Exploitation of maize germ for the preparation of a stable oil-body nanoemulsion using a combined aqueous extraction–ultrafiltration method

A natural oil-in-water (o/w) nanoemulsion was prepared from maize germ flour by initially extracting the germ oil bodies with water at pH 9 followed by application of ultrafiltration to concentrate the dilute extract. The resulting o/w emulsion with an oil and protein content of 5 and 3%, respectively, was characterized by a mean surface-volume diameter of 155 nm with 90% of the droplets having a size lower than 100 nm. The very low oil-body size indicated that the application of ultrafiltration to the initial extract prevented the appearance of coalescence phenomena allowing the oil bodies in the resulting concentrated dispersion to retain their natural integrity. The physical stability of the natural emulsion was evaluated both under quiescent storage conditions as well as following extensive heat or freezing treatment. The findings on physical stability are discussed in terms of the presence in the dispersion of both oil-body surface proteins as well as of co extracted non-adsorbed exogenous germ proteins.