EFFECT OF HEAT PROCESSING ON VITAMIN COMPOSITION OF SELECTED STAPLE GREEN LEAFY VEGETABLES IN NIGERIA

Abstract

This study assessed the effect of the steamed and boiling cooking methods on the vitamin content of six staple green vegetables in Nigeria. Vitamin levels in fresh, steamed and boiled leafy vegetables were determined using spectrophotometric and titrimetric methods. The results of vitamin analysis showed that fresh vegetable of Amaranthus hybridus contained the largest amount of ascorbic acid, thiamin and niacin (358.40 mg/100 g, 0.09 mg/100 g and 0.08 mg/100 g), while Talinum triangulare had the highest level of riboflavin (0.18 mg/100 g). The steamed Amaranthus hybridus contained the highest levels of ascorbic acid, thiamin and niacin (322.56 mg/100 g, 0.08 mg/100 g and 0.73 mg/100 g), while steamed leaves of Talinum triangulare had the highest quantity of riboflavin (0.16 mg/100 g). The boiled Amaranthus hybridus had the highest amount of ascorbic acid, thiamin and niacin (197.12 mg/100 g, 0.05 mg/100 g and 0.41 mg/100 g), whereas the boiled Talinum triangulare had the highest level of riboflavin (0.09 mg/100 g). The percentage of vitamin loss in steamed leafy vegetables varies from 9 to 11 %, 9 to 17 %, 9 to 13 % and 9 to 12 % in ascorbic acid, thiamin, riboflavin and niacin respectively. Almost 50 % of the essential vitamins were lost in boiled leafy vegetables. The results revealed that vegetables could be improved source of some important vitamins that can help humans meet their nutritional needs.