Supramolecular assembly strategy of modified starch chains for achieving recyclable emulsion biocatalysis within a narrow pH range.

Stimuli-responsive Pickering emulsions are promising in biocatalysis for their ease of product separation and emulsifier recovery. However, pH responsiveness, though simple and cost-effective, faces challenges in precise control and narrow transition ranges, limiting its use in enzymatic catalysis. Herein we introduced amorphous octenyl succinic anhydride-modified debranched starch chains (Am-OSA-St) to control emulsion properties within a pH range suitable for enzymatic catalysis. By adjusting the OSA group density and molecular weight, Am-OSA-St allowed emulsions to transition reversibly between pH 7.3 and 5.5 and enabled self-recycling through supramolecular self-assembly. Employing molecular dynamics simulations and physicochemical characterization, we elucidated the control mechanism of oil-water interfaces via the microstructure transformation of Am-OSA-St. The findings revealed that protonation of carboxylate groups disrupted the charge balance and polarity of starch chains, leading to strong electrostatic and van der Waals interactions that drove self-assembly. This entanglement caused starch chains in the aqueous phase to "drag" those at the oil-water interface, moving them into the aqueous phase and forming micelles. These micelles, with a hydrophobic interior and hydrophilic exterior, prevented re-adsorption. Testing with Candida antarctica Lipase B (CALB) and N-acetylneuraminic lyase showed that the pH-regulated emulsion system maintained excellent efficiency and cycling stability in mild conditions.