Dietary Factors That Affect the Bioavailability of Carotenoids

The relative bioavailability of ß-carotene from vegetables compared with purified ß-carotene ranges between 3 and 6% for green leafy vegetables, 19 and 34% for carrots and 22 and 24% for broccoli (4–9). In one study, broccoli and green peas induced a larger ß-carotene response in plasma than whole-leaf and chopped spinach, despite a 10 times lower ß-carotene content in the former vegetables (9). In another study, ß-carotene from fruits was found to be 2.6–6 times as effective in increasing plasma concentrations of retinol and ß-carotene than green leafy vegetables (10). These differences may result from differences in intracellular location of carotenoids. In leaves, they are present in chloroplasts, whereas in fruits, and possibly also other parts of the plant, carotenoids are located in chromoplasts. This has led to the speculation (10) that chloroplasts may be less efficiently disrupted in the intestinal tract than chromoplasts.  

http://jn.nutrition.org/content/130/3/503.full