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Sodium caseinate as a particulate emulsifier for making indefinitely recycled pH-responsive emulsions

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Abstract

pH-responsive emulsions are one of the simplest and most readily implementable stimuli-responsive systems. However, their practical uses have been greatly hindered by cyclability. Here, we report a robust pH-responsive emulsion prepared by utilizing pure sodium caseinate (NaCas) as the sole emulsifier. We demonstrate that the emulsification/demulsification of the obtained NaCas-stabilized emulsion can be triggered by simply changing the pH value over 100 cycles, which has never been observed in any protein-stabilized emulsion system. The NaCas-stabilized emulsion maintains its pH-responsive properties even in a saturated salt solution (NaCl ∼ 6.1 M) or seawater. We illustrate how NaCas functions in pH-responsive emulsions and show that when conventional nanoparticles such as zein protein or bare SiO2 particles were coated with a layer of NaCas, the resulting formulated emulsions could be switched on and off over 10 cycles. The unique properties of NaCas thus enable the engineering of conventional Pickering emulsions to pH-responsive Pickering emulsions. Finally, we have integrated catalytically active gold (Au) nanoclusters (NCs) into the NaCas protein and then utilized them to produce emulsions. Remarkably, these NaCas–Au NCs assembled at the oil–water interface exhibited excellent catalytic activity and cyclability, not only in aqueous solution, but also in complicated seawater environments.

Graphical abstract: Sodium caseinate as a particulate emulsifier for making indefinitely recycled pH-responsive emulsions

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Supplementary files

Article information


Submitted
07 Oct 2019
Accepted
16 Mar 2020
First published
16 Mar 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020, Advance Article
Article type
Edge Article

Sodium caseinate as a particulate emulsifier for making indefinitely recycled pH-responsive emulsions

Y. Xi, B. Liu, H. Jiang, S. Yin, T. Ngai and X. Yang, Chem. Sci., 2020, Advance Article , DOI: 10.1039/C9SC05050G

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