Enhancing the Stability of Fungal Lipases by Immobilization onto Accurel MP 1000 Support and Additional Glutaraldehyde Crosslinking

Commercial fungal lipases from <i>Rhizopus oryzae</i>, <i>Rhizopus niveus</i>, <i>Aspergillus niger</i>, <i>Rhizomucor miehei</i>, and <i>Candida rugosa</i> were immobilized via physical adsorption onto Accurel MP 1000, a hydrophobic polypropylene support. The effects of enzyme concentration, pH, temperature, and glutaraldehyde post-treatment were systematically evaluated. Immobilization generally enhanced enzyme stability, which was further improved in several cases by glutaraldehyde crosslinking. The immobilized preparations retained over 50% of their initial activity for 3-6 cycles, and 7-10 cycles following glutaraldehyde treatment. While soluble enzymes lost nearly all activity within three months at 5 °C and 25 °C and retained only 5-20% at -20 °C, the immobilized forms preserved 50-100% of their activity under all storage conditions tested. Immobilized lipases also exhibited improved thermal stability at 60 °C by general increments between 1.3 and 1.8 times compared to soluble lipases. Increased tolerance to pH fluctuations was observed in most immobilized enzymes, particularly from <i>R. oryzae</i>, <i>R. niveus</i>, <i>R. miehei</i>, and <i>C. rugosa</i>. Organic solvent tolerance of the immobilized enzymes showed highest stability in hexane (66-100% residual activity after 4 h incubation). Glutaraldehyde treatment affected solvent stability of immobilized lipases in enzyme and solvent dependent manner. These findings demonstrate the improved stability and applicability of the produced biocatalysts in varying reaction environments.