Validation of preferred salt concentration in soup based on a randomized blinded experiment in multiple regions in Japan—influence of umami (L-glutamate) on saltiness and palatability of low-salt solutions

Sodium reduction is an important public health goal. Individual and population approaches are necessary for reducing the sodium content of processed foods and meals. The aim of the present study is to affirm the effect of monosodium L-glutamate (MSG), an umami substance, on the saltiness or palatability of low-salt solutions and to explore the preferred salt concentration in soup. Five hundred and eighty-four healthy participants from nineteen regions in Japan tasted 0.3, 0.6, and 0.9% NaCl solutions with or without 0.3% MSG. Evaluations of saltiness and palatability for each solution were conducted using a visual analog scale in a double-blinded randomized manner. Saltiness gradually increased depending on the concentration of NaCl. The saltiness of the 0.3% NaCl solution with MSG was rated significantly higher than that without MSG. The palatability ratings were higher for the solutions with MSG than for those without MSG for all NaCl concentrations. In particular, the palatability rating of the 0.3% NaCl solution with MSG was twice as high as that without MSG and was significantly higher than that of the other five test solutions. Furthermore, these results were observed to be approximately the same, irrespective of sex, age, region, etc. Salt reduction is believed to result in a loss of palatability. However, our results suggest that umami can compensate for the loss of palatability caused by salt reduction and that the addition of an appropriate amount of an umami substance can facilitate salt reduction from 0.9 to 0.3% without sacrificing palatability.