(77a) Morphological Stability of Microencapsulated Lipophilic Compounds By AFM Imaging

Micronutrients and nutraceuticals such as vitamins, carotenoids and polyunsaturated fatty acids (PUFAs) are essential for human and animal health and well-being. Fat-soluble vitamins, like Vitamin A, or PUFAs are often chemically instable (e.g. to oxidation, heat) and they cannot easily be added to a hydrophilic food environment like a beverage. Thus, such vitamins are mostly sold in microencapsulated product formulations to protect the active ingredient from the surrounding environment. The morphological stability of microencapsulated lipophilic compounds directly influences the long-term storage stability and performance in final applications. Thus, during the development of novel product formulations, the stability of the encapsulated active ingredient is typically monitored in time-consuming studies, storing the product formulations at different environmental conditions and assessing the concentration of the active ingredient at several time points. Here, a facile method to investigate the internal morphology and structural stability of microencapsulated vitamins has been successfully developed. The internal particle morphology of three commercial dry Vitamin A acetate formulations differing in their matrix composition (hydrocolloid/polysaccharide and plasticizer) was systematically characterized by atomic force microscopy (AFM). The evolution of the particle internal morphology after per-se storage at 25 and 40 °C for ten months was investigated. Furthermore, an accelerated stress test by in-situ heating and AFM imaging was developed. Surface roughness parameters from the AFM images were used to semi-quantitatively estimate the evolution of the particle internal microstructure, and thus the aging and destabilization of the lipophilic vitamin formulations. The influence of humidity level on the thermal morphological restructuring of one of the commercial samples was also investigated. This study has shown that such AFM investigations of microparticles are a novel analytical tool to rapidly estimate the physical stability of the lipophilic vitamin dried emulsions.

Mougin, K., A. Bruntz, D. Severin and A. Teleki, "Morphological stability of microencapsulated vitamin formulations by AFM imaging," Food Structure 9, 1-12 (2016).