Encapsulation and solubilization of antioxidants gallic acid and ethyl, propyl and butyl gallate with B-cyclodextrin

We investigated the formation of inclusion complexes of the antioxidants (AOs) gallic acid, GA, and its hydrophobic derivatives ethyl (EG), propyl (PG) and butyl (BG) gallate with β-cyclodextrin (β-CD) by employing the UV spectral shifts method and, for the sake of comparisons, a modified phase-solubility method that exploits the use of a competitive guest molecule (acetonitrile, ACN) that completely removes the antioxidants from the CD cavity and, at the same time, keeps them in solution. The modification of the phase-solubility method is a consequence of the significant solubility of the AOs in water (S_GA > S_EG > S_PG > S_BG). The binding constants for GA and EG could not be determined because of the negligible effect of β-CD in their spectrum. PG and BG form 1:1 inclusion complexes and the values for the binding constants, K_PG and K_BG, respectively, could be determined, K_PG = 105 ± 2 M^− 1 and K_BG = 200 ± 15 M^− 1. Very similar values were obtained by the modified phase-solubility method, indicating that the use of ACN as competitive guest molecule is a good choice that opens the possibility of using the phase-solubility method to molecules having significant water-solubility. The results may be of interest to the food industry because inclusion of phenolic antioxidants, which are widely employed to minimize the oxidation of lipid-based foods, can substantially improve their efficiency.