaCl2 concentration, ratio by weight of enzyme to alginate (E/A) and bead size on loading efficiency (percent of total enzyme entrapped) and immobilization yield (specific activity ratio of entrapped lipase to free lipase) were investigated. An increase in alginate concentration raised loading efficiency, but decreased immobilization yield. CaCl2 concentration was expected to have a similar effect on loading efficiency and immobilization yield, but the effect was small in the tested range of 50–300 mM. With increasing bead size, immobilization yield decreased due to mass transfer resistance, but loading efficiency was unchanged. In order to prevent enzyme from leaking out of the gel beads, beads were coated with chitosan and silicate. Compared to non-coated beads, coated alginate beads showed the higher re-usability, illustrating the effectiveness of the coating method. When coated with silicate, lipase-entrapped beads retained the highest catalytic activity.