Comparative studies of free and immobilized partially purified lipase from Aspergillus niger NRRL-599 produced from solid-state fermentation using gelatin-coated titanium nanoparticles and its application in textile industry

Background and objective Lipases (triacylglycerol acylhydrolase, EC. 3.1.1.3) belong to a class of hydrolases that are specific for the hydrolysis of fats into fatty acids and glycerol that have much application in different industrial processes. Fungi, yeast, and bacteria have been reported to be sources of lipase. There are many immobilized methods for enzyme, and the commonly used methods are physical adsorption, entrapment, and cross-linkage. This study aimed to evaluate lipase production by Aspergillus niger NRRL-599 in solid cultivation using agro-industrial waste as a substrate. Partial purification of the crude enzyme and its characterization and immobilization using nanoparticles were carried out. The potential application of the immobilized and partially purified enzyme was also studied in the field of textile. Materials and methods Partially purified A. niger NRRL-599 lipase was immobilized by physical adsorption onto modified titanium dioxide nanoparticles using gelatin and palmitic acid binders and characterized by transmission electron microscopy, dynamic light scattering, and Fourier-transform infrared. Results and conclusion In our study, lipase produced by A. niger NRRL-599 was partially purified by ammonium sulfate at 60% saturation and immobilized on gelatin-coated titanium dioxide. Comparison between the properties of the free and the immobilized A. niger NRRL-599 lipase forms was carried out. The optimum pH was 9.0 and 10.0 for the free and immobilized forms, respectively. The half-life of the soluble-free lipase at 50 and 55°C was 17.3 and 23.1 min, respectively, whereas for the immobilized form was 23.1 and 34.6 min, respectively. At 50 and 55°C, the deactivation rate constants (kD) for soluble lipase were 6.6×10−3 and 5×10−3, respectively, and 6.6×10−3 and 3.3×10−3, respectively, for immobilized lipase. The Km was 11.11 and 12.5 mM for the immobilized and free forms, respectively. The Vmax was 416.6 U/mg protein and 296.3 U/mg protein for immobilized and free lipase forms, respectively. This confirms that the apparent affinity toward the substrate increases by immobilization. Partially purified lipase and immobilized enzymes were used in the textiles in the treatment of wool fibers before dying to improve the color strength.