Creaming stability of oil in water (O/W) emulsions: Influence of pH on soybean protein–lecithin interaction

In the present work, the influence of pH on stability of oil in water O/W (25:75 w/w) emulsions prepared with soy isolates and lecithin (Lec) was studied. Emulsions were prepared using native (NSI) and denatured (DSI) soybean isolates, Lec and sunflower oil, with a protein–Lec ratio of 10:1. Dispersions of soybean proteins were adjusted to pH 2.0–6.2. Emulsions were optically characterized by droplet size distribution and using a vertical scan analyzer (Quick Scan) to determine the creaming destabilization and the corresponding kinetics involved. At pH 2, a negative effect was observed on droplet size distribution and stability of Lec emulsion. Changes in droplet size and creaming rate as a function of pH value were observed for NSI–Lec and DSI–Lec emulsions in comparison with their corresponding control systems (Lec, NSI, DSI). NSI–Lec emulsions at pH 2.0 presented an important initial emulsifying activity, but the creaming rate recorded was faster than that corresponding to pH 5.5–6.2. For DSI–Lec systems, the stability increased at pH 2.0 and 6.2, values away from the isoelectric point. The presence of Lec enhanced both the initial characteristics reflected in BS0 and droplet size, and the stability against the creaming process.