Synthesis of lipase-hydrogel microspheres and their application in deacidification of high-acid rice bran oil

Abstract

The main challenge of rice bran oil (RBO) as a highly nutritional edible oil is the high content of free fatty acids. Biocatalytic esterification is an effective strategy to reduce acid value of RBO. In this study, polydopamine/hydroxyethyl methacrylate/acrylamide hydrogel microspheres (PHAMs) are designed and synthesized to immobilize lipase. The PHAMs have excellent water retention and provide an oil–water interface for the biocatalytic esterification of lipase. The catalytically active center of lipase is induced to open by the oil–water interface and its catalytic activity is fully developed. At the same time, the micro-water environment provided by hydrogel microspheres prevents hydrolysis of lipid products. Lipase-polydopamine/hydroxyethyl methacrylate/acrylamide hydrogel microspheres (L-PHAMs) exhibit strong immobilization capacity (enzymatic loading is 13.34 mg g⁻¹), enhanced activity (1.11-fold that of free lipase), and excellent reusability (it maintained 37.8% of the free lipase activity after 10 cycles). The L-PHAMs still maintain 86.24% of the initial enzymatic activity after 15 days, while the free lipase activity is only 25.31%. In addition, kinetic determination shows an increased affinity between L-PHAMs and the substrate (K_m is 1.07 μmol L⁻¹). High-acid rice bran oil (HBRO) is successfully deacidified by an esterification reaction using L-PHAMs as catalysts. This process enabled an unprecedented deacidification efficiency of up to 98.19% in a short time (2 h). Overall, biocatalytic esterification by L-PHAMs is an economical and sustainable deacidification method.