Antioxidant property and α-glucosidase, α-amylase and lipase inhibiting activities of Flacourtia inermis fruits: characterization of malic acid as an inhibitor of the enzymes

Abstract

Flacourtia inermis Roxb. (Flacourtiaceae), is a moderate sized tree cultivated in Sri Lanka for its fruits known as Lovi. The current study was undertaken to study the biological activity of extracts of the fruits in an attempt to increase the value of the under exploited fruit crops. Fruits of F. inermis were found to be rich in phenolics and anthocyanins. Polyphenol content of the fruits was determined to be 1.28 g gallic acid equivalents per 100 g of fresh fruit and anthocyanin content was estimated as 108 mg cyanidin-3-glucoside equivalents per 100 g of fresh fruits. The EtOAc extract showed moderate antioxidant activity in the DPPH radical scavenging assay with IC50 value of 66.2 ppm. The EtOAc and MeOH extracts of the fruits also exhibited inhibitory activities toward α-glucosidase, α-amylase and lipase enzymes with IC50values ranging from 549 to 710 ppm, 1021 to 1949 ppm and 1290 to 2096 ppm, respectively. The active principle for the enzyme inhibition was isolated through activity-guided fractionation and was characterized as (S)-malic acid. The results of this study indicate that F. inermis fruits have the potential to be used in health foods and in nutritional supplements.