Analysis of Nonisothermal Crystallization of Rapeseed Oil by Deconvolution of Differential Scanning Calorimetry Curve

Abstract

Crystallization of vegetable oil affects the efficiency of the oil-refining process and the quality of foods containing the oil. However, the crystallization of the oil is a complicated phenomenon. The crystallization behavior of rapeseed oil was investigated using differential scanning calorimetry (DSC) at a cooling rate of 0.5–10°C/min. It was found that multiple crystal structures with a metastable crystal formed at high cooling rates. A deconvolution technique was applied to analyze kinetically the DSC curves with some peaks. Each DSC curve was separated into 3–5 peaks fitted with an asymmetric double sigmoid function and a Lorentz one. Each peak was normalized by its integrated value, and the crystallinity was calculated. Using the crystallinity values, Avrami, Ozawa, and Friedman plots were obtained. The cooling rate was found to affect the crystallization mechanism and triacylglycerol (TAG) composition of the crystal in the separated peak. Even if the peak numbers are the same, the TAG composition of the crystals might be different depending on the cooling rate. Judging from the peak top temperature and area of the separated peaks, trioleoyl glycerol and 1,2-dilinolenyl-3-linoleyl glycerol would be included in crystals in the peaks with the largest and lowest peak top temperatures, respectively. The relationship between the peak top temperature and cooling rate was unique. This suggests that the crystallization behavior during isothermal storage was different from that in a nonisothermal process.