Optimization of emulsion stability with protein-polysaccharide complexes: Effects of soy protein/sodium alginate ratio and of homogenization methods

Mixtures of soy protein isolate and sodium alginate that result in phase separation under certain conditions are of interest for creating new structures and acting as emulsifiers/stabilizers of emulsions, and the performance of the formed supramolecular structures can be affected by the homogenization method applied. The aim of this study was to evaluate the interaction between soy protein isolate (SPI) and sodium alginate (ALG) at varying SPI:ALG ratios (1:1–5:1), with and without ultrasound (US) treatment, and to characterize their physical properties. Additionally, we assessed the stability of emulsions with different oil contents (15 %, 20 % and 25 %) formulated using SPI:ALG ratios of 1:1 and 4:1. Emulsions were prepared using two homogenization methods: ultrasound and high-pressure processing. Biopolymers showed the highest interaction at pH 3.5. Turbidimetry indicated greater complexation at higher protein ratios, and sonication reduced the complex sizes. All sonicated emulsions were unstable, presenting cream phases with large droplet sizes, shear-thinning behavior, and G’ > G’’, characterizing structured materials. However, emulsions with a higher alginate concentration (1:1) presented longer stability. High-pressure homogenized emulsions were completely stable, with D 3,2 around 38 μm. Heating-cooling ramps demonstrated the effect of temperature and the biopolymer’s ratio. Confocal microscopy indicated that emulsion destabilization occurred through flocculation and coalescence. Ultrasound provided creams with better attributes and stability for 7 days, while high pressure stabilized the emulsions, allowing for various applications in the food industry. • Strong SPI-alginate complexation at pH 3.5 in all ratios, shear-thinning and G’>G’’. • Ultrasound reduced values of G’ and G’’ in comparison to samples without sonication. • 1:1 US emulsions tended to be stable, with a turbid aqueous phase. • 1:1 HP treated emulsions were stable, monomodal distribution and small droplets. • Heating ramps showed the influence of the predominant biopolymer in the systems.