Induction Periods for Lipid Crystallization of Various Vegetable Oils

Abstract

INTRODUCTION Lipids have wide applications, including in foods, pharmaceuticals, and cosmetics. In food products, lipids play important roles not only as an essential nutrient for humans 1 but also as a preservative 2 and heating medium 3 5. Furthermore, lipids also improve the taste and texture of food for enrichment of our diet 4, 5. Controlling lipid crystallization is important during lipid refining, and during production and preservation of lipid-containing foods. In the lipid refining process, the precipitation of lipid crystals with a lower liquid-phase content is required to improve refining efficiency 5, 6. The fine appearance and texture of foods with high-lipid content such as chocolate are created by appropriately controlling crystal polymorphism 7. The appearance or texture of dressings and chocolate can be spoiled by crystal growth or polymorphic transition during storage 8, 9. It is also reported that lipid crystallization could affect its oxidation 10. Studies on crystallization behaviors have been focused on many factors, such as the time at which lipid crystallization starts, the crystallization rate, crystalline polymorphs, polymorphic transition, crystal morphology, crystal size,

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

“…When the peak top temperatures of peaks 1 through 3 were extrapolated to a cooling rate of 0 /min, all the peaks intersected the vertical axis at approximately 30 . However, rapeseed oil crystallized even during isothermal storage at 20 or higher 13,27,28 . These facts suggest that the phenomena occurring at the slow cooling rate were significantly different from those occurring during the isothermal storage.…”

“…Such a temperature dependence was specific to peak 1, and it was not recognized in other peaks. The crystallization behavior of rapeseed oil kept isothermally at 17 or lower was previously investigated 13,27,28 . The induction period for crystallization did not simply shorten as the storage temperature decreased, but it showed a unique behavior of extending at approximately 23 .…”

“…The fatty acids contained in rapeseed oil are approximately 65 oleic acid hereinafter, O , 20 linoleic acid L , 8 linolenic acid Ln , 4 palmitic acid P , 2 stearic acid S , and 0.5 arachidic acid 13 . The TAG composition of the oil is approximately 25 for trioleoyl glycerol OOO , 20 for 1,2-dioleoyl-3-linoleoyl glycerol LOO , 11 for 1,2-dioleoyl-3-linolenyl glycerol LnOO , and 8 for 1,2-dilinoleyl-3-olelyl glycerol LLO , and the oil does not include TAG consisting only of saturated fatty acids 29 .…”

“…The crystallization behavior of vegetable oils, such as rapeseed and olive oils, was investigated under an isothermal condition, and it was reported that the time from the start of storage to the start of crystallization at a certain temperature, i.e. the induction period for crystallization, did not decrease monotonously with decreasing storage temperature 13 . This phenomenon is caused by the difference in the crystallization temperature and crystal structure among the TAGs composing the oil 14,15 .…”

“…The crystallization behavior in the constant temperature-decreasing process was significantly different from that in the isothermal storage process. However, the cause for the different crystallization behaviors remains unclear 13 . Since a curve with some peak overlap is obtained in the temperature-decreasing process, the above-mentioned thermal analysis methods cannot be applied directly to the curve.…”