The aim of this study was to study the effect of different physicochemical factors on the stability of curcumin in oil-in-water emulsions. Curcumin was incorporated in aqueous or emulsions systems and its stability was measured over time. Pure curcumin degraded quickly in alkaline aqueous solutions and crystallized out in acidic aqueous environments. Its water dispersibility and chemical stability were improved by incorporation into oil-in-water emulsions. Curcumin retention was >85% at pH < 7.0, whereas 62, 60, and 53% were retained by emulsions stored at pH 7.0, 7.4, and 8.0, respectively (37 °C, 1 month). It was found that curcumin transfer could occur in such a system from the protective oil phase to the detrimental aqueous phase causing curcumin degradation in emulsions. It was also found that degradation occurs at a faster rate as the droplet surface area increased. This may be mainly due to increased curcumin transfer from oil to the aqueous phase and/or enhanced interfacial exposure to hydroxyl ions, and oxygen responsible for chemical degradation. Finally, the extent of curcumin degradation in emulsions fabricated using four different emulsifiers decreased in the following order: saponins >> gum arabic ≈ casinate ≈ Tween 80 after storage at 55 °C for 15 days, suggesting that curcumin degradation was accelerated in saponin stabilized emulsions. This study established that the stability of curcumin is affected by various physicochemical parameters, and it may be important to optimize emulsions with respect to emulsifier type, mean droplet size to achieve higher curcumin retention.
