|
|
 |
 |
| |
 Printable version |
Provitamin A content of traditional green leaves from Niger |
Cahiers Agricultures. Volume 6, Number 6, 553, Décembre 1997, Etudes originales
|
 Résumé
|
Author(s) : Hélène Delisle, Seidou Bakari, Guylaine Gevry, Chantal Picard, Guylaine Ferland |
Summary : As part of a study on vitamin A intake of preschool children in Niger, traditional green leaves as locally processed were sampled for provitamin A determination, using HPLC (high performance liquid chromatography). A total of 168 samples from 15 plant species were collected from three different villages in western Niger, two in Bouza district and one in Ouallam district.
The main species available and consumed throughout the year, supply sources, and processing methods, were identified in a preliminary study. In both districts, most women are involved in drying leaves. Dried greens are used year-round, mostly in soups served with the staple dish of millet, while fresh leaves are mainly prepared during the rainy season, either boiled or steamed with millet flour. Plant species found in both areas are usually processed similarly, but not all species were found in a given site. Samples of processed leaves were collected during the rainy season. In a given village, three different women provided a sample of every leaf species available for every processing method used. Weighed specimens of dried or fresh cooked leaves were wrapped in opaque plastic bags, quickly frozen, and shipped to Montreal on dry ice for analysis. Provitamin A carotenoid determinations were done in duplicate with the results expressed as total provitamin A carotenoid ( g of retinol equivalents RE) per 100 g. Moisture content was also determined for all samples after drying in a conventional oven for 48 to 72 h.
The average provitamin A level for the 57 samples of dried leaves was 2,273 ± 1,152 RE/100 g, ranging from a low of 861 in Adansonia digitata to a high of 3,681 in Ceratoteca sesamoides (Table 1). The variance was very high and significant differences were observed among plant species and collection sites. Residual moisture did not vary according to species and site, and therefore could not explain the observed differences. Fresh boiled leaves had on average 1,333 ± 596 RE/100 g fresh weight, and steamed leaves 928 ± 526 RE (Table 2). For fresh leaves, in addition to species and site, the cooking method was significantly associated with the provitamin A level. For the four species cooked either way (Figure 1), boiled leaves had a higher provitamin A content than steamed leaves, both on a fresh and dry weight basis; this difference could not be ascribed to cooking time. Per dry weight unit (Table 3), leaves collected in the dried state had roughly half the provitamin A content of samples cooked fresh, and steamed leaves had half as much provitamin A as boiled samples of the same species. After adjustment for the processing method, species with the highest level of provitamin A, on a dry weight basis, were Allium cepa (onion greens), C. sesamoides (false benniseed) and Hibiscus sabdarifa (red sorrel).
Despite wide variations in the provitamin A content of green leaves, these food items can be major contributors of vitamin A for children in the study areas. Depending on the species and type of dish, a small portion could provide from 11% to 104% of the safe vitamin A intake level for young children (Table 4). The study suggests that in rapid dietary assessments, fresh boiled greens should be distinguished from other green leaf dishes, in view of their provitamin A content. Based on children’s food intake data, the estimated contribution of green leaves was on average two-thirds of the safe vitamin A intake level, but with a wide range. The real contribution of green leaves to vitamin A requirements may however be much lower, as the bioavailability of green leaf carotenoids is likely much lower than was assumed until recently, and as requirements may be increased in these children as a result of high exposure to infection. Elucidation of the above issues is needed for relevant food-based strategies to be advocated for the prevention of vitamin A deficiency in tropical Africa. |
Keywords : |
|
