STUDY OF COOKING PARAMETERS ON THE DEGRADATION OF ASCORBIC ACID CONTAINED IN GREEN LEAFY VEGETABLES PRODUCED AND CONSUMED IN THE KARA REGION-TOGO

The purpose of this study is to quantify the content and investigate the effects of cooking temperature and time on the variability of vitamin C content in six green leafy vegetables: Solanum macrocarpon, Hibiscus sabdarifa, Octimum gratissimum, Vernonia amygdalina, Adansonia digitata and Corchorus olitotius. Two methods were used to determine the vitamin C contents of the samples processed by blanching and boiling at different cooking times. With the iodometric method, Hibiscus sabdarifa (0.5368 mg/g) and Adansonia digitata (0.5016mg/g) have the highest vitamin C contents, while Octimum gratissimum has the lowest concentration of 0.1760 mg/g. The results of quantification obtained by the spectrophotometric method present practically the same results as those of the iodometric method with as light decrease of 0.0242 mg/g for Hibiscus sabdarifa and an increase of 0.0147 mg/g for Adansonia digitata. The results of the study of the effect of temperature and cooking time, whatever the method, showed with the blanching, a loss of rate of 30,21% in vitamin C for Hibiscus sabdarifa and Solanum macrocarpon a loss of rate of 4,25%. The degradations were more considerable during the boiling of 15 min with maximum losses in the order of 79,05% for the leaves of baobab boiled and 45,24% respectively for Adansonia digitata and Solanum macrocarpon.