Exploiting Complex Formation between Polysaccharides and Protein Microgels To Influence Particle Stabilization of W/W Emulsions

Abstract

Protein particles were complexed with polysaccharides, and the effect on their capacity to stabilize water-in-water (W/W) emulsions was investigated. Protein microgels were formed by heating aqueous solutions of whey protein isolate. The microgels were subsequently mixed with anionic or cationic polysaccharides: κ-carrageenan (κ-car) or chitosan, respectively. The molar mass and radius of the complexes formed in dilute microgel suspensions (40 mg/L) were characterized by light scattering techniques as a function of the pH and the composition. The structure and stability of complexes formed at a higher microgel concentration (3 g/L) were studied by confocal laser scanning microscopy. It was found that small stable complexes can be formed with κ-car between pH 4.3 and pH 5.5 and with chitosan between pH 4.1 and pH 6.5, that is, both below and above the isoionic point of the microgels (pI = 5.0). Complexation with polysaccharides stabilized aqueous suspensions of microgels in the pH range where they flocculated in the absence of polysaccharides (4.3-5.5). W/W emulsions were produced by mixing dextran and poly(ethylene oxide) solutions. Microgels added to these emulsions spontaneously form a layer around the dispersed droplets, which inhibits coalescence to different extents depending on the conditions. The effect of complexation on the structure of the emulsions was investigated as a function of the pH. It is shown that stable liquid-like emulsions can be obtained in the pH range where emulsions containing only microgels flocculate.

Effect of adding a third polysaccharide on the adsorption of protein microgels at the interface of polysaccharide-based water in water emulsions

“…Whereas the MG clearly adsorbed at the interface (Figure 5B), no accumulation of FITC-PEC at the interface can be seen (Figure 5A), showing that no complexation had occurred between PEC and MG. It was shown elsewhere, using the same methodology, that κ-carrageenan (KC) forms complexes with MG only below pH 5.5 [14]. We found that complexes between MG and PEC also started to be formed only below pH 5.5.…”

“…Attractive interaction between MG can be induced by reducing the pH, but this also leads to large-scale aggregation of MG within the bulk phases [23]. Large-scale aggregation can be avoided by the addition of anionic polysaccharides that bind to the MG at pH < 5.5 [14]. Elsewhere we will show that stable AMP-PUL emulsions can be obtained in this manner at low AMP and PUL concentrations by reducing the pH in the presence of well-chosen small amounts of anionic polysaccharide.…”

“…To these mixtures, protein microgels (MG) were added that were produced by heating whey protein isolate (WPI) solutions at a pH close to the isoelectric point of the protein (pH ~ 5.0). MG have been used in the past to stabilize some types of W/W emulsions [14][15][16][17]. However, in many W/W systems the MG do not adsorb at the interface but partition to one of the phases.…”

Microgels at fluid-fluid interfaces for food and drinks

“…Water-in-water (W/W) emulsions are slightly more exotic, arising mainly where biopolymer solutions phase separate into discrete microscopic regions far richer in one component than the other (Esquena, 2016), (Nicolai and Murray, 2017) (Dickinson, 2019) and all sorts of particles that would prefer not to be in at least one of the aqueous phases can end up concentrated at the W/W interface, preventing further growth of the phase regions via fusion or migration of components between them (Nguyen et al, 2015, Gonzalez-Jordan et al, 2016, Khemissi et al, 2018, Murray and Phisarnchananan, 2016.…”

Electrostatic complexation of β-lactoglobulin aggregates with κ-carrageenan and the resulting emulsifying and foaming properties

“…Like proteins, protein aggregates can complex with polysaccharides. However, few studies have shown the complexation of protein aggregates with polysaccharide and the effects on functional properties (Jones et al, 2011;Khemissi et al, 2018;Wang et al, 2019). The structure of protein aggregates should significantly affect electrostatic complexation of protein-polysaccharide and the functional properties of the complex, which is important in the development of new food ingredients.…”