In vitro screening of relative bioaccessibility of carotenoids from foods

Carotenoids are lipophilic pigments in plant foods that are of particular interest as precursors of vitamin A, a nutrient required for vision, cell differentiation, and the immune system. In order to mediate such activities, carotenoids and their metabolites must be absorbed for delivery to tissues. Unlike many other dietary lipids, the efficiency of carotenoid absorption is typically inefficient, being affected by food matrix, style of processing, other dietary components, and nutritional and physiological status. Thus, reliable prediction of carotenoid bioavailability is problematic. We have developed a relatively simple and cost effective procedure to study the potential bioavailability, i.e., the bioaccessibility, of carotenoids. The method involves simulated oral, gastric and small intestinal digestion of test samples to access the efficiency of incorporation into micelles, an obligatory step for absorption of lipophilic compounds. The model can be further expanded by adding micelles generated during small intestinal phase of digestion to monolayers of Caco-2 human intestinal epithelial cells to investigate apical uptake, cellular metabolism and transepithelial transport of carotenoids. Recent work by Borel and associates has demonstrated that the relative bioaccessibility of carotenoids observed in vitro is highly correlated with in vivo observations and results from bioavailability trials with human subjects. Results from recent studies using the in vitro model to screen relative bioaccessibility of beta-carotene in various cultivars of cassava, impact of amount and types of fatty acyl groups in triglycerides on micellarization of carotenoids, and the mechanism of digestion and intestinal cell uptake of xanthophyll esters are presented.