EFFECT OF ROASTING TEMPERATURE AND EXTRACTION TIME ON YIELD AND QUALITY OF SOLVENT-EXTRACTED WATERMELON (Citrullus Lanatus) SEED OIL

Abstract

Watermelon seeds are the most nutritious seeds. It might produce oil but is typically discarded as food waste once the fruit is consumed. This study aimed to determine how extraction time and roasting temperature influenced the yield and quality of hexane-extracted watermelon (Citrullus lanatus) seed oil. The experiment was designed with two factors, namely roasting temperature with three levels (100, 130, and 1600C) and extraction time with three levels (2, 4, and 6 hr). Nine treatment combinations and the control were evaluated using a full factorial design with three replications. Watermelon seeds were roasted in a hot air oven for 20 minutes, while unroasted seeds were the control. The oil extraction was carried out using hexane. The results indicated that the physical properties of raw watermelon seed were recorded as 9.33 mm in length, 5.51 mm in width, 2.24 mm in thickness, 5.69 mm of arithmetic mean diameter,4.87 mm of geometric mean diameter,52.14% of sphericity,28.970 of angle of repose,412.27 kg/m3 of bulk density, 750.33 kg/m3 of true density,45.39% of porosity, and 6.65% of moisture content. The proximate compositions of watermelon seed obtained were, 4.54% of moisture content, 24.90% of crude protein, 26.10% of crude fat, 29.00% of crude fiber, 12.45% of utilizable carbohydrate, and 3.00% of ash content. The extraction conditions in this study which resulted in a maximum oil yield of 38.60%, extraction efficiency of 96.49%, and extraction loss of 3.81% were 4 hr and 1600C. Thus, roasting temperature and extraction time had a significant (P<0.05) impact on the extraction parameters such as oil yield, extraction efficiency, and extraction loss of watermelon seed oil and the various physiochemical characteristics of the extracted oil, including viscosity, specific gravity, refractive index, moisture content, free fatty acids, iodine value, acid value, smoke point, saponification value, peroxide value, and pH. The following values were obtained for oils extracted at the above indicated conditions of 160°C and 4 hours: 51.17 CP of viscosity, 0.898 of specific gravity, 1.438 of refractive index,1920C smoke point, 0.68% moisture content, 5.50 mgKOH/g acid value, 2.75% of free fatty acid, 94.10 gI2/100g iodine value,11.83 meqO2/kg peroxide value,192.33 mgKOH/g saponification value, and pH value of 4.61. The results recorded for the color value were 13.27 for L*, 3.16 for a*, and 8.24 for b*. The majority of the physicochemical values, as determined by the study, were almost consistent with the WHO/FAO threshold levels of (IV (110-143 gI2/100g), RI (1.465-1.480), PV (10-15 meqO2/kg), SV (190-200 mgKOH/g), and SG (0.88-0.94)) for crude oil. Generally, this study provided important information for anyone developing products in food production, and the optimum roasting temperature and extraction time were resulted in increased yield and quality of extracted watermelon seed oils, which helps a promising and sustainable approach to utilize waste product.