Seasonal variation of phenolics, flavonoids, antioxidant and lipid peroxidation inhibitory activity of methanolic extract of Melilotus indicus and its sub-fractions in different solvents

Abstract

In the present work, seasonal variations of total phenolic and flavonoid contents, antioxidant activity and lipid peroxidation inhibitory activities of methanolic extract of Melilotus indicus and its sub-fractions in different solvents have been evaluated. The study was conducted on plant samples collected in February and April which are its flowering and fruiting seasons respectively. Both phenolic and flavonoid contents were higher in methanolic extract of the plant collected in April than in February. Free radical scavenging activity measured through DPPH method was low in methanolic extracts of both the samples, although it decreased as we go from February to April. Ethyl acetate fractions showed highest % inhibition. Total antioxidant activity of methanolic extracts measured through phosphomolybdate assay remained almost same. Chloroform fraction showed the highest value in both the seasons with value in April higher than in February, 57.24 and 46.44 µg of ascorbic acid equivalents per mg of the dried mass, respectively.  The methanolic extract of April sample showed higher FRAP (ferric reducing antioxidant power) value than that of February. In February, ethyl acetate fraction showed highest FRAP value, while in April, chloroform exhibited the highest value. Methanolic extracts and fractions in all solvents showed remarkable ability to inhibit peroxidation in linoleic acid. After 72 hours, all samples were much more effective than the standard BHA. Seasonal variations affect biosynthesis of different types of antioxidant and free radical scavenging compounds in Melilotus indicus. Thus, the medicinal and nutritional value of the plant will depend on harvesting season