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

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Changes in saltiness evaluated by sensory analysis, ²³Na nuclear magnetic resonance (NMR) signal and water activity (a_w) 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 a_w and the saltiness decreased with fermentation time. The saltiness correlated with the line width (p<0.001) and the a_w (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 a_w 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 a_w and the saltiness of miso during fermentation were caused by the increase in water-soluble substances such as glutamic acid.