Polyphenol and flavonoid contents, antioxidant activities and glycaemic index of Dioscorea spp and Coleus esculentus from Cameroon

Abstract

The World Health Organization (WHO) encourages the use of local natural resources for the maintenance of human health. However, some tubers with interesting nutritional properties are rarely found in the diet of the Cameroonian population. This study aims at investigating the flavonoid and polyphenol contents, antioxidant activities, and glycaemic index of four varieties of yam tubers, namely: Dioscorea schimperiana, Dioscorea bulbifera, Dioscorea burkilliana and Coleus esculentus. Standard methods were used to determine the total flavonoid and polyphenol contents, DPPH and FRAP antioxidant activities, and glycaemic index. Total flavonoids ranged from 77.49 to 11,327.52 mg CE/100 g DM (dry matter) and phenolic compounds from 50.95 to 3664.26 mg GAE/100 g DM, FRAP-reducing capacity of tubers varied between 137.61 and 14,879.62 mg FeSO4/100 g DM. DPPH-scavenging activities ranged from 0.85 to 40.65 mg GAE/ml. A correlation was observed between phenolic compounds and FRAP-reducing activity (R2=0.999, p<0.001) and between flavonoids and FRAP-reducing capacity (R2=0.951, p<0.001). C. esculentus presented a low glycaemic index; D. burkiliana and D. shimperiana had medium glycaemic indices; and D. bulbifera showed a high glycaemic index. Thus, red D. shimperiana (West) could be used as a natural antioxidant while C. esculentus (NW) could be used in the management of chronic diseases, especially diabetes.