Antioxidant and α-Glucosidase Inhibitory Activities of Cucurbit Fruit Vegetables and Identification of Active and Major Constituents from Phenolic-rich Extracts of Lagenaria siceraria and Sechium edule

Antioxidant and alpha-glucosidase activities and total phenolic contents (TPC) in sequential extracts of dried pulps from seven cucurbit fruit vegetables were determined for the first time. The highest TPC and metal chelating activity were obtained from the chloroform extracts of Luffa acutangula (28.04 +/- 0.37 mg GAE/g extract) and Benincasa hispida (EC50 = 0.44 +/- 0.03 mg/mL), respectively. The ethyl acetate extract of Sechium edule showed the highest 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity (951.73 +/- 29.14 mM TE/g extract). The highest reducing and anti-alpha-glucosidase activities were shown by the methanol and ethyl acetate extracts of Momordica charantia (692.56 +/- 43.38 mM AscAE/g extract; 66.64 +/- 2.94%, respectively). The highest correlation (r = 0.99) was observed between the TPC and DPPH values of S. edule. Although caffeic acid was quantified as the major constituent in the methanol extract of Lagenaria siceraria, isoquercetin was found to be the main contributor to the activities. Gallic acid was identified as both the main and most active antioxidant constituent in the ethyl acetate extract of S. edule.