ABSTRACT

Nutritional loss during food processing has become a major concern in recent times especially major essential mineral nutrients. There is need to know the appropriate cooking time for green leafy vegetables since they provide essential minerals in the diet of man. Hence, the cooking effect on commonly consumed green leafy vegetables in Lagos State was undertaken ascertain the level of mineral reduction with cooking time. Green leafy vegetables were collected from Lagos Polytechnic farm and subjected to cooking for 5, 10, 15 and 30 min. Potassium, sodium, magnesium, calcium, phosphorus and iron contents were evaluated in the treated vegetables using an Atomic Absorption Spectrometer. The study showed Jute mallow to be rich in potassium (38.43±0.06 mg/g), sodium (173.44±0.01 mg/g) and phosphorus (174.64±0.00 mg/g); Water leaf contained magnesium (38.43±0.06 mg/g) and calcium (74.88±0.02 mg/g), while bitter leaf was a good source of iron (18.85±0.01 mg/g). Both Lagos and African spinach had the lowest mineral contents when compared to the other vegetables. However, there was a significant reduction (p<0.05) in mineral contents with cooking duration, with water leaf having the highest percentage mineral depletion (>40%) after 5 min of cooking. Moderate mineral reduction was observed in both bitter leaf and jute mallow. Fluted pumpkin, Lagos and African spinach showed minimal mineral reduction in the study. Cooking for not more than 5 min for water leaf, and for <15 min for both bitter leaf and jute mallow was considered best for retention of ~50% of the original mineral contents, while fluted pumpkin, and Lagos and African spinach still retained more than 50% of their initial mineral contents even after 30 min of cooking.