Improving the water solubility of Monascus pigments under acidic conditions with gum arabic.

BACKGROUND: Monascus pigments (Mps) are natural food colorants and their stability in acidic solutions is important for application in the food industry. This study aimed to evaluate the use of gum arabic (GA) as a stabilizer for maintaining the solubility of Mps in an acidic aqueous solution exposed to a high temperature, and to analyze the molecular interactions between GA and Mps. RESULTS: Mps dispersed (0.2 g kg-1 ) in deionized water at pH 3.0-4.0 without GA formed precipitates but remained in a stable solution in the presence of GA (1 g kg-1 ). The significant improvement of Mps water solubility under acidic conditions was attributed to the formation of Mps-GA complexes, as indicated by a sharp increase in the fluorescence intensity. The results on particle size, zeta potential, and transmission electron microscopy further suggested that molecular binding of Mps to GA, electrostatic repulsion, and steric hindrance of GA were contributing factors to preventing the aggregation of Mps in acidic solutions. A mechanistic model was presented for GA-Mps interactions and complex structures. CONCLUSION: GA was proven to be an effective stabilizer of natural food colorants in acidic solutions. © 2016 Society of Chemical Industry.