USE OF NUCLEAR-MAGNETIC-RESONANCE TO MODEL THERMOPHYSICAL PROPERTIES OF FROZEN AND UNFROZEN MODEL FOOD GELS

This study deals with the measurement and the modelling of the heat ca pacity of model food gels in frozen or unfrozen states. To improve the modelling, the amount of each water stare (ice, freezable water and b ound or unfreezable water) was measured by low-resolution pulsed nucle ar magnetic resonance (NMR) as a function of temperature. The amounts of water bound to each solid were found as 0.66 g g(-1) DM (dry matter ) for agar; 0.05 g g(-1) DM for sucrose; 0.26 g g(-1) DM for starch; 0 .44 g g(-1) DM for gelatin; 0.31 g g(-1) for ovalbumin. Heat capacity values calculated from these results were closer to experimental ones than those obtained from an additive model of the heat capacity when t he water fractions were estimated by the Raoult's law. Besides, the NM R data were used to check some thermal conductivity models of food gel s (the series model, parallel model or Maxwell's one). Generally, the prediction of thermophysical properties was better when the different states of water were determined experimentally by NMR.