Date Published: April 18, 2014
Publisher: Public Library of Science
Author(s): Shizuko Satoh-Kuriwada, Misako Kawai, Masahiro Iikubo, Yuki Sekine-Hayakawa, Noriaki Shoji, Hisayuki Uneyama, Takashi Sasano, François Blachier.
There is a close relationship between perception of umami, which has become recognized as the fifth taste, and the human physical condition. We have developed a clinical test for umami taste sensitivity using a filter paper disc with a range of six monosodium glutamate (MSG) concentrations. We recruited 28 patients with taste disorders (45–78 years) and 184 controls with no taste disorders (102 young [18–25 years] and 82 older [65–89 years] participants). Filter paper discs (5 mm dia.) were soaked in aqueous MSG solutions (1, 5, 10, 50, 100 and 200 mM), then placed on three oral sites innervated by different taste nerves. The lowest concentration participants correctly identified was defined as the recognition threshold (RT) for MSG. This test showed good reproducibility for inter- and intra-observer variability. We concluded that: (1) The RT of healthy controls differed at measurement sites innervated by different taste nerves; that is, the RT of the anterior tongue was higher than that of either the posterior tongue or the soft palate in both young and older individuals. (2) No significant difference in RT was found between young adults and older individuals at any measurement site. (3) The RT of patients with taste disorders was higher before treatment than that of the healthy controls at any measurement site. (4) The RT after treatment in these patients improved to the same level as that of the healthy controls. (5) The cutoff values of RT, showing the highest diagnostic accuracy (true positives + true negatives), were 200 mM MSG for AT and 50 mM MSG for PT and SP. The diagnostic accuracy at these cutoff values was 0.92, 0.87 and 0.86 for AT, PT and SP, respectively. Consequently, this umami taste sensitivity test is useful for discriminating between normal and abnormal umami taste sensations.
Umami taste has become known as the fifth basic taste but, for the following reasons, is different from the other four basic tastes (sweet, salty, sour, bitter) , . In our taste clinic, some patients, especially older participants, have complained of a persistent subjective impairment of umami taste, although the other four basic taste sensations remained normal. This impairment sometimes remained even after clinical treatment had improved the other four basic taste sensations. Such patients often had complex problems including poor appetite and weight loss; observations consistent with previous findings indicating a close relationship between umami taste perception and physical condition in older people , .