Accelerated Shelf-life Prediction and Quality Characterization of Edible Cotton, Peanut and Soybean Seed Oils Produced in Ethiopia
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Date
2017-10-23
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Addis Ababa University
Abstract
Edible oils are regarded as an important component of the diet because they are source of energy, essential fatty acids, and also provide characteristic flavors and textures to foods. The purpose of this research study was to determine the qualities of edible cottonseed, peanut and soybean oils processed in Ethiopia and predict their shelf-life using ASTM. The AOAC method of Analysis was employed in the determination of the physical and chemical characteristics of the oils. The result obtained for edible soybean, peanut and cottonseed oils, respectively were; specific gravity at 20/20OC: 0.929, 0.943 and 0.922, refractive index at 20OC: 1.48850, 1.48508, and 1.48565, photometric color index: 5.262, 15.908 and 216.316, insoluble impurities: 0.001, 0.004, and 0.013% (w/w), moisture content: 0.210, 0.219 and 0.220% (w/w), peroxide value: 1.299, 2.398, and 3.396meq O2/kg of oil, iodine value: 136.740, 97.536 and 101.112grams of iodine absorbed/100g oil, Saponification value: 210.345, 210.779 and 208.411mgKOH/g, unsaponifiable matters: 0.169, 0.069 and 0.383% (w/w), and acid value: 0.420, 0.630 and 0.561mgKOH/g. Fatty acid profiles were also determined by GC-MS as methyl esters. The results showed that the predominant fatty acid in edible soybean and cottonseed oils was linoleic acid 42.807 and 41.587%, respectively while oleic acid (46.252%) was major fatty acid in edible peanut oil. The shelf-life of edible oils was tested applying ASTM. The oils were subjected to three different elevated temperatures: 35, 45 and 55OC in acceleration chamber and hydrogen peroxides formation were monitored for six successive weeks. The evaluation was performed graphically (fitting of experimental data to a linear equation) after completion of the experiments. Accordingly, the model that best fitted the experimental data corresponds to a zero order kinetic model for all edible oil investigated. Arrhenius relation was applied to model that effect of temperature on the rate constant of peroxide formation. Combining the kinetic model identified and the rate constant model equation, a general shelf-life model equation that could help to predict the shelf-life of oils studied at any temperature was developed. Employing predictive model developed, the shelf-life of the domestic edible oils was determined at room temperature (25OC) and amounts 36.9 weeks for soybean oil, 42.1 weeks for peanut oil and 37.8 weeks for cottonseed oil. The result obtained for most physicochemical quality parameters of the edible oils considered were within the standard range indicated by Ethiopia Standard Agency. From fatty acid profile analysis it can be concluded that edible soybean, peanut and cottonseed oils are an excellent source of essential fatty acid omega-6 (linoleic acid) and omega-9 (oleic acid). Comparatively edible peanut oil had longer shelf-life than edible soybean and cottonseed oils. The shelf-life of properly refined edible oils is typically 12 – 18 months at ambient temperature. From shelf-life assessment, all edible oils investigated scored lower shelf-life. So, to minimize the oxidation of edible oils and maximize the shelf-life, it is recommended to use: antioxidants, sequestering agents and selection of appropriate packaging material (colored glass bottle). Besides, FFAs are more susceptible to oxidation than the glycerol esters of these fatty acids. Therefore, any increase in the acidity of the oil must be absolutely avoided during refining of the oil.
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accelerated shelf-life determination, edible oil quality parameters, oxidation