pH and CO2/N2 dual responsive Pickering emulsion stabilized by shellac nanoparticle-enzyme conjugates for synthesis of phytosterol esters.

The development of green and efficient catalytic systems is crucial for sustainable chemical processes. This study engineered shellac nanoparticle-lipase conjugates for biphasic biocatalysis. Taking advantage of the inherent amphiphilicity and pH-triggered interfacial behavior of the shellac, the conjugates exhibited dual functionality as intelligent Pickering emulsifiers and interfacial biocatalysts. The covalent conjugation strategy achieved a protein loading capacity of 107.97 ± 5.24 mg/g under optimized conditions while preserving interfacial responsiveness. Reversible emulsification/breaking transitions were precisely regulated at least 30 times through pH adjustment or alternating CO₂/N₂ treatments, enabling convenient catalyst recovery. When applied to the esterification of phytosterols with oleic acid, the conjugates exhibited a higher esterification rate (78.93 %, 1.5-fold enhancement compared with the free lipase), retained 85.0 % initial catalytic activity after six consecutive cycles. The responsive Pickering system combined exceptional recyclability and enhanced catalytic performance, providing an innovative pathway for the development of Pickering interfacial catalysis.