Analysis on internal moisture changes of carrot slices during drying process using low-field NMR

In order to investigate the characteristics of internal moisture change of carrot slices at different temperatures during drying process, an hot air drying experiment on carrot slices using the electric heating thermostatic drying oven at different temperatures, which were respectively 40, 50, 60, 70 and 80℃, have been carried out. The internal moisture changes from the perspective of transverse relaxation time (T2) inversion spectrum of low-field nuclear magnetic resonance were analyzed. Results showed that moisture states and moisture distribution changed in drying process and the moisture with high degree of freedom moved to the moisture with low degree of freedom. The drying rate was accelerated with the rise of drying temperature, however, the drying rate was restrained because the material surface crusting hindered the outmigration of water at 80℃. This research can provide theoretical basis for drying technology and conversion point of variable temperature combination drying of fruits and vegetables.