ABSTRACT
Objective To study the moisture transfer laws of Chaenomeles sinensis in different drying processes. Methods Using the non-destructive and non-invasive technique of low field-nuclear magnetic resonance (LF-NMR), the transverse relaxation time (T2) inversion spectrum of C. sinensis slice was monitored under different drying methods (hot air drying, drying after evaporation, segmental drying and drying in the shade) to analyze the changes of moisture migration. Results There were three different types water that were detected in C. sinensis (free water > bound water > immobilized water). The internal water distribution and water content changed during drying process. The moisture changes were similar in hot air drying, drying after steaming, and drying in shade, the total water gradually decreased, and the combining degree between moisture and non-water components enhanced. Steaming promoted the water loss rate of C. sinensis slice, the water loss rate was higher in drying after steaming than in hot air drying, and the difference was significant (P < 0.05). During the intermittent drying, the conversion of different states of water would occur in order to return to a relatively stable equilibrium. During the low temperature drying process, immobilized water content decreased and free water content increased. The low-temperature drying has less damage to the tissue, which is more conducive to the conversion of immobilized water into free water, and thus the water dissipated faster. During the early of drying, high temperature caused tissue structure damage, the bonding force between water and non-aqueous tissue would be strengthened because of the tissue shrinkage. Conclusion The three different types water content and peak area in T2 was positively correlated. The LF-NMR technique would provide useful guides for the investigation of water distribution and variation of C. sinensis, which will provide a theoretical basis for C. sinensis processing.