Kinetic studies of the thermal degradation of sulforaphane and its hydroxypropyl-β-cyclodextrin inclusion complex

Abstract

Sulforaphane (SF) has been of increasing interest for nutraceutical and pharmaceutical industries due to its anti-cancer effect, but it is very sensitive to changes in the temperature and pH. In the present work, pure SF and inclusion complex of SF with hydroxypropyl-β-cyclodextrin (SF/HP-β-CD) were prepared, the depletion rates of SF and SF/HP-β-CD were investigated at temperatures of 60, 75, 82 and 90°C and pH values of 2.2, 3.0, 4.0, 5.0 and 6.0. The results showed that SF and SF/HP-β-CD were more stable at lower pH values and temperatures, and SF/HP-β-CD was more stable than SF. The SF and SF/HP-β-CD degradation was observed to follow first order kinetics, and the temperature-dependent rate constants for SF and SF/HP-β-CD inclusion complex in aqueous solution were well described by the Arrhenius equation with corresponding activation energies of 70.7 to 94.5kJ/mol, depending on the pH values. Finally, models to describe the retention ratio of SF and SF/HP-β-CD at different pH values, depletion time and temperatures were proposed.