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shown to increase bioactivity. In a study by Wang and associates, curcuminloaded nanoemulsions were topically applied on mouse ear edema to reduce growth of tumors. The authors of the study reported that application of nanoemulsion (d ~ 70 nm) led to an 85% reduction in tumor tissue compared to a 43% reduction seen in the topical application of a macroemulsion (d ~ 500 nm) (Wang et al., 2008). III.A.2. Functional properties of nanoemulsions As mentioned, nanoemulsions may have functional properties such as appearance, physical and chemical stability, texture, and activity of encapsulated bioactive compounds that differ from that of conventional emulsions. This has raised interest in using nanoemulsions as carriers of functional lipids (e.g. antioxidants, flavors, colors, and antimicrobials). It should be noted though that no one single critical size exists at which all these functional properties change simultaneously. Instead, each one has a specific size dependence that may differ from that of other functional properties. In some cases, the functionality may change dramatically over a narrow size range, as is the case for optical properties of the emulsion (i.e. emulsion changes from whitemilky opaque to completely transparent when mean droplet diameters decrease from 120 to ca. 80 nm). For other properties, such as stability of the emulsion to gravitational separation, this change is more gradual and substantial improvements may be seen at sizes below 300 nm (Figure 24.2). Appearance. The scattering intensity of droplets decreases as their size decreases relative to the wavelength of light (McClements, 2002a, b). Consequently, the appearance of emulsions is strongly dependent on droplet size, and emulsions become transparent when the size of the droplet falls below a critical diameter (d < 90â&#x20AC;&#x201C;100 nm). Nanoemulsions are thus easily distinguishable from conventional emulsions and may be quite attractive to beverage manufacturers trying to avoid introduction of turbidity with addition of antimicrobial-carrying emulsions. Gravitational stability. The stability of emulsions to gravitational separation (creaming or sedimentation) increases as droplet size decreases, with creaming velocity proportional to d2. When droplet size falls below a critical value (d ~ 100 nm), emulsions become completely stable to creaming or sedimentation because the effects of Brownian motion dominate gravitational effects (McClements, 2005a). Nanoemulsions can thus be kinetically stable for many years, a property that makes them again very attractive to food manufacturers. Aggregation stability and rheology. Emulsion stability to flocculation and coalescence depends strongly on droplet size because of the size dependence of the droplet collision (e.g. frequency and efficiency). The