Combinational effects of acid and salt addition on colloidal, interfacial, and emulsifying properties of purified soybean oil bodies

Abstract

Soybean oil-storing organelles called oil bodies/oleosomes (OBs) are a potential eco-friendly plant-based emulsifier, whereas combinational effects of acid and salt addition on emulsifying properties of OBs were still unclear. This study aimed at investigating colloidal, interfacial, and emulsifying properties of OBs in the presence of acetic acid and NaCl. The purified OBs isolated from soybean seeds were dispersed into 10 mM acetate or phosphate buffer solutions at pH 4.0–7.0 with different NaCl concentrations between 0 and 100 mM. Without added NaCl, the purified OBs were finely dispersed at pH 4.0 and 4.5 by electrostatic repulsion, whereas they aggregated at pH 5.0 and 5.5 probably due to small net charge. The NaCl addition caused screening of the electrostatic interaction between OBs and induced salting-in of OBs. Interfacial tension and interfacial viscoelasticity analyses showed that strongly-charged OBs tended to more slowly sparsely adsorb onto oil-water interface to form less elastic adsorbed layer; this tendency might result from electrostatic adsorption energy barrier between the adsorbed- and non-adsorbed OBs. The OB-stabilized emulsions slightly coalesced under at pH 4.0 and 4.5 without added NaCl probably due to a relatively small amount of the surface protein load. Under all the other tested pH (4.0–7.0) and NaCl (0–100 mM) conditions, the OB-stabilized emulsions were stable against coalescence because of the improved surface load. These results suggest that OBs can be widely applicable for various food emulsions as a potential eco-friendly emulsifier with the appropriate formulation of acid and salt.