Chemical and Physical Stability of Astaxanthin-Enriched Emulsion-Based Delivery Systems

Astaxanthin (AST) is carotenoid that is considered to have many potential benefits for human health. However, its poor water-solubility and chemical instability hamper its use as a functional food ingredient. The present study evaluated the effects of storage temperature, pH, ionic strength, and light exposure on the physical and chemical stability of AST-enriched emulsions prepared using caseinate as emulsifier. The chemical degradation of AST increased with increasing temperature, but the emulsions remained physically stable (droplet diameter = 230 nm; ζ-potential = −40 mV) at all incubation temperatures (5–70 °C). Solution pH, ionic strength and light exposure had little impact on the chemical stability of AST, except at pH 4 and 5. Conversely, the emulsions were highly unstable to droplet aggregation at pH values near the isoelectric point of the caseinate. This work highlights the benefits and drawbacks of using caseinate-stabilized emulsions as delivery systems for AST in functional foods and beverages.