Complexation of olive oil antioxidant with cyclodextrins

Oleuropein (OLE) is a major constituent of the olive leaf and green olives (Olea europaea). It has antioxidant and therapeutic properties and is valued as a medicinal component. The molecule is a complex phenolic compound constituted by a heterosidic ester of the elenolic acid and dihydroxy ethanol. This work concerns the determination of the inclusion complex constants between OLE and cyclodextrins (CDs). The methodology was based on the competition of two guests for the CD cavity, one being a dye and the other OLE. The dye used was methylorange (MO) and pH 3 was selected, since MO molar absortivity at 500 nm is maximum. Solutions of MO 0.045 × 10 mol L, OLE 0.75 × 10 mol L and α-CD, 0 to 0.625 × 10 mol L, or β-CD, 0 to 5.0 × 10 mol L, with citrate buffer 0.05 mol L were used for determining the absorbance values. From these data and by appropriate mathematical modeling, thorough the supposition of equilibrium between the complexes, the constant of formation of OLE:CD complexes were obtained. The resulting complexation constants are: for OLE:α-CD K=1352.4 M (R=0.9975) and for OLE:β-CD K=1827.9 M (R=0.9991). These results show that OLE has a greater affinity for β-CD than for α-CD and given the relatively high constants, OLE:β-CD complexes have potential for giving longer shelf lives for OLE food and medicinal additive preparations. Solid forms of the inclusion complexes of oleuropein in cyclodextrins were prepared by the methods of kneading and physical mixture, and then characterized by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC), showing higher degradation temperature for the complexes. The best preparation was obtained with complexation of oleuropein and β-CD at 1:2 molar ratio. Complexation is advantageous since it protects oleuropein from higher temperatures, which is useful in food and pharmaceutical applications.