Effects of pectin and guar gum on creaming stability, microstructure and rheology of egg yolk plasma-stabilized emulsions

The influence of pectin and guar gum on the creaming stability, microstructure and rheological properties of 1.0% (w/v) egg yolk plasma (EYP)-stabilized 25.0% (v/v) soybean oil-in-water emulsions was studied at pH 7.0. Addition of pectin/guar gum decreased creaming percentage, and no creaming was detected in the presence of 0.5% (w/v) pectin/guar gum as a result of increasing viscosity. At the end of 10 h, creaming percentage decreased from 61 to 57% with the addition of 0.05% (w/v) guar gum and to 39% with the addition of 0.2% (w/v) guar gum. Microscopic observations represented the droplet aggregation arising from the presence of nonabsorbing biopolymers. At (gamma) over dot = 10 s(-1), a tenfold increase in viscosity was observed in the presence of 0.5% (w/v) guar gum compared to the presence of 0.1% guar gum due to the thickening effect of polysaccharide. Increasing gum concentrations enhanced the viscosity and hence the consistency index. All emulsions, except for those containing 0.5% (w/v) guar gum, reflect the near-Newtonian behaviour with flow behaviour index, n, of 0.9-1.0. All emulsions exhibited a liquid-like behaviour at low frequencies (<7.0 Hz) where G '' values were higher than G'. Both G' and G '' showed a frequency dependency and these two moduli crossed each other at higher frequencies (>7.0 Hz), G' became greater than G '' and the system behaved like an elastic solid. Addition of pectin at all levels cause no significant change in G' and G '' values, whereas addition of guar gum, especially at a concentration of 0.5% (w/v), significantly improved these values.