Magnetic Switchable Pickering Interfacial Biocatalysis: One-Pot Cascade Synthesis of Phytosterol Esters from High-Acid Value Oil

The traditional reutilization of high-acid value oil resources causes pollution, suffers from high energy consumption, and brings relatively low economic value. In this study, high-acid value oil was converted into high-value product phytosterol esters (PEs) using a "one-pot" enzymatic cascade reaction strategy including the hydrolysis of high-acid value oils into free fatty acids (FFAs) and followed by its esterification of phytosterols. Lipase AYS was immobilized on magnetic hollow mesoporous carbon nanospheres to obtain AYS@MHMCS, forming a sustainable and solvent-free Pickering interfacial biocatalysis platform. Each droplet in the emulsion system served as a microreactor with the reactants in the oil phase; the byproduct glycerol was spontaneously excreted to the aqueous phase which would "push" the hydrolysis reaction forward. The products of hydrolysis (fatty acids) remained in the oil phase, continuing the next esterification reaction with phytosterols, which ensured the efficient and continuous operation of the tandem reaction. Benefiting from the interfacial activation effect of lipase, the catalytic efficiency of the emulsion system was 30 times that of the single-phase system. The yield of PEs was up to 90%, while the highest in the single-phase was only 30%. Additionally, the magnetic-responsive Pickering emulsion could recover AYS@MHMCS intactly in 15 min, and there would be no significant loss of catalytic activity even after continuous reuse for 15 cycles. This method not only provides a robust biocatalysis technique with a sustainable interface but also paves the way to high-value utilization of high-acid value oil resources.