Abstract
Thermal behavior of palm stearin (PS) and palm olein (PO) was explored by monitoring peak temperature transitions by differential scanning calorimetry (DSC). The fatty acid composition (FAC), isothermal crystallization kinetics studied by pulsed Nuclear Magnetic Resonance (pNMR) and isothermal microstructure were also compared. The results indicated that the fatty acid composition had an important influence on the crystallization process. PS and PO both exhibited more multiple endotherms than exotherms which showed irregular peak shapes. An increasing in cooling rate, generally, was associated with an increase in peak size. Application of the Avaimi equation to isothermal crystallization of PS and PO revealed different nucleation and growth mechanisms based on the Avrami exponents. PS quickly reached the end of crystallization because of more saturated triacylglycerol (TAG). The Avrami index of PS were the same as PO under the same isothermal condition at lower temperatrue, indicating that the crystallization mechanism of the two samples based on super-cooling state were the same. According to the polarized light microscope (PLM) images, crystal morphology of PS and PO was different. With the temperature increased, the structure of crystal network of both PS and PO gradually loosened.
Highlights
Palm oil is extracted from the mesocarp of the fruit of the oil palm Elaeis guineensis
In the dry fractionation process, according to the differences in melting points of TAGs, palm oil can be fractionated into many components containing liquid fractions which can be used as cooking and salad oils, and harder fractions which have applications as ingredients of frying fats, margarines, shortenings, as well as specialty fats [4]
As indicated in the images, palm stearin (PS) showed different crystal morphology compared to palm olein (PO) at the same temperature
Summary
Palm oil is extracted from the mesocarp of the fruit of the oil palm Elaeis guineensis. In the dry fractionation process, according to the differences in melting points of TAGs, palm oil can be fractionated into many components containing liquid fractions (oleins, super oleins and top oleins) which can be used as cooking and salad oils, and harder fractions (stearins and mid fractions) which have applications as ingredients of frying fats, margarines, shortenings, as well as specialty fats [4]. Palm stearin and palm olein manufactured by dry fractionation have different triacylglycerol compositions, resulting in oil-based margarine and shortening to present complex crystallization behaviors and different physical properties. Braipson-Danthine and Gibonb pointed out that there was a clear relationship between TAG composition, melting properties and polymorphic behavior and of palm oil and fractions after analyzing a series of palm oil, solid and liquid fractions (stearins, mid fractions, oleins and superoleins) [6]. Their non-isothermal crystallization respectively at a cooling rate of 1, 5, 10 and 20 °C/min was tested
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