Rapid Identification Of Edible Oils Manufactured In Kenya

Abstract

The aim of this research was to develop a rapid identification method of edible vegetable oils manufactured in Kenya. Vegetable edible oils processed and refined in Kenya have not been characterized and hence it‟s impossible to distinguish between them. Sunflower, Corn and Soya bean vegetable oils were analysed for physico-chemical parameters, absorbance in Ultraviolet Visible and in Infrared spectroscopy to establish specific fingerprint. Twenty two samples comprising of nine Sunflower of three different brand type, nine Corn oils of three different brand type and four Soya bean oils of two different brand type were collected from various supermarkets in Nairobi. The samples were transported, prepared and stored in the refrigerator at 4°C. Physico-chemical parameters analysed include Density, Refractive Index, Peroxide Value, Saponification Value and Total Free Fatty Acids. Ultraviolet/visible spectrophotometer at specific wavelengths was used to establish characteristic absorbance of each type of vegetable oil. The Infrared spectroscopy method was subsequently applied to establish specific absorbance characteristic of each vegetable oil at given wavelength. Sunflower oil was found to have Density of 0.9205±0.0025 g/cm3, Refractive index of 1.468 nD ±0.001, Saponification Value of 191±3 mgKOH/g, Peroxide Value of were ≤ 10 mmol/kg and Total Free Fatty Acid of ≤ 0.085%. The Sunflower oil Ultraviolet/ Visible gave absorbance peak of 2.779 ±0.183 at 315.0nm and 2.742 ±0.098 at 300nm wavelength. Corn oil had Density of 0.921±0.004 g/cm3, Refractive index of 1.4665 nD ±0.0015, Saponification Value of 192±5 mgKOH/g, Peroxide Value of were ≤ 10 mmol/kg and Total Free Fatty Acid of ≤ 0.1%. The Ultraviolet/Visible absorbances for Corn oil were 3.019 ±0.082 at 315nm, 3.0725 ±0.0685 at 330nm and 3.034 ±0.181 at 345nm. Soya bean oil had Density of 0.922 ±0.003 g/cm3, Refractive index of 1.468 nD ±0.002, Saponification Value of 192 ±3 mgKOH/g, Peroxide Value of were ≥ 10 mmol/kg and Total Free Fatty Acid of ≤ 0.176%. Soya bean oil the Ultraviolet/ Visible absorbance were at 3.1325 ±0.1235 at 300nm, 3.101 at 315nm and 3.087±0.048 at 345nm. The three vegetable oils were found to have distinct infrared fingerprints. Corn oil had specific peaks at 1150-1130 cm-1 and 1090 cm-1and Soya bean oils had specific peaks of 1100-1090 cm-1 and 900 cm-1. Sunflower oil infrared spectra did not exhibit 1150-1130 cm-1, 1100-1090 cm-1and 900 cm-1 specific peaks which were found in corn and soya bean oil. A protocol that can be used to distinctively analyse Sunflower, Corn and Soya bean oils was developed that is relatively cheaper both in time and resource and applicable by oil manufacturers.