BslA-stabilised emulsion droplets with designed microstructure

TL;DR

This paper demonstrates that BslA protein can stabilize non-spherical emulsion droplets with controlled microstructures, enabling tailored emulsion properties for various applications.

Contribution

It introduces the use of BslA to stabilize anisotropic droplets and control their morphology and stability through freezing and melting processes.

Findings

BslA stabilizes anisotropic emulsion droplets.

Frozen BslA-stabilized droplets can be manipulated to induce coalescence.

Droplet structure is retained after melting when sufficient BslA is present.

Abstract

Emulsions are a central component of many modern formulations in food, pharmaceuticals, agrichemicals and personal care products. The droplets in these formulations are limited to being spherical as a consequence of the interfacial tension between the dispersed phase and continuous phase. The ability to control emulsion droplet morphology and stabilise non-spherical droplets would enable the modification of emulsion properties such as stability, substrate binding, delivery rate and rheology. One way of controlling droplet microstructure is to apply an elastic film around the droplet to prevent it from relaxing into a sphere. We have previously shown that BslA, an interfacial protein produced by the bacterial genus Bacillus, forms an elastic film when exposed to an oil- or air-water interface. Here, we highlight BslA's ability to stabilise anisotropic emulsion droplets. First, we show that BslA is capable of arresting dynamic emulsification processes leading to emulsions with variable morphologies depending on the conditions and emulsification technique applied. We then show that frozen emulsion droplets can be manipulated to induce partial coalescence. The structure of the partially coalesced droplets is retained after melting, but only when there is sufficient free BslA in the continuous phase. That the fidelity of replication can be tuned by adjusting the amount of free BslA in solution suggests that freezing BslA-stabilised droplets disrupts the BslA film. Finally, we utilise BslA's ability to preserve emulsion droplet structural integrity throughout the melting process to design emulsion droplets with a chosen shape and size.