Effect of traditional open sun-drying and solar cabinet drying on carotene content and vitamin A activity of green leafy vegetables

Dried green leafy vegetables constitute a major dietary source of provitamin A carotenoids for people living in semi-arid areas of Tanzania. In the present study, eight vegetable varieties commonly consumed in these areas were either traditionally sun-dried or solar-dried, and the amount of provitamin A carotenoids were determined by HPLC. In the fresh blanched leaves, the contents of β-carotene, α-carotene, 9-cis-β-carotene and 13-cis-β-carotene were in the range of 526–917, 12–39, 80–136 and 16–40 μg/g dry matter/basis; dmb, respectively. The average amounts of all-trans-β-carotene in the leaves after blanching, solar drying and open sun-drying were 662, 502 and 353 μg/g dmb, respectively, all significantly different from each other (p <0.001). The average amounts of all-trans-α-carotene were 21, 15 and 8 μg/g dmb (p <0.05) and of 9-cis-β-carotene 101, 82 and 63 μg/g dmb (p <0.05) in the blanched, solar-dried and open sun-dried samples, respectively. Estimation of the amount of retinol equivalents provided by the dried vegetables for preparation of an edible portion of 100 g relish showed that solar-dried vegetables contributed more (between 120–275%) than the recommended level of vitamin A, and on average 43% more retinol equivalents than relishes of open sun-dried vegetables.