Characterisation of a “green” lipase from Aspergillus niger immobilised on polyethersulfone membranes

Resumo

In this work, a “green†Aspergillus niger lipase obtained from the solid-state fermentation of Hancornia speciosa (“mangabaâ€) seeds was efficiently immobilised on polyethersulfone membranes (PES) by physical adsorption (PES-ADS-lipase) and covalent bonding (PES-COV-lipase) (immobilisation yields of 92 and 81%, respectively). The free lipase showed an optimum pH close to neutrality, while the biocatalysts displaced the pH to the alkaline region (optimum pH 9.0 and 11.0 for PES-ADS-lipase and PES-COV-lipase, respectively). The optimum temperature of free lipase was 55°C; however, a higher thermal stability occurred at 37°C. The PES-ADS-lipase and PES-COV-lipase showed lower optimum temperatures (37 and 45°C, respectively) but higher thermal stabilities at 45 and 55°C, respectively. The lower thermal inactivation constant and higher half-life of PES-COV-lipase at 55°C confirmed the efficiency of covalent bonding in maintaining the thermal stability of the enzyme. The Michaelis - Menten constant (K_m) and maximum rate of reaction (V_max) were also determined, and the biocatalysts showed higher affinities to substrates (lower K_m values) than free lipase. In this work, the biocatalysts showed good catalytic properties with future potential applications in hydrolysis reactions. The use of a “green†lipase obtained from agroindustrial residue makes this product economically attractive from an industrial point of view.