Phase Behavior of Monoglycerides in Vegetable and Mineral Oil

Abstract

We studied the phase behavior of 1-myristoyl glycerol (C14), 1-palmitoyl glycerol (C16), 1-stearoyl glycerol (C18), 1-monoarachidate glycerol (C20), and 1-monobehenin glycerol (C22) in vegetable (VO) and mineral (MO) oil using X-ray and DSC analysis. The results obtained showed that the Lα, sub-α1, and sub-α2 transitions observed in the neat C16 to C22 were also present in the corresponding VO and MO solutions (1% to 8% MG). The C14 developed just the Lα and the sub α1 phases, that further transformed into the β phase. The differences between the MGs phase diagrams obtained in the VO and the MO, were mainly associated with the MGs’ polar “head” solubility in the oil as a function of the MGs concentration, as affected by the oil’s relative polarity. Thus, in the VO the phase diagrams of C16 to C22 showed zones where the Lα and sub-α1 phases crystallized concomitantly, affecting the sub-α2 transition temperature. In contrast, in the MO the Lα, the sub-α1, and the sub-α2 phases of C16 to C22 occurred in well-differentiated temperature zones independent of the MG concentration. This is the first report showing that the C16 also develops the sub-α2 phase in the neat state and in VO and MO solutions. Based on the X-ray analysis and through molecular modeling we established that the neat C16 to C22 crystallized in a monoclinic form with a 2L organization. The inclination of the alkyl chain associated with the monoclinic organization, seemed to be a structural requirement for the crystallization of the sub-α2 phase.