Total phenolic contents and phenolic acid constituents in 4 varieties of bitter melons (Momordica charantia) and antioxidant activities of their extracts

Four varieties of bitter melon (Momordica charantia), India green (IG), India white (IW), China green (CG), and China white (CW) were analyzed for total phenolics, phenolic acid constituents, and antioxidant activities of their methanolic extracts. Phenolic contents of the oven-dried and freeze-dried tissues ranged from 5.39 to 8.94 and 4.64 to 8.90 mg chlorogenic acid equivalent (CAE)/g on dry weight basis, respectively. Phenolic contents of bitter melon seed, inner tissues, and flesh ranged from 4.67 to 8.02, 4.64 to 8.94, and 5.36 to 8.90 mg CAE/g, respectively. The total phenolic contents of IG, IW, CG, and CW were 4.64 to 6.84, 6.03 to 8.94, 5.39 to 7.81, and 6.07 to 8.90 mg CAE/g, respectively. The main phenolic acids in flesh were gallic acid, gentisic acid, catechin, chlorogenic acid, and epicatechin, which ranged from 8.04 to 39.76, 16.99 to 32.39, 23.06 to 82.45, 4.55 to 15.83, and 16.14 to 44.28 mg/100 g on dry weight basis, respectively, while in inner tissues were gallic acid, gentisic acid, catechin, and epicatechin, which ranged from 2.57 to 18.05, 5.39 to 32.61, 13.54 to 39.74, and 2.96 to 40.91 mg/100 g, respectively. The main phenolic acids contained in seeds were gallic acid, catechin, and epicatechin, which ranged from 4.61 to 18.9, 13.2 to 57.61, and 6.00 to 40.08 mg/100 g, respectively. There was no significant difference in the antioxidant activities of the extracts among varieties (P = 0.2556) and between drying methods (P = 0.1444). The antioxidant activities of flesh, inner tissue, and seed ranged from 81.7% to 86.5%, 78.8% to 88.4%, and 78.5% to 85.4% inhibition, respectively. Bitter melon is a rich source of phenolic compounds. These natural plant phenolics can be a good source of antioxidants for application in food system.