Stability of oil-in-water emulsions with eggplant flesh pulp (Solanum melongena L.) emulsifier: Effects of storage time, pH, ionic strength, and temperature

Abstract

In this study, we investigated the stability of oil-in-water emulsions prepared using eggplant flesh pulp (EFP) as natural emulsifier. The effects of time and environmental stresses on the stability of emulsions with different EFP concentrations were evaluated using the creaming indices (CIs), particle sizes, and zeta potentials of the emulsions. The emulsions with EFP concentrations of up to 1.50% remained stable for at least 90 days. The CIs, mean particle diameters (MPDs ]d_3,2 ]), and zeta potentials of the emulsions with adequate EFP concentrations remained unchanged in the pH range of 3-9. Microstructure observations revealed that flocculation occurred for the emulsion with an EFP concentration of 1.50% at pH 3, whereas flocculation and coalescence occurred in the emulsion with a low EFP concentration of 0.50%. Upon increasing the concentration of NaCl from 0 to 0.5 M, the MPDs (d_3,2 ) of the emulsions with EFP concentrations of 1.00% and 1.50% remained nearly constant (57 and 48 µm, respectively). Moreover, the MPDs (d_3,2 ) and zeta potentials of the emulsions with EFP concentrations of 1.00% and 1.50% did not change significantly upon increasing temperature from 4 to 100°C. Hence, the emulsions with adequate EFP concentrations presented long storage times and were stable under various environmental stresses. Our results indicate that EFP is an effective and inexpensive emulsifier that can confer emulsions long-term storage stability and good resistance to environmental stresses. PRACTICAL APPLICATION: Eggplant, which is a common crop, is a rich source of natural materials. In this study, eggplant flesh pulp (EFP) was prepared via mechanical homogenization and its emulsifying properties for oil-in-water emulsions were evaluated. Our results demonstrated that the EFP-stabilized oil-in-water emulsions featured long storage times and were stable under environmental stresses (pH, ionic strength, and temperature). These properties render EFP-stabilized emulsions suitable as delivery systems for encapsulating and releasing nonpolar active ingredients in food products.

Keywords: eggplant flesh pulp; emulsion stability; polysaccharide emulsifier.