Abstract
Bitter melon, Momordica charantia L, is a popular traditional medicinal fruit in tropical and subtropical countries. It has been linked with therapeutic effects, some of which are likely due to its flavonoids. To determine its total flavonoid content (TFC) and to prepare extracts for use as nutritional supplements or ingredients for nutraceutical functional foods, various solvents have been used, including water, which is the preferred solvent because it is inexpensive, safe and environmentally friendly. The study aimed to extract bitter melon, using five solvents (ethanol, methanol, n-butanol, acetone and water) before and after the optimal conditions for water were determined in terms of extraction temperature, time, ratio of water to bitter melon (mL/g) and number of times the same material was extracted. The TFC of six varieties of bitter melon was also determined. Acetone was the best of the five solvents for extracting flavonoids from the Moonlight variety (23.2 mg Rutin Equivalents (RE)/g). Even after increasing the extraction by 88% (1.24 vs 0.66 mg RE/g) using optimised conditions for the aqueous extraction (two extractions at 40℃ for 15 min at a ratio of 100:1 mL/g of bitter melon powder), the flavonoids extracted from the Moonlight variety using water was very little (5.4%) compared to acetone. Furthermore, using acetone, it was shown that the Moonlight variety (23.2 mg RE/g) bought at a local market had higher levels of flavonoids than the greenhouse-grown Jade (15.3 mg RE/g), Niddhi (16.9 mg RE/g), Indra (15.0 mg RE/ g), Hanuman (3.9 mg RE/g) and White (6.9 mg RE/g) varieties. Therefore, acetone was the best solvent for extracting flavonoids from bitter melon and the aqueous extraction could only be improved to extract 5.4% of the flavonoids extracted with acetone from the Moonlight variety, which had the highest TFC of the six varieties of bitter melon.
Highlights
Bitter melon, Momordica charantia L. is a member of the Cucurbitaceae family
Rutin was used as a standard and the total flavonoid content (TFC) was expressed as mg of Rutin Equivalents (RE) per g of bitter melon powder on a dry basis
Our findings were in agreement with a study by Ferreira & Pinho [23], which found that the flavonoid, hesperetin, was more soluble in acetone than in methanol, followed by ethanol, ethyl acetate and acetonitrile
Summary
Momordica charantia L. is a member of the Cucurbitaceae family. The latin name “Momordica” means ‘to bite’ and refers to the leaves of the bitter melon plants, which have jagged edges and look like they have been bitten [1]. Studies have reported that different varieties of bitter melon may differ in their content of bioactive compounds [9,10]. Ethanol [11,17], water [11] and methanol [18] have been used for extracting flavonoids and other bioactive compounds from bitter melon. Studies on the use of different solvents, including water and less polar organic solvents, for the extraction of flavonoids from different bitter melon varieties are still limited. If water is to be the solvent of choice, the optimal conditions for the aqueous extraction of flavonoids from bitter melon need to be determined. In the case of flavonoids, because they occur as aglycones and glycosides, the extraction efficiency obtained with optimal aqueous conditions needs to be compared with that of less polar solvents. The flavonoid content of six varieties of bitter melon was determined
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