Abstract
Adsorption-crosslinking is one of the immobilization methods to improve the reusability of lipase. It requires amino groups to reduce cross-link immobilization risk so that lipase–support interaction increases and the immobilization is attainable. Also, the amino group on the support is expected to increase lipase performance. This study aimed to analyze the effect of amino group addition on immobilized Aspergillus niger lipase by the adsorption-crosslinking using MP-64 macroporous anion resin and XAD-7HP macroporous nonionic resin that has been treated with chitosan. The chitosan-coated resin was characterized by Fourier transform infrared spectrometry (FTIR) and scanning electron microscope (SEM). Lipase immobilization was carried out by adding 10 ml lipase solution containing 0.75 g resins and shaken at 25°C for 150 rpm. Adsorption was achieved for 4 h, followed by cross-linking separately (adding 0.5% (v/v) glutaraldehyde and re-reacting for 20 min). Lipase activity was measured with the titrimetric of olive oil emulsion; mixed with Aspergillus niger lipase, emulsion, and a buffer solution (pH 6.5, ionic strength of 0.7); and incubated for 30 min at 37°C. The effect of amino-functional groups was investigated based on lipase loading and lipase activity. The best lipase loading and lipase activity of 83.79% and 29.41 U/g support were achieved in the adsorption-crosslinking using MP-64 resin coated with chitosan. After four cycles, biodiesel synthesis was maintained at 70.61% of the initial yield. These results indicated that chitosan as an affordable and readily available source of amino groups could be used to modify support for Aspergillus niger lipase immobilization.
Highlights
Interest in substitute for conventional diesel fuel to biodiesel has occurred in several countries due to the massive use of nonrenewable diesel fuel
Since the enzyme form is not explicitly affected by the catalysis properties, we have demonstrated the characteristics of activity analysis, enzyme loading, and biodiesel application
Modification of the support using chitosan-coated resins has been shown to increase the amino-functional groups on the surface
Summary
Interest in substitute for conventional diesel fuel to biodiesel has occurred in several countries due to the massive use of nonrenewable diesel fuel. According to Sheldon and van Pelt (2013), Mohamad et al (2015), and Reis et al (2019), enzymatic processes are preferred because they are more environmentally friendly, cost-effective, and sustainable. The use of lipase is preferred because of its catalyst properties with superiority in selectivity, well specificity, and working under mild conditions (Garcia-Galan et al, 2011; Sheldon and van Pelt, 2013; Barbosa et al, 2015; Reis et al, 2019). The use of free lipases in some industries is certainly less economical, sometimes hampered by environmental instability, such as restriction on its reproducibility (Verma et al, 2013) so that homogenous lipases can be engineered into heterogeneous catalysts with several suitable immobilization techniques in order to recover, separate, and reuse (Cantone et al, 2013). Combining the adsorption and crosslinking methods develops a traditional process capable of increasing enzyme activity and stability during the reaction (Alamsyah et al, 2017)
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