A Characterization of the Phase Transitions in Saturated Monogalactosyldiacylglycerol-Water Systems Using Real-Time X-Ray Diffraction Methods

Abstract

Abstract The phase behavior of fully saturated monogalactosyldiacylglycerol prepared from total polar lipid extracts of spinach leaves and dispersed in excess water has been examined by X-ray diffraction methods Synchrotron radiation was used to determine the real-time structural changes in transitions between the different phases driven by temperature scans of the speed conventionally used in differential scanning calorimetry. The high-temperature α-phase of the lipid recorded at 84°C gave rise to a single, rather broad low-angle Bragg reflection at about 2.8 nm and a broad reflection at 0.48 nm indicating that the hydrocarbon chains were in a disordered configuration. Freeze-fracture electron microscopy of the α-phase was found to be consistent with an amorphous phase formed directly from gel-phase bilayers upon heating above the gel to liquid-crystalline phase transition temperature. The α-phase transforms to the lamellar-β phase on cooling i.e. a liquid-crystalline to gel-phase transition; there was n...