Nature and dynamics of monostearin phase transitions in water: stability and the sub-α-gel phase

Abstract

This work examines the polymorphic transition of a glycerol monostearin–water system (GMS–water) stored at 5 °C, 25 °C and 45 °C for 100 days. Upon addition of co-emulsifiers, such as sodium stearoyl lactylate (SSL), the GMS–water system forms a metastable α-gel structure, which transforms into a coagel structure over time. The GMS–water system loses its water swelling capacity during the polymorphic transition from the α-gel phase to the coagel phase. Therefore the α-gel phase is a more favorable structure for water structuring. Powder X-ray diffraction (XRD), XRD with temperature control, differential scanning calorimetry (DSC), and microscopy were used to examine the nature and dynamics of the phase transition. Results suggest that the α-gel phase is stable for 100 days when stored at 5 °C. Increasing the storage temperature will increase the rate of transformation from the α-gel phase to the coagel phase. However, even though no phase transformation from the α-gel phase to the coagel phase took place, seemingly, fractionation took place within the α-gel structure when stored at 5 °C, altering the melting profile of the gel and affecting the calculation of the Coagel index. The GMS–water system forms a thermally reversible and metastable sub-α-gel phase when cooled below 13 °C. This work characterizes the XRD diffraction patterns and the DSC melting profiles of the sub-α-gel phase of GMS–water system for the first time. XRD patterns suggest that the water layer thickness in the sub-α-gel phase is ∼140 Å. This thick layer of water may contribute to the high water swelling capacity and stability of the monoglyceride–water system at refrigeration temperatures.