Changing gel structure and immobilization conditions led to a significant improvement in the covalent multipoint attachment of chymotrypsin on chitosan. The use of sodium alginate, gelatin, or kappa-carrageenan, activation with glutaraldehyde, glycidol, or epichlorohydrin, and addition of microorganisms followed by cellular lysis allowed the modification of the gel structure. Immobilization yields, recovered activities, and stabilization factors at 55 and 65 degrees C were evaluated. Enzyme immobilization for 72 h at pH 10.05, 25 degrees C and reduction with NaBH 4 in chitosan 2.5%-carrageenan 2.5%, with addition of S. cerevisiae 5% and activation with epichlorohydrin led to the best derivative, which was 9900-fold more stable than the soluble enzyme. This support allowed an enzyme load up to 40 mg chymotrypsin x g gel (-1). The number of covalent bonds, formed by active groups in the support and lysine residues of the enzyme, can explain the obtained results. SEM images of the gel structures corroborate these conclusions.

This work aimed at the production of stabilized derivatives of Thermomyces lanuginosus lipase (TLL) by multipoint covalent immobilization of the enzyme on chitosan-based matrices. The resulting biocatalysts were tested for synthesis of biodiesel by ethanolysis of palm oil. Different hydrogels were prepared: chitosan alone and in polyelectrolyte complexes (PEC) with κ-carrageenan, gelatin, alginate, and polyvinyl alcohol (PVA). The obtained supports were chemically modified with 2,4,6-trinitrobenzene sulfonic acid (TNBS) to increase support hydrophobicity, followed by activation with different agents such as glycidol (GLY), epichlorohydrin (EPI), and glutaraldehyde (GLU). The chitosan-alginate hydrogel, chemically modified with TNBS, provided derivatives with higher apparent hydrolytic activity (HA(app)) and thermal stability, being up to 45-fold more stable than soluble lipase. The maximum load of immobilized enzyme was 17.5 mg g(-1) of gel for GLU, 7.76 mg g(-1) of gel for GLY, and 7.65 mg g(-1) of gel for EPI derivatives, the latter presenting the maximum apparent hydrolytic activity (364.8 IU g(-1) of gel). The three derivatives catalyzed conversion of palm oil to biodiesel, but chitosan-alginate-TNBS activated via GLY and EPI led to higher recovered activities of the enzyme. Thus, this is a more attractive option for both hydrolysis and transesterification of vegetable oils using immobilized TLL, although industrial application of this biocatalyst still demands further improvements in its half-life to make the enzymatic process economically attractive.

The aim of this paper was to evaluate different strategies of chitosan activation using cross-linking reagent like glycidol, epichlorohydrin, and glutaraldehyde for Thermomyces lanuginosus lipase (TLL) immobilization. Operational activity and stability by esterification of oleic acid with ethanol and thermal inactivation using these derivatives were investigated. Derivative obtained by sequentially activation with glycidol, ethylenediamine, and glutaraldehyde and subsequent TLL immobilization showed the best performance, with high hydrolytic activity value. Its stability was 15-fold higher than solubilized TLL in the evaluated inactivation conditions (60 °C, 25 mM sodium phosphate buffer pH 7). After 5 cycles of oleic acid esterification, only a few percentage of its conversion has reduced. On the other hand, glycidol-activated chitosan derivative showed very low hydrolytic activity value. Epichlorohydrin-activated chitosan derivative showed regular hydrolytic activity value. Both derivatives showed low immobilization yields. Operational stability of this last derivative was very low, where after the first cycle of oleic acid esterification, only 56% of its initial conversion was obtained. Graphical Abstract ᅟ.