Ca2+ Cross-Linked Alginic Acid Nanoparticles for Solubilization of Lipophilic Natural Colorants

The increased tendency toward healthy lifestyles has promoted natural food ingredients to the detriment of synthetic components of food products. The trend followed into the colorant arena, with consumers worried about potential health problems associated with synthetic colorants and demanding food products that use natural pigments. The goal of this study was to entrap a lipophilic natural pigment (beta-carotene) in a water-soluble matrix made of Ca2+ cross-linked alginic acid, to allow its use as a colorant in water-based foods. The effects of different synthesis parameters such as type of solvent, alginic acid concentration, and calcium chloride concentration on nanoparticle characteristics (i.e., size, zeta potential, and morphology) were evaluated. The particle stability was assessed by measuring aggregation against pH, oxidation, and particle precipitation as a function of time. The particle synthesized measured 120-180 nm when formed with chloroform and 500-950 nm when synthesized with ethyl acetate. The particles were negatively charged (-70 to -80 mV zeta potential) and were stable at pH values ranging from 3 to 7. The presence of calcium was prevalent on the particles, indicating that the divalent ions were responsible for cross-linking lecithin with alginic acid and forming the matrix around the beta-carotene pockets. The addition of calcium increased nanoparticle density and improved beta-carotene protection against oxidation. It is concluded that the method proposed herein was capable of forming water-soluble nanoparticles with entrapped beta-carotene of controlled functionality, as a result of the type of solvent and the amounts of alginate and Ca2+ used.