Magnificent molecules
Phillip Broadwith, Chemistry World features editor highlights one of his favourite molecules.
In this issue: glutamate
When you eat a rich tomato sauce, or a
hearty soup or stew, what makes it taste the
way that it does? Is it slightly salty? Is there
a hint of sweetness from the perfectly ripe
tomatoes? A tang of citrus sourness or a note
of herbal bitterness to add depth, perhaps?
All of these things might be present, but the
overwhelming taste of such a dish is usually a
luxurious, mouthwatering savouriness, which
accentuates the impact of all the aromatic
flavour compounds that are filling your nose
at the same time as your tongue revels in its
taste sensation.
But where does that savoury taste come
from? Traditionally in western cuisine, it was
thought that the tastebuds on our tongues
could distinguish four different tastes –
sweet, sour, bitter and salt. But in 1908, the
Japanese chemist Kikunae Ikeda identified a
fifth basic taste, which he called umami, from
the Japanese for ‘delicious taste’.
Ikeda noticed that the taste of many foods –
particularly kombu dashi, a seaweed broth
popular in Japan – didn’t really fit into the
sweet, sour, bitter, salt categorisation.
Eventually he discovered the molecule
that was responsible for the seaweed’s
palatability – glutamate.
Certain foods are naturally high in
glutamate, such as tomatoes, mushrooms,
cured meats, fish and cheeses like Italian
parmesan or French roquefort. But it is
particularly enriched when these foods are
cooked slowly for a long time or fermented.
This is why stocks and broths, or soy
sauce and tomato ketchup are particularly
intensely flavoursome. Ingredients such as
Asian fish sauces or the quintessentially
British Worcestershire sauce and Marmite
yeast extract have especially high levels of
glutamate. And even the ancient Romans
reportedly used a fermented fish sauce
called garum to season food and enhance
its flavour.
The MSG debate
The sodium salt of glutamic acid is called
monosodium glutamate, or MSG. It was
developed as a food additive and flavour
enhancer following Ikeda’s discovery, and
quickly gained popularity as a cheap way to
boost the flavour of food made with lower
quality ingredients.
Takeaway Chinese food in the UK and US
gained a particular reputation for using MSG
to enhance flavour. In fact, pretty much any
processed fast food is likely to contain added
MSG, unless it specifically says otherwise.
But is it bad for you? Glutamate is a natural
component of proteins, and there is
chemically no difference between ‘natural’
glutamate and that added in the form of
industrially produced MSG. There have been
various arguments that MSG is bad for us,
even the suggestion of a medical condition
called ‘chinese restaurant syndrome’ or
‘MSG symptom complex’ caused by eating
too much MSG. But the medical evidence is
unconvincing. Like any chemical, if you eat
large enough amounts, it is not likely to do
you much good, but at the levels even the
most junk-food-hungry among us are likely to
ingest, there is no indication of health risks.
So the next time you are in a restaurant,
whether you’re grabbing a cheeseburger
or sitting down to a sumptuous ten
course Michelin-starred tasting menu,
take a moment to savour the taste. That
indescribable savouriness that leaves your
mouth watering and your tastebuds begging
for more. That’s the umami tingle that
comes from glutamate – be it from the finest
culinary ingredients or straight out of the
bottle marked MSG.
Originally published as part of Chemistry World’s
‘Chemistry in its element’ podcast series at:
www.chemistryworld.org/compounds
Deliciousness
Glutamic acid is one of the twenty standard
amino acids that make up proteins. Its
systematic name is 2-aminopentanedioic
acid – a five carbon chain with a carboxylic
acid group at either end and an amine (NH2)
group attached to the carbon adjacent to one
of the acids.
When glutamic acid is incorporated into
proteins, the side chain that sticks out from
the protein backbone is a short three-carbon
chain ending in a carboxylic acid. But under
the conditions in our mouths, one of the
acid groups is normally ionised to make a
glutamate anion, and it is this that binds to
umami taste receptors on our tongues to
produce that delicious savoury sensation.
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