Soup stock samples were prepared using 3% Niboshi varying water-extracting time from 0 to 24 hr and boiling time from 1 to 120 min. Amount of 5′-IMP, 5′-AMP, lactic acid and phosphoric acid in the sample increased rapidly up to 10 min boiling or 2 hr extracting and increased slowly up to 30 min boiling or 6 hr extracting then leveled off.
The sensory test panel judged the soup stock of 30 min boiling more tasty and preferable than that of 1 min boiling. We added 5′-IMP, 5′-AMP and phosphoric acid to the soup stock of 1 min boiling so that the contents of that those of the soup stock and equal to of 30 min boiling. Addition of these components gave an increase in Umami taste and preference. However, added lactic acid was not effective to improve the taste or preference.