Selection and optimisation of extraction technique for the preparation of phenolic- and flavonoid-rich extract of leafy vegetable, Coccinia grandis (Linn.) Voigt

Abstract

Coccinia grandis (L.) Voigt (family: Cucurbitaceae) is a popular leafy vegetable in Sri Lankan diet. C. grandis is high in phenolics and flavonoids. The present work attempted to determine a suitable extraction technique, and further optimise it to obtain phenolic- and flavonoid-rich extract from C. grandis leaves, with an aim at developing a nutraceutical targeting the dietary management of diabetes mellitus. Acetone extraction (AE), methanol extraction (ME), pre-warmed water extraction (PWE), electric shake extraction (ESE), reflux extraction (RE), ultrasonication with water (UEw), ultrasonication with ethanol (UEe), ultrasonic assisted-reflux extraction (URE), and reflux assisted-ultrasonic extraction (RUE) were chosen as the extraction techniques. URE was selected as a satisfactory extraction technique for further optimisation for the preparation of phenolic- and flavonoid-rich extract based on the contents of phenolics (32.97 ± 0.41 mg of equivalent gallic acid/g of extract) and flavonoids (4.50 ± 0.04 mg equivalent quercetin/g of extract). The highest yield of 32.8% was obtained by the URE technique. The optimal extraction conditions for URE were determined with an ultrasonic time of 19 min, refluxing time of 168 min, and liquid:solid ratio of 16.4 mL/g. This is the first attempt to investigate the selection and optimisation of an extraction technique for obtaining phenolic- and flavonoid-rich extract from C. grandis leaves. The present findings would be useful in the development of a commercially viable nutraceutical using a phenolic- and flavonoid-rich extract of C. grandis.