Effects of cooking and storage on total-carotene, selected vitamins and minerals of selected Nigerian green leafy vegetables

Abstract

Changes in carotenes, selected vitamins and minerals of five locally consumed green leafy vegetables (Telfairia occidentalis, Amarranttus hybridus, Talinum triangulare, Pterocarpus mildbraedli and Gnetum africanum) upon cooking for 5 min at 100^oC of storage at room temperature (30^oC, 85% RH) for 5 days were determined. Fresh samples served as control. The total-carotene, vitamins (Vitamin C, Thiamin, Niacin, Riboflavin and Vitamin K₁ ) and minerals (Potassium, Calcium, Magnesium, Zinc and Iron) contents of the samples were analyzed using standard methods. Fresh T. occidentalis had significantly (p<0.05) highest total–carotene (953.78 µg/gdwt) while T. triangulare had the lowest (186.10 µg/gdwt). Apparent Retention of total-carotene after cooking were 184.10%, 123.70%, 524.45%, 171.87% and 110.66% in T. occidentalis, A. hybridus, T. triangulare, P. mildbraedli and G. africanum, respectively. The lowest to highest vitamins’ concentrations (mg per 100 g fwt) of the raw samples were significant (p<0.05): Vitamin C (P. mildbraedli, 20.06 to T. occidentalis, 160.15), Thiamin (T. occidentalis, 0.08 to G. africanum, 0.18), Niacin (P. mildbraedli, 1.55 to A. hybridus, 3.69), Riboflavin (P. mildbraedli, 0.46 to T. occidentalis, 2.07) and Vitamin K₁ (T. triangulare, 112.25 to A. hybridus, 122.21 µg/100g fwt). Cooking significantly (p<0.05) reduced the vitamins contents except vitamin K₁ . Mineral contents (mg/100g fwt) of fresh vegetables were Potassium (245 to 550), Calcium (80 to 150), Magnesium (95 to 430), Zinc (1.05 to 2.00) and Iron (2.50 to 10.40), respectively. Cooking significantly (p<0.05) decreased the mineral contents. Consumption of large quantities of the vegetables per serving could help meet the nutrients RDAs.