A RAPID LOW RESOLUTION PULSE NMR METHOD TO DETECT PARTICULAR WATER MOBILITIES DURING THE DRYING OF CARROTS

A rapid low resolution pulse NMR method to monitor both the longitudinal relaxation time (T1) and the transverse relaxation time (T2) during the drying of foodstuffs is presented. The plot of T1 vs T2 presents a minimum that is almost independent of the temperature from 20 to 30-degrees-C. This T1 minimum could be used for the detection of particular water mobilities, as it corresponds to a water mobility which depends only on the frequency of the NMR apparatus. In the particular case of partially dried carrots, the water content corresponding to the T2 values al this minimum is between 21.1 % and 21.9 % (wet basis). The rapid method (less than 1 min per sample) proposed is based on the estimation of both the T1 and the T2 using the same pulse sequence and only two points in the relaxation curves. The influence of the most important factors (detector mode, audio filter bandwidth, signal to noise ratio enhancement, relaxation delay between repetitions of the pulse sequence and interpulse delay) is discussed in relation to the rapidity and the precision of the method.