Functionalizing soy protein nano-aggregates with pH-shifting and mano-thermo-sonication

Plant protein-mediated nano-delivery systems have gained increasing attention in the food and pharmaceutical industries in recent years. Several physical and chemical methods for improving the functional properties of plant proteins with respect to the native forms have been proposed. This study presents a new approach, which combines pH-shifting and mano-thermo-sonication (MTS) to produce soy protein nano-aggregates with significantly improved functional properties. Soy-protein isolate (SPI) was treated with pH-shifting at pH 12 or in combination with MTS and high-pressure homogenization (HPH). Response Surface Methodology was used to find the optimal conditions (50 °C, 200 kPa, and 60 s) for the MTS. The combination of pH-shifting and MTS resulted in spherical SPI aggregates of the smallest size, 27.1 ± 1 nm, as shown by transmission electron microscopy. The SPI nanoaggregates were used to prepare oil-in-water nanoemulsions with canola oil, which exhibited good stability over 21 days at 4 °C. In addition, the pH 12-MTS samples had resulted in the highest protein solubility, lowest turbidity, free sulfhydryl and disulfide bonds, surface hydrophobicity, antioxidant activity, and rheological and emulsifying properties than the other samples.