A differential scanning calorimetry study on the oxidation of C₁₂‐C₁₈ saturated fatty acids and their esters

Abstract

The autoxidation of lauric, myristic, palmitic, and stearic acids, their ethyl esters, and palmitic and stearic triglycerides was investigated by means of the isothermal and nonisothermal differential scanning calorimetry methods under oxygen flow. The activation energies of oxidation of all investigated compounds were similar (106.0-134.3 kJ/mol) and did not depend on length of the carbon chain. Kinetic parameters of start of the oxidation were similar for each investigated fatty acid and ester. Esterification of carboxyl group did not interfere with the reaction rate. The study showed good agreement between isothermal and nonisothermal data.Paper no. J9048 in JAOCS 76, 655-657 (June 1999).There is a considerable interest in characterization of thermooxidative properties of the fatty acids, their esters, and kinetics of their oxidation. Natural fats and oils are very complicated systems of mono-, di-and triglycerides, higher lipids, phospholipids, antioxidants, and other compounds. In the basic research they should be replaced by simple lipid analogs such as free fatty acids and their esters. Although autoxidation of saturated hydrocarbons was the subject of many investigations (1-6) there are only a few papers describing autoxidation of natural saturated fatty acids and their esters. Former studies on autoxidation of saturated normal hydrocarbons suggested the applicability of the results to oxidation of saturated fatty acid esters. Moreover, it was found that autoxidation rates were increasingly proportional to the carbon chain length (1). Recent studies in which overall reactivities of n-paraffins determined by analysis of monoderivatives at the initial stage of oxidation (7) led to conclusion that the reactivity probably does not depend on length of carbon chain. Presence of two maxima on the nonisothermal differential scanning calorimetry (DSC) oxidation curves indicates that thermoxidation can be characterized by at least two-step exothermic effect. Each reaction is characterized by different kinetic parameters. Thus, the kinetic parameters of autoxidation (start of the exothermic process) and destruction of autoxidation products (occurring at higher temperatures) can be determined (8,9). In this study, oxidation of the natural saturated fatty acids: lauric, myristic, palmitic, and stearic, their ethyl esters, and glycerol tripalmitate and tristearate was investigated by DSC methods. The kinetics of the autoxidation of materials containing fatty acids was investigated by thermoanalytical procedures (10-13). However, no data concerning thermoxidative behavior of pure saturated fatty acids and esters have been reported as yet. This study was undertaken in order to establish the kinetics parameters of thermoxidation of these classes of compounds. EXPERIMENTAL PROCEDURESMaterials. The following fatty acids-lauric, palmitic, stearic-and ethyl esters-laurate, myristate, palmitate and stearate (all 99%)-were purchased from Sigma-Aldrich (St. Louis, MO). Purity of glycerol tripalmitate (BDH, Poole, United Kingdom)...

Determination of the oxidative stability of hazelnut oils by PDSC and Rancimat methods

“…Assuming that lipid oxidation of oils in an excess of oxygen is a first-order exothermic process [5,29,30], the kinetic parameters, such as, pre-exponential factors (Z) and activation energies (E a ) for studied oxidation reactions can be calculated based on the Eq. (3) using A and B coefficients and the Arrhenius equation:…”

Application of Differential Scanning Calorimetry (DSC) at the characterization of the virgin olive oil

“…Las muestras se sometieron a un programa de temperatura en el que se ha unificado, en una sola etapa, el proceso de cristalización y fusión (Tan y Che Man, 2000) con el de oxidación (Litwinienko et al, 1999) (Gupta y Jaworski, 1991), consistente en: calentamiento de las muestras desde la temperatura ambiente hasta los 50 o C, bajo una corriente de nitró-geno a 20 mL/min., isoterma a esta temperatura durante 5 minutos e inicio de la rampa de enfriamiento desde los 50 Durante todo el proceso se han recogido los datos de flujo de calor, en mW, en función del tiempo y de la temperatura, a partir de los cuales se han obtenido los valores de los picos de temperatura de las transiciones (Pt), de la temperatura de inicio de la transición (to) y de la temperatura de finalización de transición (te).…”

“…El proceso de autoxidación de los lípidos es un proceso de tipo exotérmico, en el que el calor de reacción generado puede ser medido en función de la temperatura y del tiempo, por lo que puede ser aplicable la CDB (Litwinienko et al, 1999).…”

Antioxidant Activity of a Oryzanols Concentrate by Differential Scanning Calorimetry

“…In order to study the oxidation kinetics and the oxidative stability of various fats, the isothermal and non-isothermal methods can be used (Tan, Che Man, Selamat, & Yusoff, 2002, Rudnik, Szczucinska, Gwardiak, Szulc, & Winiarska, 2000. This is possible because the lipid oxidation process is exothermic, so that the amount of heat released by a sample subjected to said process can be linked to the rate at which it passes (Litwinienko & Kasprzycka-Guttman, 1998;Litwinienko, Daniluk, & Kasprzycka-Guttman 1999;Thurgood, Ward, & Martini, 2007). The original theoretical basis of this method was described by Ozawa (1965) and later by several authors as Shadidi and Wanasundara (1997), Simon (2006).…”

“…In this way, for the isothermal method an oxidation induction time value is defined as OIT (Simon, 2006) whereas for the non-isothermal method an oxidation temperature called OT (Moser, 2009;Dunn, 2005). materials (Litwinienko & Kasprzycka-Guttman, 1998;Litwinienko et al, 1999;Polavka, Paligová , Cvengros, & Simon 2005;Thurgood et al, 2007). …”