Effect of Different Cooking Methods on the Concentration of Vitamin C in Cowpea Vegetable (Vigna unguiculata)

Background: Vitamin C is a water-soluble vitamin widely distributed in nature, mostly rich in fresh fruits and green leafy vegetables. The amount of Vitamin C in a given food depends on soil condition, climate in their area of growth, storage condition after harvest, and methods of preparation. Much amount of Vitamin C in vegetables is lost during cooking and there are still limited information on the impact of different cooking methods on the vitamin C content in leafy vegetable like cowpea vegetable (Vigna unguiculata). It is upon this background that this study aimed to determine the concentration of Vitamin C in cowpea vegetable when cooked using different cooking methods.

Methodology: Vitamin C concentration in a solution of cowpea vegetable cooked by different cooking methods (boiling, steaming and microwave methods) was determined by a redox titration using iodine in the presence of starch indicator. This was conducted at Busitema University, Faculty of Science and Education, Biology Laboratory in Uganda.

Results: The study revealed that cooking cowpea vegetable using microwave yields the highest concentration of vitamin C (154.8 mg/L), followed by steaming (142.9 mg/L) and boiling yielding the least concentration of vitamin C (130.4 mg/L).

Conclusion: The concentration of vitamin C obtained by the three methods of cooking cowpea vegetable has shown that microwaving method of cooking yields the highest concentration of vitamin C followed by steaming method and finally boiling. Further studies should be done to explain the variation of vitamin C concentration in cowpea vegetable when cooked using the above cooking methods. Similar studies should be conducted on other leafy vegetables which are potential sources of Vitamin C.