Kokumi, a Japanese word translated as "mouthfulness" or "heartiness", describes a widening and lengthening of flavours sensation in the mouth, it is a taste enhancer that brings a depth to the other tastes. The issue here is whether we are trying to describe a taste or a sensation.
When a soup or a stew has simmered for several hours, it takes on a richer, deeper flavor. And when cheese is allowed to mature, its flavor becomes more complex and lasting. What accounts for this form of enhanced deliciousness?
Kokumi was discovered in 1989 in the laboratories of Ajinomoto, the company originally founded by the umami pioneer Kikunae Ikeda. They began investigating what onions and garlic bring to so many flavorful dishes, something quite different from umami. While umami imparts savory flavor or meatiness, kokumi is a sense of richness, body and complexity that some compare to the way wines age and improve over time. Although kokumi substances have no taste of their own, they seem to make other foods taste and feel better, enhancing not only umami but also salty and sweet flavors.
The Ajinomoto Group’s research into kokumi substances in foods like garlic led to the isolation of a peptide, or chain of amino acids, called glutathione.
It was already suspected that the peptide glutathione activates calcium sensing receptors on the tongue that could be a basis of perception of kokumi, and that other amino acids and peptides might activate calcium receptors too, possibly more powerfully and efficiently than glutathione.
So kokumi is not a taste but enhance the characteristics when combined and with a lot of benefits: using kokumi substances as flavor modifiers enhances taste while reducing dietary fat, salt, and sugar.
Another benefit could be in stimulating appetite as we age. Older people show a tendency to lose their sense of smell and taste, leading to reduced food intake and poorer nutrition.