Crystallization and transformation of polymorphic forms of trioleoyl glycerol (OOO) and 1,2-dioleoyl-3-rac-linoleoyl glycerol (OOL)

Abstract

This study examined the influence of different thermal treatments on the crystallization and transformation of trioleoyl glycerol (OOO) and 1,2-dioleoyl-3-rac-linoleoyl glycerol (OOL). Two triacylglycerol (TAG) samples were cooled at 0.5-15 °C·min-1 and heated at 2 and 15 °C·min-1. The polymorphic characteristics of the two TAGs were analyzed in situ using differential scanning calorimetry, Raman spectroscopy, and synchrotron radiation X-ray diffraction. Multiple polymorphic forms were identified in OOO (α, β′2, β′1, β2, and β1) and OOL (α, β′2, and β′1). Larger quantities of more stable forms (e.g., β2 and β1 of OOO and β′1 of OOL) were obtained when the samples were slowly cooled and heated. In contrast, less stable polymorphs were obtained with increased cooling and heating rates. Polymorphic transformations occurred in either solid-state or melt-mediation and were influenced by heating rates. The results were analyzed by considering the activation energies for crystallization and transformation of stable and less stable polymorphic forms in comparison with previous studies on 1,3-dipalmitoyl-2-oleoyl-glycerol and 1, 3-dioleoyl-2-palmitoyl-glycerol.