Isothermal crystallization behavior of lard at different temperatures studied by DSC and real-time XRD

Differential scanning calorimetry and real-time X-ray diffraction using synchrotron radiation were used to study the isothermal crystallization formation mechanism of lard at 18, 20, 22 and 24 degrees C. At 18 degrees C, lard crystallized in three steps. A potential mechanism for these three steps was proposed. In the first step, part of the melt (the trisaturated triacylglycerols (TAGs)) crystallized in a crystals adopting a double length structure (2L), while the second step consisted of a polymorphic transition of these 2L alpha crystals to beta' crystals with a triple length structure (3L). Extra 3L beta' crystals consisting of monounsaturated TAGs were also formed directly from the melt. In the third and last step, beta crystals were formed due to a second polymorphic transition of trisaturated 3L beta' crystals to beta crystals adopting a 2L structure. Above a cut-off temperature of 20 degrees C lard crystallized in two steps: no formation of alpha crystals could be observed and 343, crystals (trisaturated and monounsaturated TAGs) were formed directly from the melt. This proposed mechanism implies that lard crystallization is characterized by an overlap of fractionated crystallization and polymorphic transitions. (C) 2014 Elsevier Ltd. All rights reserved: