beta-Carotene Absorption and Metabolism

beta-Carotene is the most potent provitamin A carotenoid and has potential antioxidant properties. A better understanding of bioaccessibility, absorption, and metabolism of beta-carotene may help alleviate symptoms and diseases related to vitamin A deficiency. To better understand beta-carotene absorption, we have studied beta-carotene in fruits and vegetables, its bioaccessibility from food sources through in vitro digestion, and absorption by humans in a controlled feeding study. We also studied the metabolism of beta-carotene by measuring the presence of beta-apocarotenoids in foods, mice, and humans, as well as the conversion of newly absorbed beta-carotene to its retinoid metabolites.;The first study was conducted to determine the beta-carotene content and its bioaccessibility/bioavailability in orange-fleshed melons. Orangedew melons have less consumer risk for food borne illness and have significantly more beta-carotene than cantaloupes grown under the same conditions. Micellerization of beta-carotene during simulated digestion of orange-fleshed melons was approximately 3.2%. We also detected and quantified beta-apocarotenoids in the melons.;The second study was conducted to investigate in humans the variability in beta-carotene absorption and its conversion to vitamin A and to compare the efficiency of absorption of beta-carotene with that of cholesterol. Ten men consumed a 5 mg dose of deuterium labeled beta-carotene (d8-betaC), with 6 subjects repeating the dose 2 months later. For this study, we developed a method that provides a simple sample extraction for both retinoids and beta-carotene that included minimal sample handling, and allows us to detect and quantify newly absorbed d8-beta-carotene, as well as its d4-retinyl ester metabolites. The method allowed us to accurately measure d8-beta-carotene absorption, and its extent of conversion to d4-retinyl esters. There was marked inter-individual variability in beta-carotene absorption and conversion to retinyl-esters. In contrast, intra-individual variability in beta-carotene absorption and its conversion to retinyl esters was low. beta-Carotene and cholesterol may share specific intestinal transporters, but there was no correlation between an individual's efficiency of absorption of beta-carotene and his efficiency of absorption of cholesterol (r=-0.09; p=0.81).;The third study was conducted to determine the beta-apocarotenoid levels in commonly consumed products containing beta-carotene, such as fruits and vegetables, as well as in murine serum and liver, and human plasma. beta-Apocarotenoids are present in our diets but their absorption, metabolism, and biological roles are largely unknown. Using HPLC-MS, we were able to detect and quantify beta-apo-13-carotenone, beta-apo-14'-carotenal, beta-apo-12'-carotenal, beta-apo-10'-carotenal, beta-apo-8'-carotenal and beta-carotene in several fruits and vegetables. In vitro digestion studies have shown that beta-apocarotenoids are micellerized to a greater extent than beta-carotene. We have shown here that they are present in considerable amounts in the diet and that they may be absorbed in addition to being generated in vivo. We have also shown that these beta-apocarotenoids are present in the liver and serum of beta-carotene fed mice and in human plasma. We have uncovered new aspects of beta-carotene absorption and metabolism that should be considered in future beta-carotene studies, such as conversion of beta-carotene to specific retinyl esters, low intra-individual variability of beta-carotene absorption, and the presence of beta-apocarotenoids in all beta-carotene containing samples.