Effect of Extraction Methods on Physico-chemical Properties of Watermelon Seed Oil

Watermelon (Citrullus lanatus) is one of the most popular species in the family of Cucurbitaceae. The fruits are widely eaten without due regards to the seed which are discarded each year either as cheap animal feed or simply thrown away. It has been advocated that the mesocarp and seeds should be eaten together because of the belief that the seeds are highly nutritious and medicinal but there is dearth of information of the nutritional composition of the seeds especially the fat and oils. This study was carried out to determine the effect of extraction methods on physicochemical properties of watermelon seed oil. The watermelon fruits (306.17 kg) were cut longitudinally and sliced into smaller pieces. The seeds were extracted from the fruits using stainless steel knife. The percentage seed yield was 2.43% of total fruit weight. The proximate composition of the seed showed that they contain 5.88% moisture, 49.34% crude fat, 30.49% crude protein, 6.25% crude fiber, 4.92% ash content and 3.05% carbohydrate. Oil was extracted from the seeds using three methods; a traditional pounding and boiling method, a mechanical expression method and solvent extraction. The crude watermelon seed oil was degummed and bleached. Physicochemical analyses (Acid value, Free Fatty Acid, Saponification value, Peroxide value, lodine Value, Volatile matter, Specific gravity, Refractive index) were carried out on both the crude and refined oils. The solvent extraction method resulted in highest oil yield of 49.65%, followed by mechanical expression (39.52 %) while the traditional method had a yield of 20.10%. The acid value ranged from 0.107 mgKOH/g to 3.217 mgKOH/g for the crude oil and 0.071 mgKOH/g to 2.289 mgKOH/g for the refined oil. The peroxide values ranged from 1.343 to 4.55 meq/kg for the crude oil and 1.207 to 3.967 meq/kg for the refined oil. The refractive index of the crude oil varied from 1.12 to 1.42 and 1.33 to 1.47 for the refined oil. The Saponification number of the crude oil ranged from 216.63 mgKOH/g to 332.203 mgKOH/g and 100 mgKOH/g to 145 mgKOH/g for the refined oil.