Phytochemical Screening and Quantitative Determination of Antioxidant Properties of Watermelon Rinds and Seeds

Abstract

In this present age of food insecurity, it is essential to source for agricultural waste that can be nutritionally beneficial to humans and animals. Watermelon rinds and seeds are regarded as agricultural wastes which need to be utilized for human and animal nutrition. This research work is aimed at examining the extractive values, qualitative and quantitative determination of phytochemicals and antioxidants properties in watermelon rinds and seeds and their solvent extracts using six different solvents. The rinds and seeds of watermelon fruits were obtained, rinsed, cut into smaller pieces, air-dried, ground into powdery sample, and sieved with 40 mm mesh size. 20 g each of sample was extracted using 200 mL of six different solvents (acetone, chloroform, ethyl acetate, ethanol, methanol and water) for 72 h. Each solvent extract was screened for twelve phytochemicals (flavonoid, phenol, reducing sugar, tannin, saponin, alkaloid, volatile oil, quinone, cardiac glycoside terpenoids, steroids and phlobatannin). The extractive values of watermelon rinds ranged from 1.51±0.26% to 13.56±0.20% while that of watermelon seeds ranged from 3.54±0.16% to 10.17±0.19% in all the six solvents used. Acetone and methanol had the higher extractable phytochemicals (41.67%) in watermelon rinds while methanol, ethyl acetate and ethanol (58.33 – 66.67%) had the highest extractable phytochemicals in watermelon seeds. Water and methanol extracts of watermelon rinds had higher total phenol, DPPH and Iron (Fe2+) chelation assay than raw sample of watermelon rinds. Water and methanol extracts of watermelon rinds had higher iron (Fe2+) chelation assay and ferric reducing antioxidant power (FRAP) than raw sample of watermelon seeds. Methanol extract of watermelon seeds had higher total flavonoid, total phenol and DPPH than raw sample of watermelon seeds.