A Look into the Arrhenius Equation’s Application on Unrefined Oils Jennifer Vuia

Overview  What are unrefined oils?  Arrhenius Equation Application on various unrefined oils  An Updated Arrhenius Equation  Concluding remarks  Time for Questions

What are unrefined oils?  Oils that have not gone through commercial refining processes Like degumming, neutralization, bleaching, deodorization and hydrogenation  These crude oils can be pressed and filtered at low heat (cold pressed) Allows them to maintain their biologically active antioxidants, phytonutrients, and phenols Fennema O.R, Food Chemistry, 3 rd Ed., 1996, Lydon K., Environmental Nutrition, 2015

What are unrefined oils?  These oils still have more color, stronger flavors, and are more odorous compared to refined oils  Some examples are olive oil, sesame oil, pumpkin seed oil, and pollock oil Fennema O.R, Food Chemistry, 3 rd Ed., 1996

Arrhenius Equation  A formula used to measure the temperature dependence of reaction rates  The main purpose is to collect data at high temperatures that can then be extrapolated to get a rate constant for lower temperatures. Fennema O.R, Food Chemistry, 3 rd Ed., 1996

Arrhenius Equation  Equation k = Reaction rate constant e = Natural log k o (or A)= pre-exponential factor of frequency R = molar gas constant (8.31 J K -1 mol -1 ) T = absolute temperature E a = activation energy (J mol -1 ) Calligaris et al., J Agri Food Chem, 2006, 54,

Arrhenius Equation in different unrefined oils  Extra Virgin Olive Oil (EVOO) EVOO was stored at temperatures ranging from 3 o C to 60 o C with primary and secondary oxidation products being measured Crystallization occurring at low temperatures affected EVOO stability Calligaris et al., J Agri Food Chem, 2006, 54,

Arrhenius Equation in different unrefined oils  Extra Virgin Olive Oil (EVOO) Arrhenius equation was not able to determine oxidation rate under 25 o C due to the liquid/solid phase changes occurring in the oil at reduced temperatures ○ Unsaturated triacylglyceride (TAG) concentration increase and decrease of polyphenols in the liquid phase surrounding the fat crystals were main cause of deviation Calligaris et al., J Agri Food Chem, 2006, 54,

Arrhenius Equation in different unrefined oils  Pollock oil Pollock oil that was treated with very high heat over a period of time experienced higher lipid oxidation rates Arrhenius equation was used to calculate the average activation energy needed for lipid oxidation in relation to temperature Sathivel et al., J Food Engin, 2008,,84;187-93

Arrhenius Equation in different unrefined oils  Pollock oil Fig 3. Viscosity of the oil decreased as temperature increased. This shows that a change in crystallization could have occurred when the “cold” oil was heated, thus changing the state and characteristics of the pollock oil. Sathivel et al., J Food Engin, 2008,,84;187-93

Arrhenius Equation  Issues At lower heat, changes occur in TAG concentration in the liquid phase surrounding the fat crystals in the olive oil, causing an increased viscosity. Calligaris et al., J Agri Food Chem, 2006, 54,

Arrhenius Equation  Issues The TAG and viscosity change is able to affect the kinetics of lipid oxidation in the now partially crystallized lipid matrix. ○ Enzyme activity could be lost ○ Reaction pathway may change ○ The physical state of the system may change (i.e. freezing) Calligaris et al., J Agri Food Chem, 2006; Fennema O.R, Food Chemistry, 3 rd Ed., 1996

Arrhenius Equation  Issues Therefore, there could exist a critical temperature Below which, the Arrhenius equation is not finding the occurrence of temperature-dependent changes in the oil due to crystallization changes. Calligaris et al., J Agri Food Chem, 2006; Fennema O.R, Food Chemistry, 3 rd Ed., 1996

Arrhenius Equation  Issues High heat exposure and subsequent re-cooling will lead to formation of a different (usually more stable) liquid phase Metin et al., Bailey’s Industrial Oil and Fat Products, 2005

Updated Arrhenius Equation  Purpose To accurately describe the temperature dependence of the oxidation rate by taking into account the changes in the physical state of the oil Calligaris et al., J Agri Food Chem, 2006, 54,

Updated Arrhenius Equation  Same k, R, T, E a  Updated Δk : a corrective factor that takes into account the influence of variables (other than temperature) that significantly affect the reaction rate in the partially crystallized matrix Calligaris et al., J Agri Food Chem, 2006, 54,

 The Δk must be changed according to the oil due to different mechanisms occurring in different oil types Example: ○ Δk for sunflower oil= C oil η C oil = the concentration factor of the liquid phase η = the viscosity ○ Δk for olive oil= C oil C phenol C phenol = the concentration factor of phenols in oil and in the liquid fraction at a selected temperature Updated Arrhenius Equation Calligaris et al., J Agri Food Chem, 2006, 54,

Concluding remarks  The Arrhenius equation has some limitations  While a modified equation has been made, it must be adapted to each oil it is being applied to  More studies must be done to ensure that this is a valid method of stability estimation Calligaris et al., J Agri Food Chem, 2006; Fennema O.R, Food Chemistry, 3 rd Ed., 1996

Questions? ? ? ? ?

References  Calligaris S., Sovrano S., Manzocco L., Nicoli M.C.. Influence of Crystallization on Oxidative Stability of Extra Virgin Olive Oil. J Agric Food Chem, 2006, 54;  Fennema O.R.. Food Chemistry, 3 rd edition. New York: Marcel Dekker,  Lydon, K. The Skinny on Unrefined Plant Oils. Environmental Nutrition: The Newsletter of Food, Nutrition, & Health, 2015, 38(1); 1.  Metin S., Hartel R.W. Crystallization of Fats and Oils. Bailey’s Industrial Oil and Fat Products,  Sathivel S., Huang J., Prinyawiwatkul W. Thermal properties and applications of the Arrhenius equiation for evaluating viscosity and oxidation rates of unrefined pollock oil. J Food Engin, 2008, 84;