STUDY ON EFFECT OF TRADITIONAL PROCESSING METHODS ON NUTRITIONAL QUALITY AND SENSORY ACCEPTABILITY OF VALUE-ADDED PRODUCTS FROM COWPEA (Vigna unguiculata (L.) Walp.) GROWN IN ETHIOPIA

Abstract

Cowpea (Vigna unguiculata (L.) Walp.) is an important legume and an alternative source of protein which can be used as a substitute for animal protein that is limited in supply in Ethiopia. This study was initiated with the objective of determining the effect of different traditional processing methods on nutritional quality and sensory acceptability of two selected cowpea varieties (Bole and Kanketi) grown in Ethiopia. The experiments were carried out in a completely randomized design with cowpea varieties as the first factor of two levels (Bole and Kanketi) and processing methods as a second factor of the four levels (boiling, roasting, dehulled after roasting and fermentation). The results showed that the moisture content, crude protein, total ash, crude fiber, crude fat, utilizable carbohydrate and total energy of the raw cowpeas were 8.45%, 28.80%, 5.04%, 4.71%, 1.91%, 51.12%, 336.89 Kcal/100g and 8.91%, 25.32%, 4.71%, 6.60%, 2.12%, 52.34%, 329.72 Kcal/100g, for Bole and Kanketi varieties, respectively. After processing the values of these parameters were 8.00%, 27.44%, 4.81%, 3.61%, 1.75%, 54.39%, 343.03 Kcal/100g and 8.53%, 24.04%, 4.51%, 5.07%, 1.93%, 55.91%, 337.21 Kcal/100g, for Bole and Kanketi varieties, respectively. Fe, Zn and Ca, contents of raw cowpea variety were 15.65, 6.17 and 43.36 mg/100g, for Bole variety and 13.32, 4.99 and 41.91 mg/100g, respectively, for Kanketi variety. After processing, the contents were 13.46, 5.04 and 34.34 mg/100g for Bole variety whereas for Kanketi variety they were 11.65, 4.08 and 33.40 mg/100g, respectively. The anti-nutritional factors, tannin, and phytic acid were 28.43 and 80.37 mg/100g in the raw Bole variety while for Kanketi variety they were 31.23 and 127.99 mg/100g, respectively. After processing, these parameters were reduced to 16.75 and 50.37 mg/100g, respectively, for Bole whereas for Kanketi variety they were 18.42 and 80.05 mg/100g, respectively. The sensory acceptability scores of cowpea food products showed significant (p<0.05) differences for most of the quality parameters as affected by different processing methods. The products processed by boiling, roasting, dehulling after roasting and fermentation showed acceptability scores that ranged from 5.97 to 6.68 for appearance, 5.83 to 6.58 for color, 5.30 to 6.57 for flavor, 4.57 to 6.43 for taste, 5.12 to 6.55 for mouthfeel and 5.36 to 6.55 for overall acceptability in scale of 7 points. Functional properties, namely, bulk density, swelling power, solubility index, water absorption capacity and oil absorption capacity were 0.75 g/ml, 5.17%, 20.19%, 2.39 g/g, 2.24 g/g, respectively, for Bole variety while for Kanketi variety values were 0.79 g/ml, 5.22%, 17.56%, 2.54 g/g and 2.06 g/g, respectively. The cooking times of Bole and Kanketi varieties were 17.59 and 27.42 min, respectively. The result indicated that Boiling and dehulled after roasting processing methods were more effective in reducing anti-nutritional factors. Under different processing treatments, Bole cowpea variety exhibited low anti-nutritional concentrations. Hence, it can be used as a raw material in the food processing industries in the production of quality weaning and supplementary food products