Cross-linking of lipases adsorbed on hydrophobic supports: Highly selective hydrolysis of fish oil catalyzed by RML

Organic cosolvents may improve the properties of lipases (e.g., selectivity); however, organic cosolvents also promote the desorption of the enzyme from its hydrophobic supports. In this study, adsorbed lipase molecules were cross-linked with polyfunctional polymers, such as aldehyde-dextrans, to prevent this desorption. The desorption of adsorbed lipases was greatly reduced by optimizing the polymer size, polymer/lipase ratio, and cross-linking time. More than 95% of cross-linked, immobilized Rhizomucor miehei lipase (RML) remained adsorbed on the support after washing with cosolvents or detergents. This new, immobilized RML preparation mediated the hydrolysis of sardine oil in the presence of organic cosolvents. The presence of cosolvents promoted small losses of hydrolytic activity. Interestingly, however, 50% 2-propanol also promoted increased selectivity in the release of eicosapentaenoic acid (EPA) in relation to docosahexaenoic acid (DHA). An EPA/DHA ratio of 4:1 in the absence of 2-propanol was increased to a ratio of 22:1 in the presence of 2-propanol. The new RML derivatives were relatively stable under the selected reaction conditions. Their overall half-life was 100 h, but, in a second inactivation phase (below 60% of remaining activity), it took 600 h to reach 30% of their remaining activity.