Thermal Stability and Kinetic Study on Thermal Decomposition of Commercial Edible Oils by Thermogravimetry (original) (raw)
Related papers
Journal of Agricultural and Food Chemistry, 2009
Thermal decomposition of 12 monovarietal extra virgin olive oils from different geographical origins (eight from Italy, two from Spain, and the others from Tunisia) was evaluated by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses. All extra virgin olive oils showed a complex multistep decomposition pattern with the first step that exhibited a quite different profile among samples. Thermal properties of the two peaks obtained by the deconvolution of the first step of decomposition by DSC were related to the chemical composition of the samples (triacylglycerols, fatty acids, total phenols and antioxidant activity). Onset temperatures of the thermal decomposition transition and T p values of both deconvoluted peaks as well as the sum of enthalpy were found to exhibit statistically significant correlations with chemical components of the samples, in particular palmitic and oleic acids and related triacylglycerols. Activation energy values of the second deconvoluted peak obtained by the application of kinetic procedure to the first step of decomposition were also found to be highly statistically correlated to the chemical composition, and a stability scale among samples was proposed on the basis of its values.
A THERMOANALYTIC AND KINETIC STUDY OF SUNFLOWER OIL
Recently, thermoanalytic methods have frequently been used in the characterization of oils and fats. In this work, thermoanalytic and kinetic parameters of sunflower oils, with and without antioxidants, were evaluated using thermogravimetry / derivative thermogravimetry and differential scanning calorimetry. The thermogravimetric profiles for the sunflower oils had similar characteristics, showing a level stretch indicative of stability up to about 200 o C. Thermal decomposition of these oils occurred in three stages, related to the decomposition of polyunsaturated, monounsaturated and saturated fatty acids, respectively. DSC curves show two events that characterize the polymerization and decomposition of triglycerides. The heat capacities of the sunflower oils, obtained by DSC, showed a good correlation and were dependent on the composition of fatty acids. The kinetic parameters, obtained by non isothermal thermogravimetry by the Coats and Redfern, Madhusudanan, Horowitz and Metzger and Van Krevelen methods, were dependent on the antioxidant used. Increasing the frying time produced a decrease in the onset of thermal decomposition temperature in the sunflower oils analyzed.
Journal of Thermal Analysis, 1995
The kinetics of thermooxidation of edible oils: soybean oil, rapeseed oil, corn and peanut oil was investigated in two ways. The DSC and its pressure version (PDSC) were used for measuremerits under the isothermal and non-isothermal conditions in atmosphere of oxygen. Comparing these two methods for each oil the differences between the values of activation energies were observed. However, mechanism of oxidation in both method was different.
Thermoanalytical, kinetic and rheological parameters of commercial edible vegetable oils
Journal of Thermal Analysis and Calorimetry, 2004
Thermoanalytical, kinetic and rheological parameters of commercial edible oils were evaluated. The thermal decomposition of the oils occurred in three steps, due to polyunsaturated, monounsaturated and saturated fatty acids decomposition, respectively. According to the temperature of the beginning of the decomposition, the following stability order was observed: corn (A)>corn>sunflower (A)>rice>soybean>rapeseed (A)>olive>rapeseed>sunflower (A - artificial antioxidants). Kinetic parameters were obtained using Coats-Redfern and Madhusudanan methods and presented good correlation. According to the activation energy of the first thermal decomposition event, obtained of Coats-Redfern' method, the following stability order is proposed: sunflower>corn>rice>soybean>rapeseed>olive. In relation to rheological properties, a Newtonian behavior was observed and no degradation occurred in the temperature range studied.
Effect of Reheating on Thermophysical Properties of Edible Oil at High Temperature
2016
This paper is focused on the evaluation of thermophysical properties of unheated oil and multiple times heated oils to study the thermal degradation of edible oil which is reheated for very long time and hence assess the quality of reheated oil being used in different first food shops and restaurants. The purpose of this study is to evaluate the changes in different thermophysical properties such as total energy, refractive index and conductivity of reheated edible oils that take place during the reheating of oils, in order to find an easy and cost effective technique for quality testing of edible oils. Study reveals that the refractive index and conductivity of reheated edible oil have increased and the total energy of edible oil has decreased due to reheating at high temperature for long time. Study also indicates that the presence of food contents during the heating of edible oil, affect the thermophysical parameters in some extent.
