
17 Feb 2015 Kokumi: is this the new umami?
The classical gustatory quartet of sour, sweet, salty and bitter was joined by umami not so long ago, and is now universally acknowledged as the fifth taste. More research has recently asserted that fat is the sixth taste – and now Japanese scientists have published new studies looking to the possibilities of kokumi as a new taste.
Umami, imparted by glutamic acid, a type of amino acid, and most commonly associated with a derivative of that chemical called monosodium glutamate (MSG), was identified in 1908 by Kikunae Ikeda, a chemist at what was then Tokyo Imperial University (now called the University of Tokyo). Ikeda wanted to pin down an ineffable taste he identified in dashi, a soup stock made from tuna and seaweed. When he found glutamates were the cause, he gave their effect a name compounded from the characters for “delicious” and “taste”.
Kokumi, similarly compounded from “rich” and “taste”, has been the subject of scientific inquiry in Japan since the 1980s, but is less familiar in the West. It is as much a feeling as a taste, and is described variously as “mouthfulness”, “thickness” and “heartiness”. Garlic, onions and scallops are all said to possess it.
But, though the source of kokumi is suspected to be a group of chemicals called gamma-glutamyl peptides, the search continues for special receptor-cells on the tongue, or anywhere else, that are tailored to detect these and thus create the sensation of kokumi.
That has led to scepticism about whether kokumi is a real physiological phenomenon. In this, it is much like umami was in the early days. Ikeda’s ideas were also disputed by sceptical scientists, until the discovery of glutamate receptors both on the tongue and in the gut. Such scepticism did not stop umami being commercially successful, though. Ajinomoto, a firm founded in 1909 to make and sell MSG, is now a huge flavourings business.
New research into umami and kokumi
Recently a set of papers in Flavour scientific journal outlines the frontiers of umami and kokumi research. One of them1, by Takashi Sasano of Tohoku University and his colleagues, suggests a link between loss of sensitivity to umami in the elderly and poor overall nutrition.
Dr Sasano supplemented the diets of his volunteers with kombucha, an umami-rich infusion of kelp. He noticed improvements in their salivation and appetite, and eventually in their weight and overall health. This supports the idea, promulgated by some researchers, that umami can stimulate a healthy appetite. Other studies, though, suggest the opposite—that umami signals satiation and helps curb overeating. And both could indeed be true, just as a little salt is attractive but a lot is repulsive. Moreover, if umami does signal satiation, then it might be a useful tool for dieticians.
Some people think kokumi might be deployed similarly, in order to reduce fat intake. And that suggestion is supported by two other papers in Flavour, written by Motonaka Kuroda and his colleagues. Dr Kuroda works for Ajinomoto, which is hoping to repeat with kokumi the success it had with umami. He and his team have been trying to find out how gamma-glutamyl peptides affect the taste of foods to which they are added.
A gamma-glutamyl peptide is a chain of three linked amino acids, with glutamate at one end of it. Dr Kuroda’s team added a variant of this theme called gamma-glutamyl-valyl-glycine to chicken consommé2 and low-fat peanut butter3. Taste-testers said the peptide-loaded version of the consommé had more “mouthfulness”, stronger umami flavour and was more mouth-coating. Low-fat peanut butter dosed with the peptide rated higher than the undosed version on measures of oiliness, thickness and aftertaste. The team therefore suggest that a dash of this peptide might be used to make low-fat foods more palatable, just as MSG is employed to increase the palatability of low-salt foodstuffs.
Flavoursome stuff
Whether gamma-glutamyl peptides really are the new MSG remains to be seen. Ajinomoto’s past work has shown that foods described as possessing kokumi contain them, and adding them to other foods seems to make for richer flavours. Dr Kuroda’s work, and studies like it, do not, though, prove that kokumi actually is a sixth taste. In some tests, kokumi effects seem to amplify umami sensations and in others the reverse is true. Ole Mouritsen of the University of Southern Denmark, author of yet another paper4 in Flavour, says that umami and kokumi may simply be two sides of the same biomolecular coin.
As ever, more research is needed. And more is coming—not least because this kind of thing has, for a century, been Ajinomoto’s bread and peanut butter, as it were. Whether kokumi really is a sixth fundamental taste has still to be determined. And it would be easy to be cynical and wonder how much that determination will be a branding exercise rather than a scientific one. But the history of umami, now universally recognised as a fifth fundamental taste, shows that the cynics are sometimes wrong.
Source: The Economist
- Journal reference: http://www.flavourjournal.com/content/4/1/10
- Journal reference: http://www.flavourjournal.com/content/4/1/17
- Journal reference: http://www.flavourjournal.com/content/4/1/16
- Journal reference: http://www.flavourjournal.com/content/4/1/18