The kinetics of the loss of all-trans retinol at low and intermediate water activity in air in the dark

All-trans retinol was suspended on a support of microcrystalline cellulose and stored in air in the dark after equilibration at water activities from 0.11 to 0.75. The loss of all-trans retinol was monitored by normal phase HPLC. The rate of loss could be satisfactorily described by first-order kinetics with respect to all-trans retinol (up to more than 50% loss). The rate increased with increasing water activity in the range 0.11–0.75 aw. Arrhenius activation energies were found to be in the range of 28–48 × 103 J mol−1. A correlation between enthalpy change and Gibbs free energy change indicated a chemical compensation effect in the range 0.11–0.66 water activity.