Comparative Study of Thermal and Structural Behavior of Four Industrial Lauric Fats

The thermal and structural behavior of four industrial lauric fats, sold under the same commercial description, were investigated by using pulsed nuclear magnetic resonance (pNMR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) in order to obtain more basic information about their physical properties and particularly, about their polymorphism. The four fats have been classified into two groups based on their fatty acid (FA) and triacylglycerol (TAG) compositions: group 1 was characterized by its high concentration of stearic acid and group 2 by its high concentrations in lauric and myristic acids. After cooling and 24 h tempering at 4 A degrees C, groups 1 and 2 crystallized in the beta'(2) and beta'(1) forms, respectively. These crystalline varieties corresponded to double-chain-length organizations (2 L) with the long spacing (LS) values around 36.48, 37.43, and 37.65 for group 1, and 33.89, 34.00, 35.04, 37.64, and 37.76 for group 2. During heating from 5 to 50 A degrees C at 5 A degrees C/min, the two groups evolved, respectively, from the 2L beta'(2) or 2L beta'(1) forms to liquid state without going through the 2L beta form, indicating their great beta' polymorph stability. However, after rapid cooling (-25 A degrees C/min), all fats exhibited the same polymorphic evolution; they evolved from the alpha form between -30 and -10 A degrees C to a mixture of alpha and beta'(2) forms with the vanishing of alpha crystal between 10 and 20 A degrees C and that of beta'(2) polymorph at the temperatures above 35 A degrees C. The passage to liquid state was also realized without the occurrence of beta transition. The XRD data were in accordance with DSC melting profiles or with solid fat content (SFC) melting profiles.