An Optimised Aqueous Extract of Phenolic Compounds from Bitter Melon with High Antioxidant Capacity

Sing Tan,Costas Stathopoulos,Sophie Parks,Paul Roach

doi:10.3390/antiox3040814

Abstract

Bitter melon (Momordica charantia L.) is a tropical fruit claimed to have medicinal properties associated with its content of phenolic compounds (TPC). The aim of the study was to compare water with several organic solvents (acetone, butanol, methanol and 80% ethanol) for its efficiency at extracting the TPC from freeze-dried bitter melon powder. The TPC of the extracts was measured using the Folin-Ciocalteu reagent and their antioxidant capacity (AC) was evaluated using three assays. Before optimisation, the TPC and AC of the aqueous extract were 63% and 20% lower, respectively, than for the best organic solvent, 80% ethanol. However, after optimising for temperature (80 °C), time (5 min), water-to-powder ratio (40:1 mL/g), particle size (1 mm) and the number of extractions of the same sample (1×), the TPC and the AC of the aqueous extract were equal or higher than for 80% ethanol. Furthermore, less solvent (40 mL water/g) and less time (5 min) were needed than was used for the 80% ethanol extract (100 mL/g for 1 h). Therefore, this study provides evidence to recommend the use of water as the solvent of choice for the extraction of the phenolic compounds and their associated antioxidant activities from bitter melon.

Highlights

Bitter melon (Momordica charantia L.) is a popular medicinal fruit in Asia and Africa, where many varieties are grown
This study demonstrated that the aqueous extraction of phenolic compounds from bitter melon was as efficient as organic solvent extractions, when the extraction conditions were optimised
This study demonstrated that water could be used to effectively extract phenolic compounds and their associated antioxidant activities from bitter melon

Summary

Introduction

Bitter melon (Momordica charantia L.) is a popular medicinal fruit in Asia and Africa, where many varieties are grown. Owing to the hydroxyl groups, most phenolics in bitter melon are hydrophilic compounds, such as gallic acid, gentisic acid, catehcin, chlorogenic acid, epicatechin, vanillin acid, protocatechuic acid, p-coumaric acid, o-coumaric acid, and t-cinnamic acid [9,10]. Studies have reported that phenolics have potent antioxidant and free radical-scavenging activities [11,12]. Whole bitter melon (flesh, aril and seeds) has been shown to be a good source of phenolic compounds [9] and one study demonstrated that the flesh, aril and seeds all had very high antioxidant activity [9]. Another study suggested that the antioxidant and free radical scavenging properties in the extracts of bitter melon could be attributed to flavonoids and other phenolic compounds [11]. The results revealed that, on a weight per weight basis, the bitter melon had better 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) than vitamin E [11]

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