The study examined the chemical composition of fresh, sundried tender leaves and husks of cowpea ‘Adengee’ (Vigna unguiculata) and organoleptic attributes of their traditional soups. Information on processing, preparation and utilization of soup meals based on cowpea leaves and husks were obtained during the focus group discussion. The tender leaves and husks were parboiled and sundried. Proximate, micronutrients, phytochemicals and antinutrient levels were determined using standard procedures. The soups based on fresh and sundried leaves and husks were analysed prior to sensory evaluation. The data collected were statistically analysed using means, standard deviation and standard error. All values were based on residual moisture. Protein for dried leaves was higher (p<0.05) (39.24 vs. 21.98 and 13.95%) than those of fresh leaves and dried husks. Dried leaves and husks had lower fat than the control (1.31 and 0.75 vs. 9.10%) (p<0.05). Sun drying increased ash in both dried leaves and husks (14.74 and 10.86 vs. 4.82%). The lower value for fibre in the dry samples was rather surprising (14.20 and 20.42 vs.25.13%) (p<0.05). Carbohydrate significantly increased more in dried husks than in dried leaves. (53.76 Vs. 30.22%) (p<0.05).The micronutrients in both dried leaves and husks were reduced due to their volatile nature. Tannins, saponins, flavonoids and polyphenols decreased significantly (p<0.05) in processed samples due to drying. Soups based on dried leaves (DS) had higher protein (p<0.05) relative to the soup based on dried husks (HS) and fresh leaves (FS) (34.40 vs.34.10 and 33.30%). Similarly, husks based soups had higher fat (34.10 vs.34.05 and 31.44%)(p<0.05) Ash was higher in dried leaves based soup(7.83%) and fresh leaves soup (7.20%). Fibre for the husks based soup was higher (p<0.05) relative to fresh and dried leaves based soups (6.13 vs.5.58 and 6.11%, respectively). The carbohydrate levels were generally appreciable. All soups had appreciable levels of calcium, phosphorus and iron. These minerals varied significantly amongst the soups (p<0.05). Zinc and iodine also differed (p<0.05).β-carotene content of soup based on fresh leaves was higher (p<0.05) relative to those based on dried leaves and husks (6.08 vs.5.07 and 5.46RE).Vitamin C varied significantly (0.90 to 1.10mg) in soups based on fresh leaves and dried husks. Tannins, saponins, polyphenols and flavonoids in soups based on fresh leaves and dried husks were comparable. Anti nutrients levels in all soups were generally low. Scores for all organoleptic attributes of the three soups were more than half (6.17 to 7.70) of the 9-point scale. The soups were generally acceptable. As judged by the results, cowpea leaves, husks and their soups have high nutrient potentials to justify its cultivation, consumption promotion and diversification. Consumption related information such as nutritional properties should be packaged and extensively promoted to broaden the knowledge of health and nutritional benefits of consuming cowpea leaves and husks. The results demonstrate that, there is a potential in developing multi-purpose varieties with good performance, which are well-yielding in both leaves and seeds. Therefore, production related information, such as variety, yields and cultivation practices as well as processing should be packaged and made available to extension personnel and governmental agricultural research institutes that often have a good outreach to farmers.
1.1 Background to the study
The scarcity of documented information on the nutrient potentials of most of the foods consumed in Nigeria has greatly contributed towards the ineffectiveness of nutrition education programmes to meet the nutrient needs of a vast segment of the Nigerian population. This lack of documented nutrition information has precipitated wrong choices of foods, low nutrients intake and delay in embracing food diversification. The knowledge of the influence of processing on the chemical composition of foods is also necessary for optimizing nutrient reiteration during handling and processing of our local food materials (Ibok,Ellis & Owusu,2008).
Recently, researchers have become convinced that nutrients found in fruits and vegetables do more than just prevent diseases such as beriberi or rickets. The most publicized finding reveals that certain vitamins or vitamin precursors, notably vitamin C; beta-carotene as well as polyphenols are powerful antioxidants (Consumer Report on Health, 1998). Antioxidants prevent molecular damage caused by oxidation in that, the protection offered may fend off many diseases and muscular degeneration (Islam et al., 2002).
Cowpea (Vigna unguiculata L. Walp), an annual herbaceous legume originated in Africa and is wildly grown. Drought tolerance; short growing period and its multi-purpose use make cowpea a very attractive crop to farmers who cultivate in marginal, drought-prone areas with low rainfall and less developed irrigation systems where infrastructure, food security and diminishing malnutrition are major challenges (Hallensleben, Polrech, Heller &, Maass, 2009). Lawrence and Whitbread (2006) described cowpea as one of the most important tropical dual-purpose legumes, being used as leafy vegetable, grain, as fresh cut-and-carry foliage, and for hay and silage.
Cowpea has much variability within the species. The specie under study is local specie with coiled pods (Adengee in Tiv,). The fresh seeds are greenish but golden brown when dried and relatively small in size compared with the common black eyed beans. This crop can be used at all stages of growth as a vegetable crop. The tender green leaves are an important food source in Tiv communities in Benue State. The green leaves serve as an ingredient in egusi (melon) soup just like spinach is used in egusi soup; or the leaves are blanched and sun dried for with egusi soups all year round. The immature pods are boiled, the boiled seeds are eaten as vegetable and the husks are sun dried, prepared as egusi soup.