Model for measuring light stability of photolabile substances in powder beds using spray dried bixin microcapsules

Abstract

Light stability of different spray dried microencapsulated powders containing the natural colorant bixin was evaluated for 30 days. The encapsulating materials evaluated were sucrose, maltodextrin, and mixtures including gum arabic and pectin as encapsulation enhancers. The photostability of two sets of encapsulated material was compared: one containing purified bixin, and one being an annatto extract composed of bixin and native carbohydrates. The photodegradation of bixin was monitored by vis-spectroscopy and HPLC. The observed degradation was 30–70 times slower compared to unprotected colorants. A model was established for describing the degradation process of the colorant in a solid particle form presented as powder beds. It was concluded that encapsulation in combination with light scattering by the matrix structure had a significant effect on the protection of the colorant. The overall enhancement of bixin stability towards UVA-visible light can be attained by microencapsulation through spray-drying. A correlation was observed between encapsulation efficiency and improved photostability of the colorant.