Abstract
Aqueous dispersions of tripalmitin particles (with a minimum size of 130 nm) were produced, via a hot sonication method, with and without the addition of food-grade emulsifiers. Depending on their relative size and chemistry, the emulsifiers altered the properties of the fat particles (e.g. crystal form, dispersion state and surface properties) by two proposed mechanisms. Firstly, emulsifiers modify the rate and/or extent of polymorphic transitions, resulting in the formation of fat crystals with a range of polarities. Secondly, the adsorption of emulsifiers at the particle interface modifies crystal surface properties. Such emulsifier-modified fat particles were then used to stabilise emulsions. As the behaviour of these particles was predisposed by the kind of emulsifier employed for their manufacture, the resulting particles showed different preferences to which of the emulsion phases (oil or water) became the continuous one. The polarity of the fat particles decreased as follows: Whey Protein Isolate > Soy Lecithin > Soy Lecithin + Tween 20 > Tween 20 > Polyglycerol Polyricinoleate > no emulsifier. Consequently, particles stabilised with WPI formed oil-in-water emulsions (O/W); particles stabilised solely with lecithin produced a highly unstable W/O emulsion; and particles stabilised with a mixture of lecithin and Tween 20 gave a stable W/O emulsion with drop size up to 30 μm. Coalescence stable, oil-continuous emulsions (W/O) with drop sizes between 5 and 15 μm were produced when the tripalmitin particles were stabilised with solely with Tween 20, solely with polyglycerol polyricinoleate, or with no emulsifier at all. It is proposed that the stability of the latter three emulsions was additionally enhanced by sintering of fat particles at the oil-water interface, providing a mechanical barrier against coalescence.
Highlights
Stabilising interfaces with particles (i.e. Pickering stabilisation) is an established approach,[1,2,3,4,5] which aims at extending the kinetic stability of simple and multiple emulsions
We propose that lecithin molecules either promote zone refinement of the fat matrix by aiding the polymorphic transitions or, due to a similarity in the molecular structure, facilitate fat crystallisation in the most stable crystal form (Fig. 4)
We have shown that by using a variety of food grade emulsifiers, tripalmitin particles with different characteristics with respect to their emulsion-forming tendencies can be produced
Summary
Stabilising interfaces with particles (i.e. Pickering stabilisation) is an established approach,[1,2,3,4,5] which aims at extending the kinetic stability of simple and multiple emulsions This is because interfaces covered with colloidal particles provide an enhanced barrier to droplet coalescence,[6] mass transfer across the interface[5] and lipid oxidation.[4] A range of food-grade particles have been investigated for use in Pickering stabilisation. These include wax crystals,[7] CaCO3,8 ethyl cellulose,[9] proteinpolysaccharide complexes,[10] fat crystals,[5] OSA modified starch[11] etc. Amongst the several factors (i.e. particle wettability, size, shape, concentration, particle–particle interactions) determining whether the solid particles will act as an emulsifier, the most important is often argued to be wettability, which is measured by the contact angle that the particles assume at the 2712 | Food Funct., 2016, 7, 2712–2721
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