Determination of the Glass Transition Temperature of Food Polymers Using Low Field NMR

This study has shown that the low field NMR technique can be used to investigate the glass transition process in the food polymers. It has been demonstrated that the spin-spin relaxation time constant T_2Sand the spin-lattice relaxation time constant T₁of the tested food polymers (maltodextrin, bread, cake and cracker) changed dramatically when the polymers underwent the glass transition. The approximate temperature at which T_2Sand T₁changed dramatically, could be easily determined using a bilinear regression model, and was found to be very close to the glass transition temperature found by differential scanning calorimetry (DSC) or thermal mechanical analysis (TMA) in this study or literature. The plasticization effect of water on the polymers, an important phenomenon in the glass transition in polymers, was also observed in this study. The characteristic change in relaxation time constants observed by the nuclear magnetic resonance (NMR) technique was attributed to the segmental motion of polymers varying in different physical states.