Kinetic study of thermal breakdown of triglycerides contained in extra-virgin olive oil
Journal of Thermal Analysis and Calorimetry, 2008
Thermal decomposition of extra-virgin olive oil (EVOO) was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG) up to 550°C at different heating rates (from 5 to 12.5°C min -1 ). The thermal degradation study of four unsaturated or saturated esterified C18 fatty acids with glycerol (i.e., glyceryl-tristearate (C18:0), -trioleate (C18:1), -trilinoleate (C18:2) and -trilinolenate (C18:3)) was also carried out under the same experimental conditions.
Study of the behavior of some vegetable oils during the thermal treatment
Study of the behavior of some vegetable oils during the thermal treatment, 2010
Large quantities of vegetable oils are consumed in food preparation, cooking and frying. The evaluation of the quality of vegetable oils is based on the measurement of their phisyco-chemical properties such as density, refractive index, viscosity, acid and iodine numbers. The aim of this paper is to evaluate the variation of vegetable oils quality as a result of thermal treatment. The evaluation is based on the measurement of some important phisyco-chemical properties of vegetable oils, before and after thermal treatment: density, viscosity, refractive index, acid number. Commercialy available olive oil, sunflower oil and corn oil were used in the study. Based on this experimental investigation, there can be predicted the changes in the vegetal oils characteristics and also there can be made correlation between their properties.
Thermal Degradation of Vegetable Oils
Foods
Vegetable oils provide lipids and nutrition and provide foods with a desirable flavor, color, and crispy texture when used to prepare fried foods. However, the oil quality is degraded at elevated temperatures, and thus must be examined frequently because of the damage to human health. In this study, sunflower, soybean, olive, and canola oils were examined, and their properties were measured periodically at different elevated temperatures. The unsaturated triglyceride in oils reacted with the environmental oxygen or water vapor significantly changes in optical absorbance, viscosity, electrical impedance, and acid value. We used defect kinetics to analyze the evolution of these oil properties at elevated temperatures. The optical absorbance, viscosity, and electrical impedance follow the second-order, first-order, and zeroth-order kinetics, respectively. The rate constants of the above kinetics satisfy the Arrhenius equation. Olive oil has the lowest rate of color center and dynamic v...
Chemometric assessment of thermal oxidation of some edible oils
Journal of Thermal Analysis and Calorimetry, 2010
The effect of microwave heating was studied in six varieties of edible oil. Variations in physicochemical properties were observed and compared with the data obtained by hot plate heating. Fourier-transform infrared spectra of the oils showed substantial variations after both types of heating in the region of hydrogen's stretching (C-H) vibration, region of double bond's stretching (C=O), and fingerprint region. The visible spectra of mustard and olive oil showed the reduction in carotenoid, flavonoid, and chlorophyll pigments after heating. The oil samples were discriminated as saturated, monounsaturated, and polyunsaturated fats using chemometric techniques on physical and spectroscopic measurements.
Kinetic Parameters of the Thermal Oxidation and Degradation Reactions in Soybean Oil and Palm Olein
Journal of the Brazilian Chemical Society
Partially hydrogenated soybean oil and palm olein are oils that are widely used in the food industry. Continuous contact with air may cause changes of the triglycerides chemical structure, to eventually produce substances of lower molar masses that may be toxic to mammals. This study aimed to determine the kinetic parameters for the thermal oxidation of these oils and of their residual used oils from the pre-frying industrial step on preparing breaded chicken meat. The main reactions were followed by thermogravimetry (TG) and differential scanning calorimetry (DSC); the formation of the produced substances was monitored by gas chromatography flame ionization detector (GC-FID) and Fourier transform infrared spectroscopy (FTIR). These analyses indicated different chemical pathways, according to the type of unsaturation and changes in the molecular structures of the fatty acids in the oils. From the thermal analysis, more than one decomposition event was observed during the thermal oxidation process. As the soybean oil has a lower oxidation onset temperature than palm olein, it has lower rate of mass loss, with a higher activation energy value.