Effect of water activity on the stability of bixin in an annatto extract-microcrystalline cellulose model system

The influence of water activity on the stability of bixin in an annatto extract-micro-crystalline cellulose model system during storage at 21 ± 1 °C in the presence or absence of light and/or air was investigated. The water adsorption characteristic of the model system was determined. The samples were stored in desiccators containing saturated salt solutions for water activities of 0.33 to 0.97 and after equilibrium was reached, the samples were stored in the presence or absence of air and/or light. The degradation of bixin in every condition tested followed a first-order reaction. By comparing half-lives, bixin was observed to be more stable at intermediate/higher water activities.