J. Appl. Environ. Biol. Sci., 4(11S)28-32, 2015 © 2015, TextRoad Publication ISSN: 2090-4274 Journal of Applied Environmental and Biological Sciences www.textroad.com * Corresponding Author: Mohsen Abedi Gonabad, Graduate student of chemical engineering, Islamic Azad University, Shahroud branch, mohsenabedigonabad@yahoo.com Estimation of Kinetic Parameters of Walnut Oil Using Rancimat Test Mohsen Abedi Gonabad a ٭ , Mostafa Shahidi Noghabi b , Razieh Niazmand b a Graduate student of chemical engineering, Islamic Azad University, Shahroud branch, b Department of Food Chemistry, Research Institute of Food Science and Technology, PO Box 91735-147, Mashhad-Quchan Highway, Mashhad, Iran Received: October 29, 2014 Accepted: December 31, 2014 ABSTRACT In this paper, walnut oil at four different temperatures (353, 363, 373 And 383 ̊ K) were oxidized under the rancimat test conditions, it was observed that the rate of oxidation increases with increasing temperature. The natural logarithm of the reaction rate constant (k) had a linear relationship with temperature changes, according to the Arrhenius equation and activated complex theory, reaction rate constant (A), energy of activation (E a ), Q10 value, enthalpy (∆H ++ ), entropy ( ∆S ++ ) was used to assess oxidative stability of walnut oil, the values of A, E a , Q10, ∆H ++ , ∆S ++ was 2.78 ⨯ 10 13 (per hour), 80.32 (kJ /mole), 2.077, 77.27(kJ /mole), -55.76 joule per mole kelvin, respectively. KEYWORDS: Kinetic parameters, oxidative stability, rancimat, walnut oil 1 INTRODUCTION Foods, because of their nature, as well as a biochemical reactive system, undergo biochemical and physical changes during maintenance and processing and their quality can be changed. The study of these reactions can help identify the most influential factor in determining the quality [18]. Vegetable oils undergo desirable and undesirable changes where these changes depends on chemical compositions (fatty acid structure, the number and position of double bonds, peroxide, chelating compounds and antioxidants), and environmental factors (oxygen, moisture, heat and light) [7]. The oxidation of fats and edible oils is one of the most important reactions that may cause deterioration of the quality of the oil. Rancimat was one of tests that developed fasters for testing the resistance to oxidation of fats. All of these methods include the use of high temperatures, because it is clear that the reaction rate is correlated with temperature [13]. Among them, rancimat test, due to its ease of use and repeatability, has become a popular method used nowadays [15-14]. Rancimat test allows estimating induction period (IP) or oxidative stability index (OSI) which is the period before oil rapid oxidation [1,3]. To design an effective solution to prevent the development of oxidative reactions in food and biological systems, knowing the nature of these reactions and how they are affected by controllable chemical and physical factors is essential. This goal can be achieved through study of reaction kinetics as well as mechanism and energy aspects of these reactions. Kinetics basics deal with the rate of chemical reactions [1,9]. A good understanding of the kinetics of oxidation in vegetable oils can enhance the ability to formulate food products and minimizing undesirable products. Kinetic data are essential for prediction of oxidative stability of vegetable oils at various temperatures, storage and distribution conditions. However, regarding the oxidation of oils and fats, not enough attention is paid to these data [17]. In most of the cases, oxidative reactions have complex and unique behaviors. Therefore, for each product and oil system a separate and an appropriate model must be determined [4]. Through the kinetics of the reactions, two aspects are being studied, first is the speed at which the reaction occurs, and then the factors affecting the reaction (mainly temperature, concentration of reactants and processing and the presence of a catalyst) [12]. Rancimat device determines secondary volatile compounds resulted from lipids oxidation. Volatiles are trapped in deionized water and the increase in water conductivity is measured and is plotted versus time curve. Induction time is the elapsed time to reach the point of failure in the electrical conductivity versus time curve and is defined as an indicator of oxidative stability. [16-6] OSI is determined at different temperatures and therefore can study relative oxidative stability of edible fats and oils in a wide range of temperatures. A number of kinetic parameters can be determined under rancimat test conditions. These are very useful data, to predict the evaluation of vegetable oils under different heat treatment, storage, distribution process [10]. Temperature is the most important external factor affecting the quality and the shelf life of food. Therefore, knowing how temperature affects the reaction kinetics is essential. Many scientists use Arrhenius model and activation energy derived from it. Arrhenius model is a simple yet highly accurate method [8]. Therefore, the purpose of this study was to determine the relative oxidation of walnut oil and oxidation kinetic parameters under rancimat test. 28