Roselle (Hibiscus Sabdariffa) Seeds and Kernels as a Potential Source of Oil, Protein and Minerals

This study aimed to evaluate Roselle seeds (RS) and Kernels (RK) as an unconventional source of oil, protein, and minerals. The results indicated that RS protein contains a high percentage of essential amino acids (39.47%) compared to that reported by FAO/WHO/UNU (1985) while, methionine and cystine were the limiting amino acids. The proteins were fractionated using SDS-polyacrylamide gel electrophoresis to 10 bands ranged in molecular weight, from 20 to 245 KDa and the main bands had a molecular weight of 180, 135, 100, 63, 48 and 20 KDa. Thin layer chromatographic analysis of the crude RS oil indicated that total lipids consisted mainly of 8 lipid classes of glyceride and nonglyceride compounds in addition to the polar lipids located on the baseline. The identified fractions were: polar lipids, monoacylglycerols, 1,2 and 2,3 diacylglycerols, sterol, 1,3 diacylglycerols, free fatty acids, triacylglycerols and hydrocarbons and sterol esters. Triacylglycerols were the predominant fraction. Gas-Liquid Chromatographic “GLC” analysis of crude RS oil indicated that it composed of the high percentage of unsaturated fatty acids (69.7%) in which oleic acid was 31.27%, while, linoleic acid was37.61%. Saturated fatty acids represented 30.3 % of the total fatty acids. Palmitic acid was the major fatty acid (22.44%) followed by stearic (5.77%). Physicochemical analysis of crude RS oil showed that it had a yellow colour and the Hunter colour components indicated that L*, a*, b* values of the oil were 29.85, 0.94 and 9.94, respectively. It had 1.4724 refractive indexes at 18°C, 0.919 g/cm3 specific gravity, 99.47 iodine value, 194.4 saponification number, 7.52 peroxide value and 0.828 free fatty acids as % oleic acid. RS contained the following minerals: K, Mg, P, Ca, Fe, Cu, Zn. Potassium (1140 mg/100g) was the predominant element in the seeds, followed by phosphorus (482 mg/100g), magnesium (242 mg/100g) and calcium (239 mg/100g). Also, the effect of complete removing of RS hull through water soaking process for different time (10hr-15min) and temperatures (25-75 °C) to obtain Roselle kernel (RK) on the aforementioned analysis was considered. The results indicated that this process had some effects on the protein and mineral composition, while oil composition and it,s characteristics were not affected by this treatment. It could be concluded that RS as a by-product could have the potential for the functional food industry.