Effects of preparative parameters on the properties of chitosan hydrogel beads containing Candida rugosa lipase

The influences of the pH, tripolyphosphate (TPP) concentration, and ionic strength of the gelling medium on the entrapment efficiency, release, and activity of lipase, in chitosan hydrogel beads were studied. A solution of Candida rugosa lipase was prepared in a 1.5% w/v chitosan and 1% (v/v) acetic acid medium, and dropped into a TPP solution. Release of lipase in pH 7.2 Tris buffer was monitored over 36 h using the micro BCA protein assay. The activity of the entrapped enzyme was assayed using the Sigma lipase activity method. Following preliminary studies, an experimental design was followed to develop mathematical models that describe bead characteristics as functions of the pH and the TPP concentration in the gelling medium. The pH and the TPP concentration each had an effect on the entrapment, retention, and activity of lipase. Entrapped lipase retained a high degree of activity in multiple reactions. The ionic strength, in the range studied, exerted a minimal effect on bead characteristics. Statistical analysis allowed optimization within the factor space with respect to maximizing the enzyme entrapment efficiency and activity, and also minimizing the amount released after 36 h in the Tris buffer. (C) 2003 Elsevier Ltd. All rights reserved.