The flavor-enhancing action of glutamate and its mechanism involving the notion of kokumi

Abstract

The sodium salt of glutamic acid, or monosodium glutamate (MSG), has two effects in foods: one is to induce a unique taste called umami, which is one of the five basic tastes, and the other is to make food palatable (i.e., flavor-enhancing or seasoning effects). However, the mechanism behind how MSG makes food more palatable remains poorly understood, although many food scientists seem to believe that the umami taste itself plays an important role. Here, we propose an alternative notion regarding this topic based on previous and recent studies. When added to complex food compositions, MSG facilitates the binding of existing kokumi substances to kokumi receptors. In turn, these bound kokumi substances enhance the intensity of umami, sweet, salty, and fatty tastes, resulting in increased palatability accompanied by kokumi flavor, such as thickness, mouthfulness, and continuity. The requisite for sufficient palatability and kokumi flavor is a good balance of umami and kokumi substances. This framework gives a scientifically useful background for providing newly developed foods, including cultured meat and plant-based meat substitutes, with good taste characteristics.

Fig. 1. A theoretical representation of kokumi with six related characteristics.

Under the influence of kokumi substances, food with umami and other taste substances (A) becomes more palatable with the kokumi attributes (B). This image corresponds to stages C and D in Fig. 2.

Fig. 2. A theoretical representation of the mechanism underlying how the addition of monosodium glutamate (MSG) induces kokumi and palatability in food containing kokumi and basic taste substances.

When MSG is added to food ingredients (A), the amount of MSG is increased (B). Increased MSG facilitates the binding of kokumi substances to kokumi receptors (C). The bound kokumi substances facilitate the binding of sweet, salty, and fatty substances to their corresponding receptors and enhances those tastes (D). Enhanced umami induces mouthfulness and continuity of sensation. Thickness comes from enhanced perception of the four tastes, and palatability is also induced on the basis of these palatable tastes (E).