Effects of FeII, tannic acid, and pH on the physicochemical stability of oil body emulsions

This study examined the effects of solution pH (3.0, 5.0, and 7.0), FeII, and tannic acid (TA) on oil body (OB) emulsions and monitored changes in emulsion particle size, zeta potential, appearance, microstructure, and oxidation stability over 14 days of storage at 37 °C. The chelation efficiency, zeta potential, and fourier-transform infrared spectroscopy results showed that the ability of TA to chelate FeII and the absolute charge of TA-Fe complexes increased with the pH. In addition, the distribution of these complexes in the emulsions was influenced by their electrostatic and hydrogen bonding interactions with the OB. At pH 3.0 and 5.0, the TA-Fe and OB emulsion particles attracted each other, resulting in droplet flocculation. At pH 7.0, the TA-Fe and OB emulsion particles carried the same (negative) charge, and had little effect on physical stability of OB emulsions. TA generally inhibited the oxidation of OB emulsions but promoted the concentration of the primary and secondary oxidation products (61.48 mmol/kg and 50.5 μmol/kg, respectively) of FeII-containing emulsions at pH 3.0. The obtained results provide new insights into the efficacy of TA as a natural antioxidant for emulsified foods and thus pave the way to increasing their quality and shelf life.