NIR-measurements of moisture changes in foods

Mass transfer and especially the movement and loss of water are important for the quality of cooked foods. Measurements of the water content changes during cooking are therefore valuable when it comes to controlling cooking processes. A near infrared reflection fibre optic probe is here used to measure water content changes inside pork meat and buns during heating. The results are compared with a moist porous brick (in the following called model food). Five different periods were seen locally in the centre. First a period of constant water content, then a period of constant decrease (constant rate period). The constant rate was followed by a period, an intermediate period where the temperature levelled at 100°C, while the water content decrease was small. In the fourth period the slope of the water content vs time curve became steeper and the temperature began to increase above 100°C. Finally, the water content moved to zero while the temperature rose towards the air temperature. The results for buns indicated that the water content near the surface began to decrease almost instantly and continued for the whole heating time in a falling rate manner. At the centre, the water content fell initially and then levelled. The major difference compared to the model food was the levelling off temperature, roughly 100°C in the food and 75°C in the model food.