2019-05-07 09:49:58
Veronique Greenwood
Kikunae Ikeda had been thinking a lot about soup.
The Japanese chemist had been studying a broth made from seaweed and dried fish
flakes, called dashi. Dashi has a very specific flavour warm, tasty, savoury
and through laborious, lengthy separations in a chemistry lab, Ikeda had been
trying to isolate the molecules behind its distinctive taste. He felt sure that
there was some connection between a molecule s shape and the flavor perception
it produced in humans.
But as it was just a few years past the turn of the 19th Century, there was not
yet a great deal of evidence to support the idea.
Eventually, Ikeda did manage to isolate an important taste molecule from the
seaweed in dashi: the amino acid glutamate, a key building block of proteins.
In a 1909 paper, the Tokyo Imperial University professor suggested that the
savoury sensation triggered by glutamate should be one of the basic tastes that
give something flavour, on a par with sweet, sour, bitter, and salt. He called
it umami , riffing on a Japanese word meaning delicious .
It cannot be said that at the time his idea was met with thunderous applause
from colleagues around the globe. For one thing, Ikeda s paper remained in
Japanese (it was eventually translated into English in 2002). Also, umami taste
behaves a bit differently from the others. It does not get stronger linearly
with higher levels of glutamate and other substances that trigger it, the way
that sweetness does.
The two are completely different types of tastes, Ikeda notes in his paper.
If these substances can be likened to color, umami would be yellow and
sweetness red. It was not exactly your standard scientific fare.
But more than a hundred years later, scientists around the world now
acknowledge that umami is real, and just as much a basic taste as the others.
It s not just found in seaweed: we get a hit of umami from tomatoes, meat,
broths, cheeses, and many other foods. How did this enigmatic yet brash taste,
hidden in plain sight for so many years, finally achieve recognition?
Over the decades, scientists began to put together how umami works. Each new
insight brought the claim put forth by Ikeda into better focus. For instance,
researchers identified two other molecules that could trigger the sensation:
inosinate, behind the umami of bonito fish flakes, and guanylate, behind the
umami of dried shitake mushrooms.
Looking closer at nerves sending messages from the mouth to the brain when
umami was tasted suggested that it and salt were operating via different
channels
And interestingly, the effect of having two of these molecules in the same dish
is synergistic. You get way more umami from a broth containing both bonito
flakes (inosinate) and seaweed (glutamate) than you get from either alone. You
get a similar effect from cooking beef (inosinate) with tomatoes (glutamate).
Some people suggested that perhaps umami was just a kind of saltiness. After
all, it often occurred in concert with that sensation. But taking away an
umami-triggering substance really did dramatically change perception,
researchers found. Looking closer at the nerves sending messages from the mouth
to the brain suggested that umami and salt were operating via different
channels.
A great deal of the recognition for Ikeda s insights probably came from the
discovery, about 20 years ago, that there are specific receptors in taste buds
that pick up on amino acids. Multiple research groups have now reported on
these receptors, which are tuned to specifically stick onto glutamate and the
other umami molecules that create synergistic effects.
In a way, it isn t surprising that our bodies evolved a way to sense the
presence of amino acids, since they are crucial for our survival. Breast milk
has about the same levels of glutamate as the dashi broth studied by Ikeda, so
we are probably quite familiar with the taste before we can even walk.
Ikeda, for his part, found a seasoning manufacturer and started to produce his
own line of umami seasoning. I believe that the time has come to revolutionise
the production method of this important seasoning, he wrote at the end of his
1909 paper, in hopes that better-tasting food would improve people s nutrition.
The product, a monosodium glutamate (MSG) powder called Aji-No-Moto, is still
made today. (Although rumours have swirled periodically that eating too mush
MSG can give people headaches and other health problems, the US Food and Drug
Administration has found no evidence for such claims. It just makes food taste
more savoury.)
Can something be a basic taste if we don t really taste it, per se?
The story of umami might make you wonder, are there other basic tastes out
there that we just haven t gotten around to noticing? Some researchers believe
we may have a sixth basic taste for fat. There are some good candidates for fat
receptors in the tongue, and it is clear that the body responds strongly to fat
s presence in food.
However, by the time fat levels are high enough that we can actually taste them
consciously, we tend not to like the flavour very much. So the question
becomes, can something be a basic taste if we don t really taste it, per se?
How much of taste is about encouraging or discouraging us to eat something, and
how much of it is the body, unbeknownst to us, keeping track of what s coming
down the chute?
Further deepening the mystery of flavour, Japanese scientists have introduced
the idea of kokumi to the wider world. Kokumi means a taste that cannot be
expressed by the five basic tastes, and also includes marginal tastes of the
basic tastes, such as thickness, growth (or mouthfullness), continuity, and
harmony, reads the site of the Umami Information Center (UIC), a group for the
promotion of umami research. Triggered by a trio of linked amino acids, the
kokumi sensation adds to the pleasure of certain kinds of foods, most of them
savoury.
Harold McGee, the food writer, had a chance to try some kokumi-inducing
preparations of tomato sauce and cheese-flavoured potato chips at the 2008
Umami Summit in San Francisco under the auspices of the UIC. He wrote, in terms
that pique the imagination of anyone curious about new taste sensations:
The flavours seemed amplified and balanced, as if the volume control and had
been turned up and an equaliser turned on. They also seemed somehow to cling to
my mouth a tactile feeling and to last longer before fading away.