We’re all aware of the four tastes – sweet, salty, bitter and sour – and many of us are also aware of the fifth, umami. But how many tastes are there, and how can understanding them help you to be healthier?
We’re very visual animals, so the idea of there being three primary colours, from which all others are derived, is very familiar – and the idea of finding a “new” colour is equally unimaginable. But our understanding of our sense of taste is so far behind that we are still discovering new ones – and the way they affect us is only just becoming clearer.
The fifth taste umami (from the Japanese for “pleasant savoury taste”) is often thought of as a quite contemporary discovery. In fact it dates back to 1908, and the isolation of MSG (monosodium glutamate) in seaweed. MSG has been in use ever since as a flavour enhancer, but its effect is now classed as taste in its own right. Previously the subject of scares about obesity MSG is in fact almost entirely digested in the gut. Contrary to popular belief MSG is also found in higher amounts in Italian meals than in Chinese.
A much more recent discovery is kokumi (literally “mouthfulness”), which imparts a density of flavour to the foods it appears in. However its status as a taste is in doubt because scientists were surprised to find that when eaten on its own it has no taste at all. Instead it imparts a thicker, more satisfying feel to the foods it appears in. This does open up uses in reduced and fat-free foods, where it can give them the same luxurious mouth feel as their full fat versions.
The fact that we are still discovering, and debating, new tastes is partly due to the way that taste receptors work. Firstly they aren’t just found on our tongues, and in our mouths. Taste receptors are also found in our lungs, where they respond to bitter tastes by relaxing the airways– it’s thought as an evolved adaptation to help fight infection. They’re also found throughout the intestines and pancreas, where they help to regulate our appetite and insulin levels. Taste receptors are even found in the testicles, where they influence sperm production based on the nutritional state of the body as a whole.
The complexity of taste receptors also extends to those found on the tongue. As well as telling us about the taste of the food they send messages direct to other parts of the gut without involving the brain. For instance when they detect sugar they prime the gut for action, and when they detect sensations such as sweet, umami, and kokumi they send “fullness” signals to the gut. This is being used to develop slimming aids which directly target those receptors in the mouth, naturally suppressing the appetite and leading to weight loss. Success here could lead to treatments for bariatric patients, and those with Prader-Willi Syndrome.
However these discoveries aren’t just about learning to suppress appetite. A quarter of those over 70 years old lose their sense of smell, and so lose their ability to taste. One common reaction to this is to increase salt intake, to try and recapture the sensation of taste, but bringing risks around hypertension and stroke. The other reaction is for people to see a loss of appetite, with the very real danger of malnutrition. Kokumi, which does not rely on smell, may be able to bring the sensation of satisfaction back to those who have lost the ability to taste, keeping them eating as normal.
The ability of kokumi to work when the sense of smell is reduced is also behind its potential application to a rather less medically pressing problem. The lower air pressure and oxygen levels on planes affect dull our sense of taste – it seems kokumi may offer the solution at last to endless complaints about airline meals.
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