pH-Switchable Pickering Interfacial Biocatalysis: One-Pot Enzymatic Synthesis of Phytosterol Esters with Low-Value Rice Bran Oil

Herein, a pH-switchable Pickering interfacial biocatalysis (PIB) system is proposed and applied to a solvent-free biphasic biocatalysis. The oil-in-water emulsion was stabilized by amine-functionalized hollow mesoporous silica nanospheres (HMSS-N), which is functioned as emulsifiers of PIB and carriers of lipase AYS. The smart emulsifiers exhibited switch of the surface wettability behaviors in response to abrupt changes of pH. Under the optimality conditions, the immobilized lipase loading amount, activity, and expressed activity were 174.1 mg g–1, 9073 U g–1, and 52.1 U g–1 protein, respectively, at pH 6. Based on it, the hydrolysis of rice bran oil and esterification with phytosterols to produce phytosterol esters (PEs) were successfully performed. Compared with the conventional free enzyme one-phase system, the PIB system displays a higher reaction efficiency (catalytic efficiency value 6.88 mmol g–1 h–1, 20-fold enhancement). In addition, the system maintains 95% residual activity after 10 reaction cycles with 38.3 g products/g biocatalyst average productivity, complying with the requirements of industry-accepted standards. In each cycle, the demulsification is realized simply by in situ pH regulation. Therefore, this paper provides a powerful and green platform for oil–fat modification and stimuli-responsive interfacial biocatalysis with the advantages of a high efficiency, sustainability, a solvent-free process, and multi-recyclability.