Umami - the savoury taste

Umami as a taste was not proposed until 1908. However, there has been an appreciation of a savoury taste quality that is neither salty, sweet, bitter or sour for many years, and in many cultures. 

What is umami

In a nutshell umami is the taste of substances called glutamates and ribonucleic acids. To a lesser degree the amino acid aspartate is also involved. While taste receptors for sweetness detect sugar, those for umami detect glutamate and ribonucleic acids.

Glutamate - why taste it

Glutamate is one of twenty amino acids that make up proteins. It has been postulated that we get a positive sensation when eating glutamate containing foods in order to encourage us to eat protein. Protein is needed for growth, recovery and virtually all functions of our body.

A baby has a positive response to both sweet and umami tastes. This is to enable it to consume breast milk, which contains sweetness, in the form of the milk sugar lactose and umami in the form of free amino acids, the most common by far being glutamate(1).

Glutamate is part of the additive monosodium glutamate - MSG, that is used here in the UK, in Chinese food. See health considerations below.

Ribonucleic acids

Ribonucleic acids indirectly help us make our own proteins and fats and as such are also useful in our diet. They are also responsible for growth as they form the basis for the DNA that allows our body to grow and repair itself.

The two ribonucleic acids involved in umami taste are inosinate - IMP and guanylate - GMP.

One complements the other

Glutamate in conjunction with ribonucleotides gives a much stronger taste sensation than glutamate alone.

Which foods contain umami

Meat, fish and many vegetables contain the umami taste. The strength of the taste is modified by breaking down proteins and ribonucleotides prior to tasting them. As such slowly cooked meat and vegetables often contain more umami flavour than raw meat or vegetables. A good example is caremalised vegetables.

How do we taste umami

It has not been until very recently that scientists have detected taste receptors that can detect umami(2). There seem to be some that just detect glutamate, called mGluR1 and mGluR4. There are others that detect glutamate in conjunction with various ribonucleotides. These taste receptors are called TAS1R1 and TAS1R3(3). They combine to help us taste glutamate in combination with the nucleotide IMP. It is worth noting that it is likely that other receptors may be found in future as tests have shown animals have an ability to taste umami even without some of these taste receptors.

A common misconception is that tastes are localised into particular sections of the tongue. In fact taste buds are located on the tongue, in the soft palate (upper back part of the mouth), and in the throat. The different types of taste receptors are found on taste buds throughout the tongue and mouth.

Health considerations

MSG - monosodium glutamate, is a product developed by the original Japanese discoverers of umami taste. There is quite a debate about whether it is safe or not. The problem is that glutamate excites our nerve cells. Too much could cause problems. In particular some chronic health conditions may be linked with MSG, such as fibromyalgia and irritable bowel syndrome - IBS(4).

A search of the free medical research library "pub med" for MSG yields a number of articles looking at connections between MSG and various other health problems(5). These include headache for which there is some evidence, asthma for which evidence is limited and obesity for which evidence seems very strong. The reason for the link with obesity is most likely due to MSG increasing our appetite.

Which foods contain MSG

So the question follows: if you are suffering from these conditions, what foods and additives do you need to avoid(6).

Glutamate Content(mg/100g)    
Cow's Milk2Potatoes102Peas200
Human Milk22Corn130Grape juice258
Eggs23Oysters137Fresh tomato juice260
Beef33Tomatoes140Walnuts658
Fish (Mackerel)36Broccoli176Soy Sauce1090
Chicken44Mushrooms180Parmesan cheese1200
    Roquefort cheese1280

Equally there are some additives that contain MSG that you need to be aware of(7).

Autolyzed YeastCalcium CaseinateGelatin
GlutamateGlutamic AcidHydrolyzed Protein
Monopotassium GlutamateMonosodium Glutamate Sodium Caseinate
Textured ProteinYeast ExtractYeast Food
Yeast Nutrient  

DrDobbin says:

Umami taste is clearly something to enjoy and can help guide you towards some healthy foods. However, it seems likely that too much of one component of this taste, glutamate, may be bad for your health in excess.

If you suffer from IBS or fibromyaligia or get symptoms after eating Chinese food it is certainly worth being aware which foods and additives could affect you badly.

References

1) http://www.ncbi.nlm.nih.gov/pubmed/10963461

2) http://ajcn.nutrition.org/content/90/3/738S.abstract 

3) http://ajcn.nutrition.org/content/90/3/770S.short

4) http://www.drbriffa.com/2012/08/31/dietary-excitotoxins-linked-with-fibromyalgia-and-irritable-bowel-syndrome/

5) http://articles.mercola.com/sites/articles/archive/2009/04/21/msg-is-this-silent-killer-lurking-in-your-kitchen-cabinets.aspx

6) http://www.msgfacts.com/nutrition/what_foods_are_glutamate-rich.aspx

7) http://articles.mercola.com/sites/articles/archive/2009/04/21/msg-is-this-silent-killer-lurking-in-your-kitchen-cabinets.aspx