Modulation of pH Sensitivity of Surface Charge and Aggregation Stability of Protein-Coated Lipid Droplets by Chitosan Addition

Abstract

The impact of a cationic polyelectrolyte on the pH sensitivity of the electrical charge and aggregation stability of protein-coated lipid droplets was examined. One percent (w/w) corn oil-in-water emulsions containing lipid droplets coated by β-lactoglobulin [0.05% (w/w) β-Lg, 10 mM acetate buffer, pH 3] were prepared in the absence ("primary" emulsions) and presence ("secondary" emulsions) of chitosan (0 to 0.05 wt%). The pH (3 to 8) of these emulsions was adjusted, and the particle charge, particle size, creaming stability, and microstructure were measured. Chitosan adsorbed to the β-Lg-coated droplets from pH 4.5 to 7.5, which was attributed to electrostatic attraction between the cationic polyelectrolyte and anionic patches on the droplet surfaces. Droplets coated by β-Lg-chitosan had better stability to flocculation than those coated by β-Lg alone around the isoelectric point of the adsorbed proteins (pH 4.5 to 5.5), which was attributed to increased electrostatic and steric repulsion between the droplets. We have shown that chitosan may be used to modulate the electrical characteristics and stability of protein-coated lipid droplets, which may be useful in the design and formation of delivery systems for use in the food, pharmaceutical, and other industries.

Multilayer Oil-in-Water Emulsions: Formation, Characteristics and Application as the Carriers for Lipophilic Bioactive Food Components – a Review

“…SDS is a non-food-grade emulsifier, but it does represent a number of small-molecule anionic surfactants that are commonly used in foods, can be obtained in high purity and its properties are generally well understood [Stauffer, 2001;Surh et al, 2005;Thanasukarn et al, 2006]. It has been found that surfactant-coated droplets remain highly negative across a wide pH range [Hong & McClements, 2007]. This severely limits the application of food-grade polysaccharides that can be used to produce multilayered membranes, since most of them are also anionic .…”

“…In an acid environment chitosan behaves as polycationic electrolyte and this yields antifungal or antimicrobial activities since cations can bind to anionic sites on bacterial and fungal cell wall surfaces [de Vos et al, 2010;Weiss et al, 2006]. However, at higher pH, it tends to lose its charge and may precipitate from solution due to deprotonation of the amino groups [Hong & McClements, 2007]. It should be also underlined that the pK a of the ionizable groups on a polyelectrolyte can be shifted from their values in solution due to their local electrostatic environment.…”

“…The pH of the solution is then adjusted to change the electrical charge on either the droplets and/or the polyelectrolyte molecules so that the polyelectrolyte adsorbs to the droplets surfaces through electrostatic attraction (e.g. a pH where the droplet and polyelectrolyte have opposite charges) [Hong & McClements, 2007;Hu et al, 2011;McClements, 2012]. A washing step may be required between each electrostatic deposition step in order to remove any excess of non-adsorbed biopolymer remaining FIGURE 1.…”

Modification of interfacial characteristics of monodisperse droplets produced using membrane emulsification by surfactant displacement and/or polyelectrolyte electrostatic deposition

“…β-lactoglobulin (β-Lg) is often used as an emulsifier to stabilize O/W emulsions because it is a natural polymer with good biocompatibility [19][20][21][22][23]. For emulsions initially coated with Tween 20, the charge on the droplets went from −12 to +20 mV when the β-lactoglobulin concentration in the continuous phase was increased from 0 to 0.2 wt% (Fig.…”

“…CP: 0.05% β β β β-Lg, pH 3 (ξ 1 = +60 mV) DP: 1% corn oil. CP: 0.05% β β β β-Lg, 0.01% chitosan, pH 3 → 6 (ξ 1 → −16 mV, ξ 2 → +11 mV) [23] DP: 15% tuna oil. CP: 3% lecithin, pH 3 (ξ 1 = −52 mV) DP: 5% tuna oil.…”