The important role of umami taste in oral and overall health

Enjoyment of taste should be one of the greatest pleasures in human life. However,
aging is sometimes associated with decreased taste sensitivity. Loss of adequate gustatory
function may induce a poor appetite, reduced dietary intake, and weight loss, particularly
in the elderly 1]. In Japan, gustatory function is generally assessed using the filter paper disk test,
in which a filter paper soaked with a taste-inducing chemical solution is placed on
specific areas of the tongue and oral cavity. However, this test only assesses four
of the five basic tastes: sweet, salty, sour, and bitter. Because the taste quality
of umami, which is recognized as a fifth taste category 2-4], is not clinically assessed at present, information about umami taste disorders has
yet to be accumulated. We recently reported the specific loss of the umami taste sensation
with preservation of the other four taste sensations in some elderly patients 5,6]. The patients with loss of umami taste sensation also exhibited poor general health.
In this article, we first review our studies, including that of our newly developed
umami taste sensitivity test, and related studies concerning taste disorders with
particular focus on umami taste disorders and overall health. Second, we examine the
link between taste disorders and salivary flow because saliva assists and influences
the detection of taste by allowing diffusion of the taste substances to the taste
receptors, facilitating chemical interactions with food substances, and protecting
the taste buds 7]. Finally, we discuss clinical application of taste stimulation as a remedy for dry
mouth-related dysgeusia based on the gustatory–salivary reflex.