1H-NMR method enables early identification of degeneration in the quality of sweet potato tubers

In sweet potato tuber, which is a tropical plant, long-term storage leads to loss of water and carbohydrate, thus water mobility was investigated using H-1-NMR spectroscopy. Electrolyte leakage indicated that tubers stored at 15 degreesC for 1 year were partly injured and that frozen-thawed tissues were dead. Nuclear magnetic resonance (NMR) spin-lattice relaxation time (T-1) and spin-spin relaxation time (T-2) clearly increased with the duration of storage, whereas these values decreased in the dead tissues. Furthermore, Arrhenius plots for T-1 and T-2 were determined at temperatures ranging from 20 to 0 degreesC in 2.5 degreesC steps. In the fresh tubers, a strong converse temperature dependency was shown in the T-2 measurement. On the contrary, there was no temperature dependency in the T-2 of the dead tissues. Thus, the existence of inverse temperature dependency reflected tissue viability. Additionally, any change in the T-2 of the fresh tubers occurred at about 14 degreesC, which virtually coincided with the storage temperature of 15 degreesC. The slope change in T-2 might have responded to a physiological change as a primary event. In conclusion, monitoring water status by NMR could provide early identification of changes in the quality of post-harvest crops; this method shows great promise for use in environmental-stressed crop yield research.