Increasing photostability and water-solubility of carotenoids: synthesis and characterization of β-carotene-humic acid complexes

Carotenoids are a group of phytochemicals that are recognized as playing an important role in the prevention of several degenerative diseases due to their antioxidant activity. The low water-solubility and poor photostability of b-carotene, a potentially important dietary antioxidant, prompted us to investigate b-carotene complexes able to increase its water solubility as well as its photostability in aqueous solution. In this work we have used humic acid in order to synthesize b-carotene–humic acid complexes in different ratios. Complexes were characterized by FT-IR and DSC. b-Carotene determination were performed by HPLC and antioxidant activity of b-carotene, humic acid and the complexes were determined by the TEAC method. The formulation b-carotene–humic acid 2:1 showed the highest photostability and water solubility. The antioxidant activity of the complexes was about 20 times lower than ‘‘free’’ b-carotene, suggesting a decreased chemical reactivity of the carotenoid in the complex. We showed that complexation of b-carotene with humic acids was able to increase its water solubility and photostability, and to affect the antioxidant activity of b-carotene after inclusion in HAs. This work provides a useful tool to avoid antioxidants photodegradation and oxidation by radicals, thus maintaining their biological activity.