Fatty acids, heavy metal concentration, and characteristics of selected oil seeds grown in west Nile, Uganda

Abstract

In this study vegetable oils extracted from three types of oil seeds namely; sunflower (helianthus annus), sesame (sesamum indicum) and peanut (Arachis Hypogaea) grown in west nile sub-region were investigated. Fatty acid composition, heavy metal content, cadmium (Cd), zinc (Zn), iron (Fe), lead (Pb) and characteristics of the oils were determined using GC/MS, AAS and AOAC standard methods respectively. Results for fatty acids showed that oleic, linoleic, palmitic, stearic, behenic, lignoceric, and linolenic acids were present in all the oils.The contents of the major fatty acids ranged from (44.06 to 44.12%) oleic, (30.29 to 31.51%) of linoleic, and (10.93 to 13.07%) palmitic acids. This result demonstrates that sesame, sunflower, and peanut oils are of unsaturated type, but belonging to mid-oleic acid subclass. The polyunsaturated to saturated fatty acid ratios of the oils were >1, the minimum recommended by FAO. Results of heavy metal determination revealed that iron and lead were detected in all the oil samples and the concentration ranged from 2.330-14.982mg/kg for iron and 1.944-2.126mg/kg for lead (Pb). The highest concentration of lead ((Pb) and iron (Fe) were in sunflower and sesame oils respectively. Cadmium and zinc were not detected in all the oils.The levels of Lead and Iron were above the maximum permissible limit of (0.1mg/kg) for Lead, and (1.5mg/kg) for Iron, respectively. Heavy Metals like iron (Fe) in vegetable oils enhance the oxidation of fatty acids to esters, which affect the nutritional value and properties of oil. Lead (Pb) is toxic to the body even at a low concentration. Results of the oil quality characteristics showed that the oils exhibited satisfactory results regarding density, viscosity, iodine value, peroxide value, acid value and saponification value. The peroxide value was found in acceptable range of 1.42 to 9.25 meq/kg. While iodine value varied from 79.64 to 126.59gI2/100g. Keywords: Fatty Acids, Heavy Metal, Vegetable Oils, Oil characteristics