In vitro accessibility of provitamin A carotenoids in vegetables and fruits - Effects of different process and preparation methods and estimation of vitamin A activity

Doctoral thesis, 2004

Vitamin A deficiency is a major nutritional problem in many developing countries, caused chiefly by a diet with low retinol content. The bioefficacy of provitamin A carotenoids in plant foods is claimed to be insufficient to maintain a satisfactory vitamin A status. The aim of the present thesis was to estimate the vitamin A activity of provitamin A carotenoids in edible portions of fresh and differently processed vegetables and fruits. For this purpose an in vitro method that simulates human digestion was developed to measure the fraction of provitamin A carotenoids that is released for absorption (bioaccessible). Results showed that carrots contain high amounts of α- and β-carotene (468±11 and 1357±52 µg/g dry material) and that green leafy vegetables and fruits contain highly varying amounts of mainly β-carotene, 338-914 µg/g d.m. and 2-55 µg/g wet weight, respectively. Thermal processes such as cooking and sun drying green leaves lowered the β-carotene content significantly and the degree of ripeness was shown to have a strong effect on the β-carotene content of fruits. The in vitro accessible amount of β-carotene in carrots greatly increased when the particle size was reduced. Twenty-six percent of the β-carotene content was released during in vitro digestion of raw carrots, which increased 1.3 times when carrots were cooked. The addition of cell wall degrading enzymes to a carrot purée significantly reduced particle size distribution, measured by sieving, and correlated well with increased in vitro accessibility of α- and β-carotene. In general cooked green leaves released ≤10% of its β-carotene content (19-103 µg/g d.m.) and fruits >40% (0.4-11.5 µg/g w.w.). An addition of sunflower or red palm oil to the cooked green leaves increased the accessibility more than two fold, and the red palm oil itself contributed a large amount of accessible α- and β-carotene. To convert provitamin A carotenoids into retinol equivalents (RE) we assumed that in vitro accessible provitamin A carotenoids were completely absorbed and, in accordance with FAO/WHO recommendations, half the amount was converted into retinol. One portion of a vegetable relish cooked with oil as consumed by children then contain enough RE to cover the recommended safe daily intake level (RSDIL) of vitamin A, while vegetables cooked without oil will provide only between 12 and 47%. An edible portion of fruits might provide between 18 and 144% of the RSDIL of vitamin A for children.