Provitamin A Carotenoids in Orange-Fleshed Sweet Potato

Licentiate thesis, 2008

Vitamin A deficiency is a major nutritional disorder in a large number of developing countries. The disorder is mainly caused by an inadequate intake of preformed vitamin A and provitamin A carotenoids from the diet. It is also recognized that vitamin A deficiency and iron deficiency tend to coexist in many population groups. On the other hand, recent studies have indicated that vitamin A and β-carotene might have a positive effect on iron absorption. The aim of the present thesis was to evaluate orange-fleshed sweet potato (OFSP) as a food source of provitamin A carotenoids and to study the interactive effects between β-carotene and iron on their respective uptake in an in vitro model. The effects of various processing and drying methods on the retention of all-trans-β-carotene in OFSP were investigated with a high-performance liquid chromatography (HPLC) method. The interactive effects of a simultaneous uptake of β-carotene from micelles and iron were studied using a Caco-2 cell model. Results showed that OFSP contains considerable amounts of all-trans-β-carotene (108-315 μg/g dry matter) and that the amount is highly dependent on the variety. Traditional preparation methods resulted in moderate losses of all-trans-β-carotene (approximately 78% of the all-trans-β-carotene content was retained) and the effects of boiling, steaming, and deep-frying were similar. These results demonstrate that one 100 g ready-to-eat portion of four out of the seven OFSP varieties in the present study would provide enough all-trans-β-carotene to completely cover the daily vitamin A requirements for preschool children. The in vitro model using Caco-2 cells showed that the uptake of β-carotene was significantly reduced (p < 0.05) in the presence of physiological amounts of ferrous chloride (30 μmol/L). There was further an inverse relationship (r2 = 0.93, p < 0.05) between the uptake of β-carotene and concentration of ferrous iron in the test solution provided to the Caco-2 cells. However, no effect of β-carotene on iron uptake was noticed.