ULTRASOUND, BIOPOLYMERS AND TEMPERATURE: EFFECT ON THE O/W EMULSIONS STABILITY

The mixture of two or more biopolymers when applied to stabilize emulsions can provide phase separation due to instability and thermodynamic incompatibility. In some cases, the phase rich in biopolymers presents the emulsified oil phase generating the cream, which can exhibit droplet size and interesting rheological properties similar to those of an emulsion. The objective of this work was to evaluate the droplet size distribution (DSD), the chemical composition of the phases and the temperature effect on the viscosity of oil-water emulsions stabilized by electrostatic interaction between soy protein isolate (SPI) and high methoxyl pectin (PEC) at pH 3.5 in SPI:PEC proportions (1:1; 4:1) and oil contents (5-15%) subjected to sonication. Emulsions were prepared by dispersing soybean oil in the SPI solution using Ultra-Turrax at 15000 rpm for 4 minutes, followed by the addition of PEC and agitation for 4 minutes. Subsequently, they were sonicated for 1 minute at 20 kHz/120W and kept at rest for 48 hours. DSD was determined by laser diffraction. The chemical composition of the unstable emulsions was investigated for the serum and cream phases. Heating-cooling ramps of 1:1 and 4:1 emulsions with 15 % oil were obtained in the following order: 25-72ºC; 72-5ºC and 5-25ºC at 2ºC/min. The 1:1 emulsions and the 4:1 creams showed bimodal distribution with mean diameter D3,2 = 3.36-4.4 μm and D3,2 = 13-15.5 μm, respectively. The increase in oil content led to a proportional increase in diameter. The creaming index of the 4:1 emulsions showed values of 46.2-38.6%. Considering that the oil in the system tends to lodge in the cream phase, the increase in the volume occupied by the cream phase can be attributed to the increase in the mass (or volume) of oil present in the emulsion. This was confirmed by the chemical composition, since in the cream phase the variables with a significant effect (p ≤ 0.05) were oil and water content. In the cream phase, there was a greater amount of protein and lipids and a smaller amount of water and carbohydrates, proving that the SPI was adsorbed at the oil-water interface, creating a protective membrane. On the other hand, the insufficient amount of pectin favored the destabilization. The heating-cooling ramps at 25°C showed similar viscosity values, indicating that the emulsions were restored, a reversible gel behavior characteristic of pectin. The cream viscosity was higher due to greater packing of the drops, partially eliminating the aqueous phase, in addition to the ability of SPI to form irreversible gels at 65°C. Emulsions and creams showed small droplets, rheological characteristics showed the effect of temperature and the biopolymer present in the systems composition. Such factors intensified the cream viscosity, which becomes interesting, since the acceptance of various semi-solid and liquid foods depends on the viscosity or consistency of the product. Additionally, soy proteins are an option to milk proteins for people who are lactose intolerant or who are allergic to milk.