Umami and koku: Essential roles in enhancing palatability of food

Abstract

“Umami” (or umami taste) and “koku” are Japanese words born and used for a long time in the characteristics of traditional Japanese cuisine, and both are related to deliciousness of food mainly on the basis of functions of glutamate. Although umami is now worldwidely accepted as a basic taste together with the four basic tastes, sweet, salty, sour, and bitter, it is needed to know the accurate functions of glutamate in terms of its taste, umami, and flavor-enhancing action. Umami, from its discovery to its receptor mechanisms, is described for a better understanding of its taste. The flavor-enhancing action is related to koku. Koku is a conceptual word used by the Japanese on a daily basis for foods and drinks, implying enhanced deliciousness accompanying “thickness,” “continuity,” and “mouthfullness” in flavors and textures. Koku could be induced by integration of odor, texture, and taste of complex ingredients in foods. Concerning only the taste aspect of koku, which is called “kokumi,” it is supposed that responses to umami substances are enhanced by certain substances (kokumi-inducing substances) contained in complex ingredients or added from outside. Kokumi substances are known to be agonists for calcium-sensing receptor (CaSR). Better and accurate knowledge on umami and koku is essential to understand the important roles of glutamate in inducing palatability of food.