The effect of cooking methods on total phenolic and antioxidant activity of selected 'ulam'

Abstract

This study was conducted to determine the total phenolic content and antioxidant activity of selected green vegetables. The effect of thermal treatment on antioxidant activity and phenolic content were also studied. Brassica alboglabra (Kale), Amaranthus oleracea (spinach), Brassica rapa var parachinensis (flowering white cabbage) and Brassicajuncea (mustard green) were used in this study. Methanol was used as extracting solvent. The oxidative activity of methanol were measured by using 2,2- diphenyl-2- picrylhydrazyl (DPPH) assay method whereas, total phenolic compound (TPCs) was measured by using Folin-Ciocalteu method. Among the samples tested, methanol extracts of flowering white cabbage had a highest total phenolic content while the lowest was seen in spinach's extracts for the fresh ones. It is interesting to note that there were significant (p<0.05) difference between all samples tested. In Folin-Ciocalteu method, the samples of blanching method was seen to have the highest while boiling had the lowest in total phenolic content. In DPPH method, it is interesting to note that there were significant (p<0.05) difference towards the different cooking methods for the methanol extracts of kale. Among the samples tested, extracts of kale shown the highest antioxidant activity during all cooking methods except for blanching method. There were no significant difference in oxidative activity towards all different cooking method in extracts of spinach and mustard green. In DPPH method, the fresh samples showed the highest while boiling method was seen to have the lowest in antioxidant activity.