INVESTIGATION OF THE GEL TO COAGEL PHASE-TRANSITION IN MONOGLYCERIDE-WATER SYSTEMS

The gel to coagel phase transition of monoglyceride-water systems has been studied by nuclear magnetic resonance and differential scanning c alorimetry. It is shown that the molecular arrangements within the bul k beta-crystal of monoglyceride and the coagel phase are identical. Th e mobility of the glycerol backbone is high in the gel phase. On a dec rease of temperature the mobility drops and then crystallization of th e gel into a coagel phase takes place where hydrogen bonds among the g lycerol groups are formed. A prerequisite for this is that D and L iso mers of monoglyceride rearrange within the bilayers through chiral dis crimination. The gel to coagel transition can be discussed in the fram e of the Avrami theory of crystallization kinetics. The values of the Avrami exponent indicate a transition from a 2-dimensional to a 3-dime nsional crystal growth on increasing the monoglyceride concentration. In the case of a 2-dimensional crystal growth the phase transition is diffusion controlled. Moreover, on applying shear to the gel phase, th e phase transition evolves from a random so a spontaneous nucleation m echanism.