Analysis of the Effect of Cooking Duration on Nutrient Retention in Cowpea Prepared in Iron Pots in Niger State

Traditional cooking practices in Niger State, North Central Nigeria, involve prolonged boiling of cowpeas in unlined iron cooking pots, which may influence both nutrient retention and iron leaching into food. This study analyses the effect of cooking duration on the retention of protein, iron, zinc, vitamins B1 and B2, and antinutritional factors including tannins and phytate in cowpeas cooked in iron pots for 30, 60, and 90 minutes. Dried cowpea samples of the Ife Brown variety obtained from Minna markets were prepared using standard household cooking procedures. Cooked samples were freeze-dried, ground, and analysed by standard AOAC methods for proximate composition, mineral content by atomic absorption spectrophotometry, vitamins by HPLC, and antinutritional factors by colorimetric methods. Iron concentration in cooked cowpeas increased by 31.7% at 90 minutes compared to raw samples, attributed to iron leaching from the pot surface at low pH generated during cooking. Protein retention declined progressively from 94.3% at 30 minutes to 86.1% at 90 minutes. Thiamine showed the greatest heat sensitivity, with 42% loss at 90 minutes. Phytate and tannin reductions were highest at 60 minutes, improving mineral bioavailability. The findings recommend optimised cooking times of 60 minutes in iron pot preparation of cowpeas in North Central Nigerian dietary contexts. Keywords: cowpea, cooking duration, nutrient retention, iron leaching, Niger State