Extraction and Characterization of Oil from Watermelon Seed

Abstract

Extraction and characterisation of watermelon seed oil were carried out to investigate the effects of different drying methods and seed size on the quality and quantity of oil from watermelon (Citrullus lanatus) seeds. The watermelon seeds were removed from the pod and washed. The sample was weighed and divided into two equal parts; one part was subjected to sun drying, while the other part was subjected to oven drying (at a temperature of 30 °C). Drying by sun, as expected, was gradual compared to oven-drying, which was faster. The dried seeds (sundried and oven-dried) were dehusked and dry-milled into fine crumbs using a hand-milling machine. The powdered product from the mill was then subjected to oil extraction using hexane as solvent. Proximate and physicochemical analyses of watermelon seeds were carried out. The results showed that the seeds contained 5.15 ± 0.03 % moisture, 4.90 ± 0.14 % ash, 50.48 ± 0.05 % fat, 32.38 ± 0.02 % protein, 6.10 ± 0.02 % crude fibre, and 6.35 ± 0.12 % nitrogen-free extract. Physico-chemical characteristics showed that the pale-yellow oil had a specific gravity of 0.860 ± 0.003 and a refractive index of 1.471. The saponification value was 184.29-187.09 mg KOH/g (for both drying methods). Iodine value was 103.04–115.12 mg Iodine/g (for both drying methods). Acid value was 10.4 – 12.8 mgKOH/g and free fatty acid was 5.2 – 6.4 mgKOH/g (for both drying methods). The peroxide value was 18.74 meq peroxide/g. The watermelon seed can thus be considered a good source of protein with high nutritional value. Many of the physicochemical properties of the seed oil studied were comparable to those of other conventional seed oils, such as soybean, cowpea, and groundnut. The watermelon seed oil, therefore, has potential for use as a domestic and industrial oil.