The assesment of oxidative stability and melting characteristic of palm oil and cocoa butter

Abstract

Two kinds of fats were investigated in this study: palm oil and cocoa butter. Cocoa butter is one of the most precious and useful vegetable fat obtained from the cocoa beans. Palm oil is an edible vegetable oil high in saturated fats and free of trans fats. A lot of methods for determining oxidative stability are known. Differential Scanning Calorimetry is in the group of thermoanalytical methods and allows the determination of oxidation parameters without the need for chemicals substances. With the use of DSC, polythermal and isothermal research can be carried out. The aim of this research was to analyse the oxidative stability of cocoa butter and palm oil. The kinetics parameters: activation energy (E a ), preexponential factor Z were investigated with used differential scanning calorimetry (DSC). The initial temperature (onset) and maximum temperature (final) of oxidation process, and melting characteristic for both lipids were determined by DSC. The kinetics parameters, temperatures (onset and maximum) were investigated at oxygen atmosphere. The melting characteristic was investigated at nitrogen atmosphere. Calibration was done with indium standards. The averages from measurements of T on and T max for each lipid at a given temperature were determined as the intersection of the extrapolated baseline and the tangent line (leading edge) of the recorded exotherm. The range of temperatures during determine melting characteristic were –80 to 80°C. If the heating rate of the system was constant for the test conditions, then the temperatures obtained: T on and T max were characteristic of the system and could be used as parameters differentiating the resistance (stability) of fats and oils to thermal decomposition. Palm oil was characterized by a lower activation energy at onset temperature than cocoa butter, it may be due to the fact that palm oil was unrefined and had a greater amount of pollutions such as e.g. free fatty acids and incomplete triacylglycerols. The course of melting characteristic for cocoa butter and palm oil were different. The differences in the melting characteristic for the lipids tested can be attributed to their different composition of triacylglycerols.