COMPARATIVE STUDIES ON THE BIOACTIVITY OF SOME NUTRACEUTICAL COMPONENTS OF VARIOUS PARTS OF WATER MELON (Citrullus lanatus M.)

Abstract

Amino acid, vitamins A, B(B1, B2 and B3), C and E, total phenol, total flavonoid components, as well as the antioxidant activities and enzyme inhibitory properties of various parts (red pulp, white pulp, seeds and bark) of water melon (Citrullus lanatus) were analyzed and compared. Aqueous extracts of various part of water melon were prepared after freeze-drying of the samples. Arginine, glutamic acid, leucine, lysine, isoleucine, phenylalanine, tryptophan, valine, methionine, proline, arginine, tyrosine, histidine, cystine, alanine, glycine, threonine, serine and aspartic acid were some of the amino acids that were distributed in various part of the samples. All parts contained vitamins A, B(B1, B2 and B3), C and E in various amounts, with the white pulp showing the highest content (787.1 ± 5.6 units/g, 0.7 ± 0.0 mg/g, 0.8 ± 0.0 mg/g, 0.3 ± 0.0 mg/g, 67.8 ± 0.1 mg/g, 0.4 ± 0.0 mg/g) respectively, and the bark showing the lowest content (401.8 ± 0.1 units/g, 0.3 ± 0.00 mg/g, 0.3 ± 0.0 mg/g, 0.0 ± 0.0 mg/g, 30.5 ± 0.0 mg/g, 0.0 ± 0.0 mg/g). Moreso, the bark & seeds and seeds & white pulp had the highest total phenols and total flavonoids content respectively. The antioxidant properties of the extracts such as Fe2+ chelating ability, hydroxyl and 2,2’-azinobis (3- ethylbenzo-thiazoline-6-sulfonate) [ABTS] radical scavenging abilities and inhibition of lipid peroxidation as well as the in-vitro assessment of the inhibitory activities of extract on acetylcholinesterase (AChE) were also assessed. All parts of Citrullus lanatus had good antioxidant activities as typified by high ABTS+ and hydroxyl radicals scavenging capacities, ferric reducing antioxidant ability, Fe2+ chelating ability and inhibition of lipid peroxidation. The results revealed that white pulp and seeds of water melon showed the strongest AChE (IC50 =58.60 ± 0.43μg/ml) inhibitory activity. The antioxidant and enzyme inhibitory properties of water melon could partly be linked to some antioxidants and amino acids distributed in the samples. The results obtained from this study indicate the biological importance and possible utilization of the various fruit parts of water melon as nutraceuticals for prevention/management of cardiovascular and related ailments, however, the bark, white pulp and seeds of water melon appear to be more effective than the usually consumed red pulp.