Dose‐response Effects of Soybean Oil in Salad Dressing upon the Bioavailability of Carotenoids/Fat‐soluble Vitamins in Salad Vegetables

Abstract

Research is needed to quantify the dose effect between added vegetable oil and carotenoid/fat‐soluble vitamin absorption from vegetables. The objectives were to evaluate the dose‐response relation between the amount of soybean oil in salad dressing and the absorption of: 1) carotenoids, phylloquinone, and tocopherols in salad vegetables; 2) retinyl palmitate formed from the provitamin A carotenoids, α‐ and β‐carotene. Women (n = 12) each consumed 5 equivalent salads containing grated carrots, cherry tomatoes, romaine lettuce and spinach. The salads with salad dressings containing 0, 2, 4, 8, or 32 g phylloquinone‐ and tocopherol‐stripped soybean oil were consumed in randomly assigned order and separated by ≥ 2 wk. The plasma chylomicron fraction was isolated from blood samples collected at baseline and 2, 3.5, 5, 7, and 9.5 h postprandially. Across the entire 0 – 32 g range, the amount of soybean oil in salad dressing was linearly related to the plasma chylomicron area under the curve (AUC) values for α‐carotene, lycopene, phylloquinone, and retinyl palmitate. Across a more limited 0 – 8 g range of soybean oil, there was a linear increase in the chylomicron AUC values for β‐carotene. The absorption of all carotenoids and fat‐soluble vitamins was highest with 32 g ingested oil (P < 0.002). For the carotenoids/fat‐soluble vitamins that showed a linear response, the slope β (soybean oil effect) varied widely between subjects. In conclusion, soybean oil in salad dressing promoted the absorption of all carotenoids and fat‐soluble vitamins from salad vegetables. For a large salad, maximal absorption required more than 8 g and up to 32 g or more of soybean oil. Linear models could be used to predict the relation between the amount of soybean oil and the absorption of α‐ and β‐carotene, lycopene, and phylloquinone, as well as that of the provitamin A conversion product, retinyl palmitate.Support or Funding InformationSupported by Unilever R&D, Vlaardingen, the Netherlands