A Survey of the Bio-activity of the Fruit Rind of Kiwano (Cucumis metuliferus)

Background: Kiwano, commonly called horned melon is a common fruit consumed in the tropics for its nutritional and therapeutic value. This study evaluated the composition of some bioactive compounds in the rind of the fruit as well as its antioxidant and anti-inflammatory effects using in vitro methods.

Methods: The rind of the fruits of kiwano were peeled out, pulverized and extracted with 80% ethanol. The bioactive compounds evaluated were phenol, flavonoid, beta carotene, lycopene and ascorbic acid. The antioxidant properties were evaluated using DPPH, iron reducing power and inhibition of lipid peroxidation assays. Ascorbic acid served as the standard. The anti-inflammatory property was measured in-vitro using anti-proteinase activity, inhibition of albumin denaturation and membrane stabilization assay systems. Aspirin and diclofenac served as reference drugs

Results: Phenol and flavonoids were the bioactive compounds found in higher concentration than the rest with concentrations of 261.73±13.54 and 130.86±9.66 mgGAE/ml of the dry matter respectively. In the antioxidant assay, the highest activity of more than 50% was recorded in DPPH assay. The maximum percentage radical scavenging activity of the extract was 76.74% at 800 µg/ml with a drop in activity at 1000 µg/ml (75.02%) and EC50 value of 230 µg/ml. Ascorbic acid exhibited 96.35% scavenging activity of radicals at 1000 µg/ml and EC50 value of 260 µg/ml. For the anti-inflammatory assay, the extract exhibited 16.43% anti-proteinase activity, 25.64% inhibition of heat-induced haemolysis activity and 47.14% inhibition of albumin denaturation activity at 1000 µg/ml. More than 50% activity was recorded for the reference drugs.

Conclusion: We therefore conclude that the rind of the fruit of kiwano is rich in biologically active compounds and has antioxidant and anti-inflammatory properties. The rind is a potential source of therapeutic compounds.