Boleslaw Kowalski

Determination of oxidattve stability of edible vegetable oils by pressure differential scanning calorimetry

Abstract Rapeseed, soybean, corn and sunflower oils were oxidized in the cell of a pressure differential scanning calorimeter (PDSC). From the resulting PDSC exotherms the characteristic parameters were extracted and used for assessment of the oxidative stabilities of the oils. Sunflower oil appeared to be the least stable. The resistance of the other oils to oxidation depends on temperature. At 110°C their stabilities are almost the same, but at higher temperatures corn oil is less stable than rapeseed or soybean oil, whereas at lower temperatures this sequence is reversed. As PDSC exotherms were obtained at different temperatures, equations for extrapolation of the PDSC parameters have been proposed and activation energies for oxidation of the oils have been calculated.

Thermal-oxidative decomposition of edible oils and fats. DSC studies

Abstract The DSC scans of edible vegetable oils and of lard were measured by heating the samples up to 360 °C in an atmosphere of oxygen. The heating rates were in the range 5–20 °C min−1. From the resulting DSC exotherms, their extrapolated onset and peak maximum temperatures were determined and used for the assessment of thermal-oxidative stabilities of the samples and for calculation of activation energies. Two samples of highly rancid rapeseed and sunflower oils and eighteen samples of rapeseed oil inhibited with 2-(-butyl-4-methoxyphenol, 2,6-di-t-butyl-4-methylphenol and propyl gallate were also studied. The onset oxidation temperatures of rancid oils were lowered by about 30–40 ° C compared with fresh oils. An improvement in the thermal-oxidative stability of inhibited rapeseed oil, judged from the onset oxidation temperatures, depends on the antioxidant used. For 2-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-methylphenol, this improvement was practically negligible, but for propyl gallate a substantial increase in the stability of rapeseed oil was found.

Kinetics of rapeseed oil oxidation by pressure differential scanning calorimetry measurements

Samples of rapeseed oils were oxidized at isothermal conditions in the cell of a pressure differential scanning calorimeter (PDSC). The experiments were carried out under 1400 kPa oxygen pressure at a temperature in the range of 113—144 °C. From resulting PDSC exotherms the times to reach the peak maximum (τmax) were determined and used for the assessment of the oxidative stabilities of the samples. As PDSC exotherms were obtained at different temperatures, equations for extrapolation of the τmax values were proposed and activation energies as well as specific rate constants for oxidation were calculated.

Monitoring of rapeseed oil autoxidation with a pressure differential scanning calorimeter

Abstract Samples of rapeseed oils stored at room conditions were used for determination of peroxides values (PV) by iodometric titration and for thermoanalytical parameters ( t ON and t max ) determined with a pressure differential scanning calorimeter when used in the isothermal mode. The assessment of oxidative stabilities and the anticipation of the oxidative fate of oils based on a single PV or on t ON and t max determination is rather uncertain. The linear correlation of t ON and t max vs. PVs makes possible a comparative assessment of the oxidative stabilities of the oils studied. Such assessments can be performed only for oils not reprocessed which show PV ≤ 30 mmol O 2− 2 /kg of oil. The use of pressure differential isothermal calorimetry enables a more rapid stability assessment than the use of PV measurements alone.

Oxidative stabilities of engine oils contaminated by vegetable oil

Abstract Samples of engine oils of CC or CD API grades contaminated with edible rapeseed oil (2–;10%) have been oxidized in the cell of a pressure differential scanning calorimeter (PDSC). The PDSC experiments were carried out under 1400 kPa oxygen pressure at 190°C. From the resulting PDSC exotherms their extrapolated onset and peak maximum times have been determined and compared with results obtained under the same conditions for engine oils without addition of vegetable oil. The presence of rapeseed oil in engine oils drastically decreases their resistance to oxidation.

Evaluation of the stability of some antioxidants for fat-based foods

Abstract This paper discusses the evaluation of the stabilities of 2-t-butyl-4-methoxyphenol, 2,6-di-t-butyl-4-methylphenol and propyl gallate, which are frequently incorporated as antioxidants in fat-based foods. The stability of an antioxidant depends upon its volatilization, thermal decomposition and oxidation. The results of investigations performed by differential scanning calorimetry, pressure differential scanning calorimetry and thermogravimetry have shown that the stabilities of the materials studied increase in the above-mentioned order of antioxidants.

Determination of spontaneous ignition temperatures of edible oils and fats by pressure differential scanning calorimetry

Abstract Samples of vegetable, edible oils and animal fats were intensively oxidized in the cell of a pressure differential scanning calorimeter (PDSC). At high oxygen pressures (800–2800 kPa) and at high heating rates (40–90°C min−1) the samples undergo spontaneous ignition. The temperatures at which ignition occurs were determined from PDSC scans. The influence of heating rate, pressures of oxygen and presence of copper on spontaneous-ignition temperatures for the studied oils and fats are discussed.