Ascorbic acid changes in three indigenous Kenyan leafy vegetables during traditional cooking

Abstract

The ascorbic acid (vitamin C) contents in three fresh green leafy vegetables commonly consumed in Kenya namely, Amaranthus hybridus, Gynandropsis gynandra and Solanum nigrum L. and the changes during traditional cooking were measured. In the fresh leaves, the ascorbic acid varied from 123.8 mg/100 g fresh weight in A. hybridus to 189.2 mg/100 g fresh weight in G. gynandra. Cooking for 20 min in boiling water led to losses of between 75 and 89%. Smaller losses in ascorbic acid were observed when the leafy vegetables were cooked in two and four volumes of water. The loss in ascorbic acid as a function of cooking time was highest in S. nigrum while its loss as a function of volume of cooking water was highest in A. hybridus. Using loss in ascorbic acid as an index, it is proposed that controlling the time and amount of water used in cooking without sacrificing palatability could help, at least in part, in preventing loss in other essential nutrients during traditional cooking of the vegetables.