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 calorimetry. It is shown that the molecular arrangements within the bulk beta-crystal of monoglyceride and the coagel phase are identical. The mobility of the glycerol backbone is high in the gel phase. On a decrease of temperature the mobility drops and then crystallization of the gel into a coagel phase takes place where hydrogen bonds among the glycerol groups are formed. A prerequisite for this is that D and L isomers of monoglyceride rearrange within the bilayers through chiral discrimination. The gel to coagel transition can be discussed in the frame of the Avrami theory of crystallization kinetics. The values of the Avrami exponent indicate a transition from a 2-dimensional to a 3-dimensional 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, the phase transition evolves from a random so a spontaneous nucleation mechanism.