The dose-response effects of the amount of oil in salad dressing on the bioavailability of carotenoids and fat-soluble vitamins in salad vegetables
The objectives of the study were to define the dose-response relation of the amount of added oil and: 1) the absorption of carotenoids, phylloquinone and tocopherols in salad vegetables and 2) the absorption of retinyl palmitate formed from the ingested provitamin A carotenoids, ¦Á- and ¦Â-carotene. Women (n = 12) each consumed 5 salads containing equivalent amounts of carrot, cherry tomato, romaine lettuce and spinach. The salads with salad dressings containing 0, 2, 4, 8 or 32 g tocopherol-stripped soybean oil were ingested in random order separated by ¡Ý 2 weeks. Blood samples were collected at baseline and 2, 3.5, 5, 7, and 9.5 h postprandially. Chylomicron fractions were extracted and analyzed by HPLC with coulometric array electrochemical detection. When the salads were ingested with 0 g oil, there was negligible absorption of ¦Á- and ¦Â-carotenes, lutein, lycopene, phylloquinone, retinyl palmitate, ¦Á- and ¦Ã-tocopherols. For ¦Á- and ¦Â-carotenes, lycopene, retinyl palmitate, and ¦Á- and ¦Ã-tocopherols, absorption was increased with each amount of oil compared with 0 g oil (P <0.05). Starting from 4 g oil, all analytes (¦Á-carotene, ¦Â-carotene, lutein, trans-lycopene, vitamin A, ¦Á-tocopherol, ¦Ã-tocopherol, and vitamin K1) showed significant increases in absorption compared with 0 g oil salad dressing. The absorption of each carotenoid and fat-soluble vitamin was highest with 32 g ingested oil (P < 0.002).