Protein and Iron composition of cowpea leaves: An evaluation of six cowpea varieties grown in eastern Africa
Mineral element, protein-energy and micronutrient deficiencies are primary public health concerns in Eastern and Southern Africa. Promoting the consumption of traditional vegetables such as leaves of cowpea Vigna unguiculata (L.) Walp could provide cheap sources of protein, micronutrients and mineral elements that can improve the nutritional status of resource-poor subsistence farmers. This study evaluated leaves of two Ugandan cowpea landraces (Icirikukwai and Ebelat) in comparison to four Tanzanian varieties (UG-CP-9, Dakawa, Ex-Iseke and IT 93K-2045-29) for leaf crude protein and iron contents. Tender vegetable leaves of landraces, four cowpea varieties and all possible 2-way, 3-way and 4-way combinations were harvested from three trial sites in the villages of Serere, Kikota and Kogili in eastern Uganda. Near Infrared Spectrometry (NIRS) was used to determine the crude protein content and iron concentration of open-air dried leaf samples. ANOVA for the leaf crude protein content and iron concentration data was done using the GLM procedure of SYSTAT. Leaf crude protein of Icirikukwai and Ebelat was 33.0 and 31.3%, while iron concentration was 332.8 and 379.4 µg/g, respectively. Leaf crude protein for the individual varieties was highest (31.84 %) in UG-CP-9 leaves and lowest (28.02%) in Ex-Iseke variety. Leaf crude protein for 2-way, 3-way and 4-way mixtures was 30.99, 29.98 and 30.32%, respectively. Leaves from Dakawa variety had the highest iron concentration (349.1 µg/g) of the four Tanzanian varieties tested. The mixture involving leaves from all the four varieties had the highest iron concentration values of 266.1 µg/g while 2-way mixtures gave the lowest iron concentration of 253.2 µg/g. Compared to the tested varieties and their mixtures, iron concentration of landraces was not significantly higher. The protein content varied significantly across all the treatments and sites and was relatively high for a plant source. In addition, cowpea leaves are available as food throughout the cropping season and, thus, can be used for improved food security. These benefits, thereby, make cowpea leaves an indispensable tool to improve the nutritional status of resource-poor subsistence farmers in countries where cowpea is grown.
Key words: Vigna unguiculata, nutritional quality, leafy vegetables