Utilization of Turmeric Leaf Phenolic Extracts as Natural Antioxidants in Emulsion Systems

This study evaluated the effect of turmeric leaf phenolic extract (TLP) on lipid oxidation and physicochemical properties of oil-in-water emulsions. The dried leaves were first extracted using hydroethanolic solvents (0, 30, 50, 70%, w/w ethanol), and the total phenolic content and antioxidant properties were evaluated. Then, TLP was incorporated into emulsions at concentrations of 0, 250, 500, and 1000 µM (0, 0.46, 0.92, and 1.84 mg extract/mL emulsion). The characteristics, including appearance, size, polydispersity index, charge, lipid oxidation, viscosity, and microstructure, were evaluated both before and after heating at 85 °C. The results showed that all emulsions were stable up to 6 h at 85 °C. All fresh emulsions were nanosized with high negative zeta potential (-45.59 to -48.76 mV). With longer incubation time (6 h), the size (264-523 nm) and polydispersity index (0.32-0.43) increased, and the zeta potential decreased (-29.34 to -31.78). The oxidation values after 6 h were highest for the control (16.33 meq/kg oil and 7.03 mg MDA/kg oil) and lowest for the 1000 µM TLP emulsion (7.20 meq/kg oil, 0.74 mg MDA/kg oil). The samples containing 500 µM BHT showed the lowest oxidation and were comparable to the 1000 µM TLP emulsion. The polymerization and oxidation of the oil increased the viscosity during incubation, and the droplet size increased as observed in the CLSM images. Finally, it can be concluded that turmeric leaves, a major agricultural waste, are a potent source of antioxidants, capable of preventing oxidation and preserving the physicochemical properties of emulsions.