Abstract:
Consumption of vegetables is the most sustainable way of reducing and controlling
micronutrient deficiencies in resource-poor communities. However, not much has
been documented about standard recipes that are of high nutritional quality in terms
of minerals and vitamins. The aim of this study was to modify traditional cowpea
leaf vegetable preparation methods to enhance carotenoid retention and iron
bioavailability. Modification principles included reducing cooking time, addition of
yoghurt, addition of oil and use of oven drying. Other objectives were to measure
nutrient composition of two varieties of cowpea leaf (Dakawa and Ex-Iseke) found in
rural Tanzania and to compare carotenoid retention and iron bioavailability of
cowpea leaves with those of selected leafy vegetables (cowpea, pumpkin, amaranth,
kangkong and sweet potato). Carotenoids were analyzed using High Performance
Liquid Chromatography and iron bioavailability by in vitro method. The two cowpea
leaf varieties were found to be good sources of carotenoids 44.43±0.03mg (Dakawa)
and 41.54±0.01mg (Ex-Iseke), vitamin C 86±0.02mg and 94±0.00mg, calcium
165±0.03mg and 142±0.01mg, phenols 575±0.02mg and 558±0.01mg, flavonoids
604.47±0.03mg and 723.36±0.02mg per 100g edible portion and antioxidants
2596±0.01μmoleTE and 2416±0.01μmoleTE respectively. However, very high
amounts of anti-nutrient oxalate 418±0.00mg and 348±0.03mg were observed.
Traditional cowpea leaf dish cooked with oil, onion, tomatoes and coconut milk for
30 minutes had significantly (P<0.05) the highest beta-carotene (40.83%±7.00) and
lutein (34.60%±3.30) retention compared to other traditional recipes. The highest
iron bioavailability (10.04%±0.49) was observed in traditional recipe which involved
boiling fresh cowpea leaves for 15 minutes. Modifying traditional preparation
methods did not significantly improve carotenoid retention and iron bioavailability
(p>0.05). All selected vegetables had promising carotenoid retention with lutein and
beta-carotene having more than 50% retention. Iron bioavailability increased with
cooking except for sweet potato leaves. Based on the results, it is concluded that not
all principles used for modifying traditional vegetable recipes for enhanced
carotenoid retention and iron bioavailability works for every vegetable.
