Emulsions stabilised by whey protein microgel particles: towards food-grade Pickering emulsions

Abstract

We have investigated a new class of food-grade particles, whey protein microgels, as stabilisers of triglyceride-water emulsions. The sub-micron particles stabilized oil-in-water emulsions at all pH with and without salt. All emulsions creamed but exhibited exceptional resistance to coalescence. Clear correlations exist between the properties of the microgels in aqueous dispersion and the resulting emulsion characteristics. For conditions in which the particles were uncharged, fluid emulsions with relatively large drops were stabilised, whereas emulsions stabilized by charged particles contained smaller flocculated drops. A combination of optical microscopy of the drops and spectrophotometry of the resolved aqueous phase allowed us to estimate the interfacial adsorption densities of the particles using the phenomenon of limited coalescence. We deduce two classes of particle arrangement. Complete adsorption of the particles was obtained when they were neutral or when their charges were screened by salt resulting in at least one particle monolayer at the interface. By contrast, only around 50% of the particles adsorbed when they were charged with emulsion drops being covered by less than half a monolayer. These findings were supported by direct visualization of drop interfaces using cryo-scanning electron microscopy. Uncharged particles were highly aggregated and formed a continuous 2-D network at the interface. Otherwise particles organized as individual aggregates separated by particle-free regions. In this case, we suggest that some particles spread at the interface leading to the formation of a continuous protein membrane. Charged particles displayed the ability to bridge opposing interfaces of neighbouring drops to form dense particle disks protecting drops against coalescence; this is the main reason for the flocculation and stability of emulsions containing sparsely covered drops.

In vitro digestion of Pickering emulsions stabilized by soft whey protein microgel particles: influence of thermal treatment

“…The Z-average diameter of 311 nm (Table 1) with a low polydispersity index (0.15) was in good agreement with d 32 value and the particle size observed in the micrographs. The Z-average diameter and -potential of the WPM particles at pH 7.0 was in good agreement with a previous study 28 , where these soft particles were obtained by a different processing route.…”

“…Although a great many studies have been conducted on Pickering emulsions using traditional inorganic or synthetic particles, there is a relative paucity of literature on food-compatible particulate materials from natural edible sources, examples, include cellulose nanocrystals 22 , chitin nanocrystals 23 , modified starch 24 , soy protein nanoparticles 25 , flavonoid particles 26 , micellar casein coated nanoemulsion droplets 27 and whey protein microgels 28,29 . Soft solid particles such as whey protein microgels can be a particularly effective system to resist displacement by bile salts because soft solid particles deform during adsorption increasing the adsorption energies by orders of magnitude relative to rigid particles 30 .…”

Two-step sequential cross-linking of sugar beet pectin for transforming zein nanoparticle-based Pickering emulsions to emulgels

“…These systems are conventionally stabilized by means of (chemically-synthesized) M a n u s c r i p t 4 surface active agents to reduce the dispersed phase/continuous phase interfacial tension (Destribats, Rouvet, Gehin-Delval, Schmitt, & Binks, 2014). Over the past decades, surfactantfree emulsions have been studied and developed enthusiastically by food scientists due to the documented adverse effects of some small-molecule surfactants on human health (Frelichowska, Bolzinger, & Chevalier, 2010).…”

“…Starch particles (Marku, Wahlgren, Rayner, Sjöö, & Timgren, 2012;Tan, Xu, Liu, Li, Lu, & Wang, 2012), chitin nanocrystals (Tzoumaki, Moschakis, Kiosseoglou, & Biliaderis, 2011), polymergrafted cellulose nanocrystals (Zoppe, Venditti, & Rojas, 2012), chitosan nanoparticles (Wei, Wang, Zou, Liu, & Tong, 2012) and whey protein microgels (Destribats et al, 2014) are examples of bioparticles employed at Pickering emulsions preparation and stabilization. Being an amphiphilic and generally recognized as safe (GRAS) biomacromolecule, zein is of great potential for fabrication of particle emulsifiers with biocompatible and biodegradable characteristics.…”

Contact-line pinning controls how quickly colloidal particles equilibrate with liquid interfaces

“…Particles can stabilize oil-water interfaces in Pickering emulsions, [1] which are used in food, [2,3] oil recovery, [4] pharmaceuticals, and cosmetics. [5] Oil-water interfaces can also be used to scaffold the assembly of particles into colloidosomes, [6] Janus particles, [7] monolayers, [8] and photolithography masks.…”