Abstract
Oleofoams are dispersions of gas bubbles in a continuous oil phase and can be stabilized by crystals of fatty acids or waxes adsorbing at the oil-air interface. Because excess crystals in the continuous phase form an oleogel, an effect of the bulk rheology of the continuous phase is also expected. Here, we evaluate the contributions of bulk and interfacial rheology below and above the melting point of a wax forming an oleogel in sunflower oil. We study the dissolution behaviour of single bubbles using microscopy on a temperature-controlled stage. We compare the behaviour of a bubble embedded in an oleofoam, which owes its stability to both bulk and interfacial rheology, to that of a bubble extracted from the oleofoam and resuspended in oil, for which the interfacial dilatational rheology alone provides stability. We find that below the melting point of the wax, bubbles in the oleofoam are stable whereas bubbles that are only coated with wax crystals dissolve. Both systems dissolve when heated above the melting point of the wax. These findings are rationalized through independent bulk rheological measurements of the oleogel at different temperatures, as well as measurements of the dilatational rheological properties of a wax-coated oil-air interface.
Highlights
Foaming of edible oils to form oleofoams is used in the design of food products with reduced fat content (Binks and Marinopoulos 2017; Heymans et al 2017)
Our study of the dissolution of bubbles in an oleofoam, in conjunction with bulk and interfacial rheological measurements, has shown that crystals adsorb to the interfaces of bubbles, the Pickering mechanism of stabilisation is insufficient to arrest bubble dissolution
We found that for bubbles isolated from the oleogel matrix but possessing an interfacial wax layer, even though the Gibbs criterion for bubble stability is met, dissolution is not arrested: peeling of the wax layer from the air-oil interface is energetically more favourable than elastic compression of the layer
Summary
Foaming of edible oils to form oleofoams is used in the design of food products with reduced fat content (Binks and Marinopoulos 2017; Heymans et al 2017). Crystals can adsorb at the air-oil interfaces of the bubbles (Mishima et al 2016; Heymans et al 2017) and impart interfacial elasticity, similar to that observed for aqueous Pickering foams (Basheva et al 2011; Beltramo et al 2017; Binks 2002; Hunter et al 2008; Stocco et al 2011), preventing bubble dissolution Another contributing factor is the rheology of the bulk oleogel formed by the crystals remaining in the oil phase.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
