23Na-NMR Imaging of Foods.

Abstract

The sodium condition in foods as well as the water condition is an important factor controlling food quality. A 23Na-NMR imaging probe was devised for this investigation, and distributions and relaxation times of Na ions were measured using phantoms, containing various concentrations of Na ions with different mobilities. The images had a spatial resolution of 0.8×0.8 mm area and 8mm thickness (5.12mm3). The signal intensity obtained was proportional to the concentration of Na ions and it depended strongly on the mobility of the Na ions; Na ions with short relaxation times were difficult to detect because the echo-time for the measurements (36 msec) was comparable to the relaxation time of the Na nucleus. Distribution maps of Na ions in foods, such as a salt-pickled plum and a cucumber pickled with fermented soybean paste, were obtained. They provided different information from that of 1H-NMR images. Considering that the accumulation of sodium affects the taste and the texture of food materials, 23Na-NMR imaging may be useful for monitoring food quality in detail such as in the sub-tissue level during storage and processing.