Abstract
Using an EDC/NHS conjugation method, chitosan was chemically modified to incorporate a photosensitive alpha-cyano-4-hydroxycinnamic acid moiety with various degrees of substitutions. The chitosan alpha-cyano-4-hydroxycinnamate was fully characterized by FTIR, H-1 NMR and UV-vis spectra. Lipase from Candida rugosa was entrapped in the modified photo-crosslinkable chitosan membranes. Crosslinking was carried Out by irradiation in the ultraviolet region. The activities of free and immobilized lipase have been studied The efficiency of the immobilization was evaluated by examining the relative enzymatic activity of free enzyme before and after the immobilization of lipase. The obtained Values were found to reach 98.6%, The results showed that the optimum temperature of immobilized lipase was 40 degrees C, which was identical to that of the free enzyme, and the immobilized lipase exhibited a higher relative activity than that of free lipase over 40 degrees C. The optimal pH for immobilized lipase was 8.0, which was higher than that of the free lipase (pH 7.5), and the immobilization resulted in stabilization of enzyme Over a broader pH range. The kinetic constant value (K-m) of immobilized lipase was 1.332 mg ml(-1) (1.50 x 10(-3) M), which was higher than that of free lipase. On the other hand, the activity of immobilized lipase decreased slowly against time when compared to that of the free lipase, and could retain 75.5% residual activity after 6 consecutive cycles. (C) 2009 Elsevier B.V. All rights reserved.