Tiny, yet impactful: Detection and oxidative stability of very small oil droplets in surfactant-stabilized emulsions

Sten Ten Klooster; Machi Takeuchi; Karin Schroën; Remco Tuinier; Rick Joosten; Heiner Friedrich; Claire Berton-Carabin

doi:10.1016/j.jcis.2023.09.005

Tiny, yet impactful: Detection and oxidative stability of very small oil droplets in surfactant-stabilized emulsions

J Colloid Interface Sci. 2023 Dec 15;652(Pt B):1994-2004. doi: 10.1016/j.jcis.2023.09.005. Epub 2023 Sep 4.

Authors

Sten Ten Klooster¹, Machi Takeuchi², Karin Schroën³, Remco Tuinier⁴, Rick Joosten⁵, Heiner Friedrich⁶, Claire Berton-Carabin⁷

Affiliations

¹ Laboratory of Food Process engineering, Wageningen University, P.O. Box 17, Bornse Weilanden 9, 6708 WG Wageningen, the Netherlands. Electronic address: Sten.tenklooster@wur.nl.
² Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands; Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, the Netherlands. Electronic address: m.takeuchi@tue.nl.
³ Laboratory of Food Process engineering, Wageningen University, P.O. Box 17, Bornse Weilanden 9, 6708 WG Wageningen, the Netherlands. Electronic address: Karin.schroen@wur.nl.
⁴ Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands; Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, the Netherlands. Electronic address: r.tuinier@tue.nl.
⁵ Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands; Center for Multiscale Electron Microscopy, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, the Netherlands. Electronic address: r.r.m.joosten@tue.nl.
⁶ Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, the Netherlands; Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, the Netherlands; Center for Multiscale Electron Microscopy, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, the Netherlands. Electronic address: H.Friedrich@tue.nl.
⁷ Laboratory of Food Process engineering, Wageningen University, P.O. Box 17, Bornse Weilanden 9, 6708 WG Wageningen, the Netherlands; INRAE, BIA, 44000 Nantes, France. Electronic address: claire.berton-carabin@inrae.fr.

PMID: 37690307
DOI: 10.1016/j.jcis.2023.09.005

Abstract

Hypothesis: The shelf life of multiphase systems, e.g. oil-in-water (O/W) emulsions, is severely limited by physical and/or chemical instabilities, which degrade their texture, macroscopic appearance, sensory and (for edible systems) nutritional quality. One prominent chemical instability is lipid oxidation, which is notoriously complex. The complexity arises from the involvement of many physical structures present at several scales (1-10,000 nm), of which the smallest ones are often overlooked during characterization.

Experiments: We used cryogenic transmission electron microscopy (cryo-TEM) to characterize the coexisting colloidal structures at the nanoscale (10-200 nm) in rapeseed oil-based model emulsions stabilized by different concentrations of a nonionic surfactant. We assessed whether the oxidative and physical instabilities of the smallest colloidal structures in such emulsions may be different from those of larger colloidal structures.

Findings: By deploying cryo-TEM, we analyzed the size of very small oil droplets and of surfactant micelles, which are typically overlooked by dynamic light scattering when larger structures are concomitantly present. Their size and oil content were shown to be stable over incubation, but lipid oxidation products were overrepresented in these very small droplets. These insights highlight the importance of the fraction of "tiny droplets" for the oxidative stability of O/W emulsions.

Keywords: Cryo-transmission electron microscopy (TEM); Droplets; Dynamic light scattering; Emulsion; Lipid oxidation; Microemulsion; Nanoemulsion; Surfactants; Swollen micelles; Winsor system.