Article pubs.acs.org/JAFC
Physical and Chemical Stability of Curcumin in Aqueous Solutions and Emulsions: Impact of pH, Temperature, and Molecular Environment Mahesh Kharat,† Zheyuan Du,† Guodong Zhang,† and David Julian McClements*,†,§ †
Department of Food Science, University of MassachusettsAmherst, Amherst, Massachusetts 01003, United States Department of Biochemistry, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
§
S Supporting Information *
ABSTRACT: The utilization of curcumin as a nutraceutical in food and supplement products is often limited because of its low water solubility, poor chemical stability, and low oral bioavailability. This study examined the impact of pH, storage temperature, and molecular environment on the physical and chemical stability of pure curcumin in aqueous solutions and in oil-in-water emulsions. Unlike naturally occurring curcuminoid mixtures (that contain curcumin, demethoxy-curcumin, and bisdemethoxycurcumin), pure curcumin was highly unstable to chemical degradation in alkaline aqueous solutions (pH ≥7.0) and tended to crystallize out of aqueous acidic solutions (pH 85% of curcumin was retained by emulsions stored under acidic conditions (pH 24 h at 37 °C. Consequently, this type of surfactant was unsuitable for the long-term storage studies used in this research. Further experiments were therefore carried out using oil-in-water emulsions prepared using Tween 80 as the surfactant because these remained physically stable when stored at 37 °C. The initial curcumin content in the stock emulsion (40 w/w % MCT, pH 5.0) was around 0.38 mg/mL, which was close to the original amount of 0.39 mg/mL of curcumin added, that is, 1 mg curcumin/g MCT. This result suggested that curcumin was not degraded or lost during the preparation of the emulsions by homogenization. The stock emulsions were diluted with buffer solutions to create a series of emulsions with the same initial curcumin level (0.285 mg/mL) and oil content (30% MCT), but different pH values (3.0−8.0). There was an appreciable decrease in the curcumin concentration remaining in the neutral-alkaline emulsions (pH ≥7.0), but little change in the acidic emulsions (pH
