Comparison of Emulsion and Nanoemulsion Delivery Systems: The Chemical Stability of Curcumin Decreases as Oil Droplet Size Decreases

Abstract

The water dispersibility, chemical stability, and bioaccessibility of curcumin, a labile hydrophobic nutraceutical, can be enhanced by incorporating it inside the oil droplets of oil-in-water emulsions or nanoemulsions. In these multiphase systems, the curcumin remains relatively stable to degradation when surrounded by oil but degrades rapidly when surrounded by water. We hypothesized that the size of the lipid droplets would therefore impact the stability of encapsulated curcumin by altering the surface area of oil exposed to water. The effect of droplet surface area on the kinetics of curcumin degradation was therefore studied by producing emulsions with different mean droplet diameters (d 32) and therefore different specific surface areas (A S): large (d 32 = 20.9 μm; A S = 300 m2 kg–1); medium (d 32 = 2.53 μm; A S = 2500 m2 kg–1); small (d 32 = 0.26 μm; A S = 24,000 m2 kg–1); and very small (d 32 = 0.083 μm; A S = 80,000 m2 kg–1) emulsions. All the emulsions initially had milky-yellow appearances and were relatively stable to aggregation during the course of the experiments. However, rapid creaming was observed in the large and medium emulsions because of their relatively large droplet size. The emulsions all exhibited some color fading during storage, with the rate of curcumin degradation increasing with decreasing droplet size. For instance, the percentage of curcumin remaining in the emulsions after 17 days storage was 91.4 ± 1.5 > 77.3 ± 6.6 > 66.7 ± 1.9 ≫ 30.6 ± 2.8% for the large, medium, small, and very small emulsions, respectively. The more rapid chemical degradation of the curcumin in the smaller droplets can be attributed to the fact that curcumin exchange between the interior and exterior of the droplets occurs more rapidly as the droplet dimensions decrease. Our results indicate that the droplet size plays a critical role in the degradation of curcumin encapsulated in emulsions, which may have important consequences for the formulation of curcumin-enriched foods and beverages with enhanced bioactivity. In particular, it suggests that emulsions are more effective at chemically stabilizing curcumin than nanoemulsions.

Application of Advanced Emulsion Technology in the Food Industry: A Review and Critical Evaluation

“…Another promising application of nanoemulsions is to enhance the bioaccessibility and bioavailability of hydrophobic bioactive compounds [18]. In vitro studies using simulated gastrointestinal models have shown that nanoemulsions can increase the bioaccessibility of β-carotene [19,20], lycopene [21], resveratrol [22], curcumin [23][24][25][26], and 5-demethylnobiletin [27]. Information about the preparation procedures and droplet sizes of nanoemulsions used for different applications is summarized in Table 1.…”

Progress in Colloid Delivery Systems for Protection and Delivery of Phenolic Bioactive Compounds: Two Study Cases—Hydroxytyrosol and Curcumin

“…In another study, Kharat and co-workers [ 116 ] considered the effect of droplet surface area on the kinetics of CUR degradation using emulsions with different mean droplet diameters. The authors observed that the rate of CUR degradation increased with decreasing droplet size, and they concluded that this was attributable to the fact that CUR exchange between the interior and exterior was faster in small droplets.…”

Innovative Delivery Systems Loaded with Plant Bioactive Ingredients: Formulation Approaches and Applications

“…The authors postulated that droplet size plays the most important role in the degradation of curcumin encapsulated in emulsions; a fact that may affect its bioactivity in various food and beverage products. Resveratrol’s chemical stability may be increased by its incorporation into nanoemulsion compared with that of free (aqueous or ethanolic extract) resveratrol [ 358 ]. Phytosterols, such as stigmasterol, β-sitosterol and campesterol, have been proved to inhibit the absorption of dietary cholesterol but demonstrate degradation issues related to oxidation [ 359 ].…”