Changes in 23Na Nuclear Magnetic Resonance Signal, Water Activity and Saltiness of Miso during Fermentation

Changes in saltiness evaluated by sensory analysis, 23Na nuclear magnetic resonance (NMR) signal and water activity (aw) of miso during fermentation were investigated. The line width (full width at half maximum intensity) of the 23Na NMR signal of the miso extract increased with fermentation time, while the aw and the saltiness decreased with fermentation time. The saltiness correlated with the line width (p<0.001) and the aw (p<0.001). The line width was not much affected by NaCl concentration, but it increased on addition of glucose, casamino acid, ethanol and lactic acid. The line width of 23Na NMR and the aw of the miso model solution consisting of sodium chloride and these substances were not much changed during storage over 100 days. This suggests that the increase in the line width and the decreases in the aw and the saltiness of miso during fermentation were caused by the increase in water-soluble substances such as glutamic acid.