Spontaneous emulsification of fish oil at a substantially low surfactant-to-oil ratio: Emulsion characterization and filled hydrogel formation

Abstract

Fish oil was spontaneously emulsified in a low-acyl gellan solution by the surfactant polyoxyethylene sorbitan monooleate (Tween 80) at different ratios of surfactant-to-oil (SOR). A minimum content of 4 mg g−1 of gellan at aqueous phase was necessary to produce stable emulsions at the SOR of 1.0. Higher gellan contents allowed reduction of SOR. A fully stable emulsion for 60 days was prepared at a gellan concentration of 6 mg g−1 and SOR of 0.1. Gellan concentration also influenced the oil droplet size and ζ-potential, as well as, the consistency coefficient of emulsion. As gellan decreased the surface tension at the air/water interface from ≈71.96 mN/m to ≈52.35 mN/m, we hypothesized that gellan co-adsorbed together with Tween onto oil drops surface. The spontaneously emulsified fish oil did not undergo oxidation during storage for 21 days.Emulsion samples were supplemented with Ca2+ to undergo gelation. Fourier-transform infra-red (FT-IR) spectroscopy indicated that hydrogen bonding and ionic interactions contributed to filled hydrogels (emulsion gels) formation. The lower the gellan content, the softer was the texture and more porous was the microstructure of filled hydrogels. A lower gellan content also resulted in higher swelling degree of freeze-dried filled hydrogels upon immersion in an aqueous solution. It was concluded that oil droplets by adsorbing gellan onto their surface played a prominent role in filled hydrogels swellability. The resulting filled hydrogels were less crystalline compared to the gellan powder and crystallinity corresponded to gel microstructure.