Cooking enhances the antioxidant properties of some tropical green leafy vegetables
Most leafy vegetables undergo cooking before consumption in tropical Africa. Therefore, this study sought to evaluate the effect of cooking on the vitamin C, total phenolics, total flavonoid and antioxidant properties [1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical and 2,2- azinobis -3-
ethylbenzo-thiazoline- 6-sulfonate radical (ABTS*) scavenging abilities, reducing property and Fe2+ chelating ability] of some tropical green leafy vegetables; Talinium triangulare, Ocimum gratissimum, Amaranthus hybridus, Telfairia occidentalis, Ipomea batata, Cnidoscolous aconitifolius, Baselia alba and Senecio biafrae leaves. The results of the study revealed that cooking causes a significant (P <0.05) decrease in the vitamin C [raw (321.4 - 842.0), cooked (198.2 - 638.4 mg/100 g)] content. Conversely, there was a significant (P < 0.05) increase in the total phenol [raw (146.9 - 693.8), cooked (272.9 - 1037.5 mg/100 g)] , total flavonoid [raw (8.2 - 53.0), cooked (12.9 - 57.4 mg/100 g)], DPPH radical scavenging ability [raw (15.7 - 61.8), cooked (52.8 - 92.7 %)], reducing property [raw (28.3 - 61.8), cooked (43.9 – 71.6 mg/100g AAE)], Fe2+ chelating ability [raw (17.4 – 75.4), cooked (22.8 - 89.2%)] and ABTS* scavenging ability [raw (17.4 - 87.3), cooked (57.5 - 113.2 mmol/100 gTEAC)]. In view of this, it could be concluded that cooking decreases the vitamin C contents in all the vegetables, while it increased the phenolic content and antioxidant activities.
Key words: Vegetables, cooking, antioxidant, phenolic, vitamin C.