Plant-Based Oil-in-Water Food Emulsions: Exploring the Influence of Different Formulations on Their Physicochemical Properties
Carolina Quezada, Matías Urra, Camila Mella, Rommy N. Zúñiga, Elizabeth Troncoso
Abstract
The global focus on incorporating natural ingredients into the diet for health improvement encompasses ω-3 polyunsaturated fatty acids (PUFAs) derived from plant sources, such as flaxseed oil. ω-3 PUFAs are susceptible to oxidation, but oil-in-water (O/W) emulsions can serve to protect PUFAs from this phenomenon. This study aimed to create O/W emulsions using flaxseed oil and either soy lecithin or Quillaja saponins, thickened with modified starch, while assessing their physical properties (oil droplet size, ζ-potential, and rheology) and physical stability. Emulsions with different oil concentrations (25% and 30% w/w) and oil-to-surfactant ratio (5:1 and 10:1) were fabricated using high-pressure homogenization (800 bar, five cycles). Moreover, emulsions were thickened with modified starch and their rheological properties were measured. The physical stability of all emulsions was assessed over a 7-day storage period using the TSI (Turbiscan Stability Index). Saponin-stabilized emulsions exhibited smaller droplet diameters (0.11–0.19 µm) compared to lecithin (0.40–1.30 µm), and an increase in surfactant concentration led to a reduction in droplet diameter. Both surfactants generated droplets with a high negative charge (−63 to −72 mV), but lecithin-stabilized emulsions showed greater negative charge, resulting in more intense electrostatic repulsion. Saponin-stabilized emulsions showed higher apparent viscosity (3.9–11.6 mPa·s) when compared to lecithin-stabilized ones (1.19–4.36 mPa·s). The addition of starch significantly increased the apparent viscosity of saponin-stabilized emulsions, rising from 11.6 mPa s to 2117 mPa s. Emulsions stabilized by saponin exhibited higher stability than those stabilized by lecithin. This study confirms that plant-based ingredients, particularly saponins and lecithin, effectively produce stable O/W emulsions with flaxseed oil, offering opportunities for creating natural ingredient-based food emulsions.