Content and In Vitro Accessibility of Provitamin. A Carotenoids in Some Tanzanian Vegetables and Fruits Effects of Traditional Processing and Preparation, and Influence on Vitamin A Status

Doctoral thesis, 2003

Vitamin A deficiency is among the major nutritional problems in Tanzania as in many developing countries. It mainly affects children and pregnant and lactating women. The basic cause of this problem is related to the diet, which contains little preformed vitamin A and plant foods with a low content and bioavailability of provitamin A carotenoids. This thesis reports studies conducted to evaluate the content and bioavailability of provitamin A carotenoids in selected fruits and vegetables from Tanzania and to elucidate the effects of different processing and preparation methods. The vitamin A and provitamin A carotenoid status in pregnant women was assessed in relation to the dietary intake pattern of provitamin A carotenoids and after supplementation with cooking oil. Results showed that leafy vegetables contain high but variable amounts of all-trans-β-carotene (399-914 µg/g dry weight) and minor amounts of α-carotene, 9-cis- and 13-cis-β-carotene. Fruits contain variable amounts of all-trans-β-carotene (191-5502 µg/100g fresh weight) and some fruits have minor amounts of β-cryptoxanthin and lycopene. Open sun dried leafy vegetables had significantly (p<0.05) lower amounts of all-trans-β-carotene (53%) than the fresh vegetables, whereas vegetables dried in solar cabinets showed losses of only about 23%. Cooking caused variable losses (6-51%) in all-trans-β-carotene content of the vegetables. The bioaccessibility (amount available for absorption) of the provitamin A carotenoids was estimated with an in vitro digestion method that simulates conditions in the human gastrointestinal tract. The in vitro accessibility of all-trans-β-carotene was low (4-15%) in vegetables cooked without added oil. However, higher (2 to 5-fold) in vitro accessibility of all-trans-β-carotene was obtained in vegetables cooked with added cooking oil. An addition of red palm oil provided significant amounts of accessible provitamin A carotenoids due to its high content of α- and β-carotene. Conversion of the amount of accessible provitamin A carotenoids into retinol equivalents according to FAO/WHO recommendations revealed that a median portion of a vegetable relish as consumed by children provided 88 to 477% of the recommended safe daily intake level (RSDIL) of vitamin A. Portions cooked without oil provided only between 23 and 46%. The in vitro accessible all-trans-β-carotene in fruits varied between 7% and 100%, and an edible portion of fruit (150g) would provide between 27 and 216 % of the RSDIL of vitamin A to children. Consumption of preformed vitamin A by pregnant women was very low and higher plasma retinol levels were correlated (p=0.03) with higher intakes of vegetables with oil. Supplementation with red palm oil increased α- and β-carotene concentrations significantly (p<0.001) in both plasma and breast milk. The breastmilk retinol concentration tended to decrease from 1 to 3 months postpartum in the control group but was maintained in the groups given supplements of either red palm oil or sunflower oil.