Stability of emulsions for parenteral feeding: Preparation and characterization of o/w nanoemulsions with natural oils and Pluronic f68 as surfactant M. Wulff-Pe ´rez, A. Torcello-Go ´ mez, M.J. Ga ´ lvez-Ruı ´z, A. Martı ´n-Rodrı ´guez * Biocolloid and Fluid Physics Group, Department of Applied Physics, Faculty of Sciences, University of Granada, 18071 Granada, Spain article info Article history: Received 11 May 2008 Accepted 30 September 2008 Keywords: Soybean Sesame and olive oils Pluronic F68 Nanoemulsions Depletion–flocculation abstract For hydrophobic bioactive compounds, poor water solubility is a major limiting factor for their use in different applications in the field of food industry or pharmacy. For this reason they are administrated as emulsions, in which the substance is dissolved in an organic compound, which is dispersed in an aqueous phase as droplets stabilized by a surfactant. It has been demonstrated that the colloidal stability of the nanoemulsion formulations can be precisely controlled by the chemical structure of the interface. In this paper, a promising delivery system has been studied. As surfactant, we have used the amphiphilic uncharged tri-block copolymer Pluronic F68, and natural oils from soybean, sesame and olive as the organic phase. The nanoemulsions were prepared by ultrasonication, and their stability at different synthesis conditions such as ultrasound power and surfactant concentration has been studied by monitoring backscattering using a Turbiscan. The more stable emulsions have been characterized by DLS, and their droplet size was below 500 nm, which has resulted very appropriate for parenteral adminis- tration. A destabilization of the system always takes place above certain surfactant concentration. This phenomenon was described as a depletion–flocculation effect caused by non-adsorbed micelles. This destabilization was modelled by adding to the DLVO interaction energy a contribution addressing the force between two spherical particles in the presence of non-adsorbing spherical macromolecules. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Oil-in-water emulsions are important vehicles for the delivery of hydrophobic bioactive compounds into a range of food products, nutraceuticals, cosmetic compounds, and drugs. Many of their properties are determined by the droplet size and size distribution, e.g., small droplet sizes in general lead to a creamier mouth feel and greater emulsion stability (McClements, 2004). Depending on droplet diameter, emulsions can be divided into mini/nano- (20–500 nm) and macro-emulsions (0.5–100 mm). Nanoemulsions, unlike microemulsions, are not thermodynamically stable but kinetically, and they do not form spontaneously. However, the long- term physical stability of nanoemulsions (with no apparent floc- culation or coalescence) makes them unique (Tadros, Izquierdo, Esquena, & Solans, 2004). Besides, they do not require a large amount of surfactant as microemulsions do; they can be prepared with reasonable surfactant concentrations: for a 20% o/w nano- emulsion, a surfactant concentration in the region of 5–10% (w/w) will be sufficient (Tadros et al., 2004). To prepare nanoemulsions a large amount of energy is required. Low-energy emulsification methods involve transitional inversion induced by changing factors that affect the hydrophilic–lipophilic balance (HLB), e. g. temperature and/or electrolyte concentration, in order to transform an o/w emulsion into a w/o emulsion or vice versa (Tadros et al., 2004). However, they have several limitations, such as their requiring a large amount of surfactant, a careful selection of surfactant–cosurfactant combination, and careful control of the temperature. Yet, they are inapplicable to large-scale industrial productions. On the other hand, high-energy emulsifi- cation methods such as high-pressure homogenizers and high shear motionless mixers have several advantages that are appli- cable to industrial operations. Those advantages included the flexible control of droplet size distributions and the ability to produce fine emulsions from a large variety of materials (Seek- kuarachchi, Tanaka, & Kumazawa, 2006). Studies comparing ultrasonic emulsification with rotor–stator dispersing have found ultrasound to be competitive or even supe- rior in terms of droplet size and energy efficiency (Canselier, Del- mas, Wilhelm, & Abismaı ¨l, 2002). The same studies also have shown that microfluidization has been found to be more efficient than ultrasound, but less practicable with respect to production cost, equipment contamination. Comparing mechanical agitation to ultrasound at low frequency, Tadros et al. (2004) found that for * Corresponding author. Dpto. Fı ´sica Aplicada, Universidad de Granada, Facultad de Ciencias, Fuentenueva s/n, Granada 18071, Spain. Tel.: þ34 958240017; fax: þ34 958243214. E-mail address: amartinr@ugr.es (A. Martı ´n-Rodrı ´guez). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd 0268-005X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2008.09.017 Food Hydrocolloids 23 (2009) 1096–1102