Preparation and characterization of chitosan-containing hydrogel beads for immobilization of Candida rugosa lipase with high retention of its hydrolytic activity

Chitosan, a natural, non-toxic, biodegradable polysaccharide has received attention recently for use in the entrapment of enzymes and cells. Chitosan refers to a family of polymers with different intrinsic properties, such as different molecular weights and degrees of deacetylation. Chitosan with different molecular weights and degrees of deacetylation was used to entrap lipase, a unique enzyme that has numerous pharmaceutical and industrial applications.; The goals of this dissertation research were to investigate the effects of the molecular weight and degree of deacetylation of chitosan, and the influence of preparation parameters, such as the pH of the gelling medium, the counterion (tripolyphosphate) concentration, and the ionic strength of the tripolyphosphate solution on the lipase entrapment efficiency of the beads, the release of lipase from the beads, the activity of lipase when loaded in the beads, the effect of freeze drying on lipase, and characteristics of the beads before and after freeze drying.; The results indicate that chitosan with high molecular weight and degree of deacetylation can improve lipase loading, and lessen the release of the entrapped lipase. On the basis of an amount of free enzyme equivalent to the lipase entrapped, about 50% retention of activity was seen with lipase entrapped in these beads. The friability results indicate that the beads are rugged enough for use in different applications. The pH of the gelling medium and the counterion concentration were found to have significant effects on the lipase entrapment efficiency, the release of lipase from the beads, the activity of lipase when loaded in the beads, as well as characteristics of the beads. On the contrary, ionic strength did not play an important role on the hydrogel beads properties. Entrapment efficiency and hydrolytic activity were found to be maximum when the gelling medium pH was 7.0. The enzymatic activity of the lipase-loaded chitosan beads prepared at pH 7.0 was 70% of the activity of a comparable mass of free lipase. A 0.5% w/v tripolyphosphate concentration in a pH 7.0 solution would provide beads with desirable qualities.