IN VITRO AND IN VIVO EVALUATION OF BIOACCESSIBILITY AND BIOAVAILBILITY OF VITAMIN D₃ ENCAPSULATED WITHIN RE-ASSEMBLED CASEIN MICELLES

The development of effective natural carriers to protect and enhance bioavailability of ingested nutraceuticals remains a major challenge. The use of novel protein-based nanovehicles for lipophilic nutraceuticals raises important questions regarding the bioavailability of the entrapped lipophilic nutraceutical, and its absorption mechanism in the GI tract in the absence of fat. To examine these questions, we focused on vitamin D₃ (VD₃) loaded within re-assembled casein micelles (rCM) as a model system, which had been demonstrated to provide significant protection to entrapped hydrophobic nutraceuticals. rCM were found to be well reconstituted after freeze drying, provided prior addition of maltodextrin. Semi-dynamic in vitro gastro-duodenal digestion of the VD₃ loaded rCM was performed to study VD₃ retention and rCM digestibility. HPLC analysis of digesta revealed that VD₃ retention is significantly higher when it is encapsulated in rCM compared to free VD₃ (90% and 20% after 3h respectively). SDS-PAGE analyses of digesta samples revealed that VD loading does not significantly affect enzymatic digestion of the rCM in the stomach.

A large scale (94 healthy volunteers) single high dose ingestion double-blind placebo-controlled randomized clinical trial was performed to examine how the bioavailability of VD₃ is affected by its delivery in protein nanoparticles, rather than in the fat, and in its presence/absence. As a model food, 0% fat yoghurt (the most widely consumed nonfat milk product) was chosen. The results indicated that the bioavailability of VD₃ in the protein based nanoparticles in the absence of fat did not significantly differ (p>0.1) from its bioavailability in fat. Overall, this work provides pioneering evidence that protein-based nano-vehicles present an excellent alternative to fat for delivery of hydrophobic nutraceuticals in foods.