Bitter gourd (Momordica charantia L.) has long been regarded as a food and medicinal plant. We investigated
the antioxidant activity of the water extract of leaf, stem and fruit fractions by several in vitro
systems of assay, namely DPPH radical-scavenging activity, hydroxyl radical-scavenging activity,
b-carotene–linoleate bleaching assay, ferric reducing/antioxidant power (FRAP) assay and total antioxidant
capacity. Total phenolic content was measured by Folin–Ciocalteu reagent. Identification of phenolic
compounds was achieved using HPLC with the UV-diode array detection. The extracts of different fractions
were found to have different levels of antioxidant activity in the systems tested. The leaf extract
showed the highest value of antioxidant activity, based on DPPH radical-scavenging activity and ferric
reducing power, while the green fruit extract showed the highest value of antioxidant activity, based
on hydroxyl radical-scavenging activity, b-carotene–linoleate bleaching assay and total antioxidant
capacity. The predominant phenolic compounds were gallic acid, followed by caffeic acid and catechin.
The present study demonstrated that the water extract fractions of bitter gourd have different responses
with different antioxidant methods. Total phenol content was shown to provide the highest association
with FRAP assay in this present study (R2 = 0.948).