快猫短视频

EVEN with a blue foam nose-clip cutting off my sense of smell, I know I鈥檓 eating something remarkable. I鈥檝e come to an ordinary-looking office at the University of London鈥檚 School of Advanced Study, where only a scattering of plates and cutlery hint at what I鈥檓 here for. When my host Jozef Youssef, of food science collaboration Kitchen Theory, places two dishes of risotto in front of me, he has actually forgotten which contains the mysterious ingredient I鈥檓 here to try. But to me the difference is unmistakable. One is zingy, salty, creamy. The other pales in comparison.

The secret behind the more delectable of the two dishes is the kokumi ingredients Youssef has spiked it with. Kokumi is a flavour concept originating in Japan that some foodies think could rank alongside the four familiar fundamental tastes, salt, sweet, bitter and sour. With many food flavours actually due to smell rather than taste, the fact that I experience kokumi鈥檚 potency with my nose disabled certainly suggests something special is going on.

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The discovery of kokumi is just one of many taste phenomena that have recently taken scientists by surprise. Our efforts to understand what constitutes taste have led us to realise how strange this sense really is. For one thing, it isn鈥檛 just confined to our mouths 鈥� it crops up in all sorts of unexpected corners of our bodies. It鈥檚 becoming clear that taste is about more than just pleasure. It is hardwired into our basic biology and we are just learning how to harness it.

When we eat something, what we experience is its flavour, a combination of taste, smell and other sensory inputs. But while the scent of food is derived from a palette of 10,000 volatile chemicals, taste is much simpler. Millennia of experience and centuries of data have identified those four fundamental tastes. These are the best known primary tastes, analogous to primary colours in that they can be combined to beautiful effect but not broken down further.

An early hint that the gamut of tastes might go further came in 1908 when a Japanese scientist extracted a compound called monosodium glutamate (MSG) from a tasty type of seaweed. Kikunae Ikeda of Tokyo鈥檚 Imperial University identified the molecule in his search for a new primary taste. He considered MSG the embodiment of what he called umami, which can be translated as 鈥渄elicious taste鈥�. People often describe it as the savoury quality of meats and cheese.

The following year, a company called Ajinomoto started selling MSG as a flavour enhancer. With Ajinomoto using umami as a central part of MSG鈥檚 branding, the idea that it is a primary taste has spread. Today, most of us consume MSG every day in our food (see 鈥�MSG in me鈥�).

Foodies across the world may now be familiar with umami, but whether it really is a primary taste has been debated for decades. That鈥檚 partly because there is no firm definition of what constitutes a primary taste. Instead, settling arguments like this involves painstakingly providing convincing evidence. One critical exercise is identifying receptors in our taste buds that recognise the specific taste molecules involved. Other important tests include conducting tastings with groups of people who don鈥檛 have the genetic instructions to make the receptor in question. If they can鈥檛 discern a taste, it鈥檚 probably a member of the primary club.

Attempts to find receptors for the assumed primary tastes were boosted in 2000 with the publication of the first draft of the human genome. By 2011, scientists 鈥� principally Charles Zuker鈥檚 team at Columbia University in New York 鈥� had used it to hunt down receptors for salt, sweet, sour, bitter and umami. That, combined with an abundance of tasting data, has convinced most people that there are five primary tastes.

While Ajinomoto must have been pleased to see umami make the grade, the firm isn鈥檛 resting on its laurels. Rather, its researchers are now working out how to use kokumi, an entirely different concept to umami.

The term kokumi, which roughly translates as 鈥渄ense, full-bodied flavour鈥�, was originally used to refer to a property of cooked garlic. In 1990, Ajinomoto researchers identified several compounds containing sulphur that they thought were responsible. But their taste tests showed up something strange. Although Ajinomoto has found a receptor for kokumi in taste buds, reported that they had no taste of their own. Instead, they gave food what the firm calls 鈥渃ontinuity, mouthfulness and thickness鈥�.

Ajinomoto hopes that kokumi could be a way of returning the thick, luxurious texture that foods can lose when fat is stripped out. In January, the firm showed in a taste test that adding a kokumi compound to a low-fat peanut butter made it seem thicker to people eating it (, vol 4, p 16).

Turn up the bass

Having tasted risottos and tomato sauces Youssef prepared with and without the rare and expensive kokumi ingredients, I can see how that might be possible. After the tasting, he reveals that the kokumi dishes have less salt than their blander counterparts. He highlights the potential health benefits of improving taste while reducing fat, salt and sugar levels. Yet he is also cautious, as we don鈥檛 yet know if there鈥檚 a limit to how much you can eat. 鈥淚t鈥檚 all well and good to say we can use less salt and add X, but we have to look into X as well,鈥� he says.

Love at first bite: kokumi could simulate a thick, fatty feel (Image: Bruce Davidson/Magnum Photos)

The receptor Ajinomto has found bodes well for kokumi鈥檚 primary status. Oddly though, this receptor was already known to exist in our bodies. Its main job is sensing calcium; detecting kokumi seems to be an evolutionary afterthought. Still, Sarah Brennan at Cardiff University in the UK, who studies the receptor, agrees that it seems to be involved in how the kokumi taste works. She points to a 2009 study that showed compounds known to strongly stimulate the receptor also increase the kokumi intensities people experience, while molecules that block the receptor suppress kokumi鈥檚 flavour enhancement .

While kokumi seemingly fulfils this critical prerequisite for being a primary taste, Brennan is not so sure. 鈥淐an you call something that has no taste a basic taste? I鈥檝e always equated it to the bassline in a piece of music. The lead instrument is already there, however the bassline gives a bigger, fuller sound.鈥� Ajinomoto researcher Motonaka Kuroda agrees that kokumi鈥檚 lack of taste means it can鈥檛 be a taste, and flavour isn鈥檛 the right term either. So what has been going on in my mouth?

Barry Smith at the University of London鈥檚 Centre for the Study of the Senses thinks the answer lies in a more subtle contributor to flavour: touch. We already know that touch is involved in flavour perception. For example, pain and temperature-sensing receptors connected to the trigeminal nerve, which is responsible for sensation in the face, can be irritated to give peppermint鈥檚 coolness and chilli or mustard鈥檚 heat. But because kokumi doesn鈥檛 result in a taste perception in itself, Smith thinks it must be acting in a different way, perhaps on the kind of touch receptors that respond as food flows around in the mouth. Even though this is the normal way we determine texture, it plays a complex role in flavour, for example, making creamier food seem sweeter than it really is.

A touch effect would explain why kokumi still works when my nose is pegged, and the unusual words like 鈥渕outhfulness鈥� used to describe it. It would also widen the potential uses for kokumi ingredients. A quarter of people over the age of 70 have no sense of smell, Smith says. Because of that 鈥渁 lot lose interest in eating and become malnourished鈥�, he says. 鈥淥thers reach for the salt, increasing their risk of stroke and heart disease. Maybe if we鈥檝e got this other way of enhancing flavour, that鈥檚 going to help them.鈥� Kokumi might also improve aeroplane food. One of the principal reasons it seems lousy is that our sense of smell is less effective at the lower air pressure found in cabins.

With kokumi out of the running, you might think we are back to just five primary tastes. Not so: Smith considers a sixth and seventh to have already been found. He says a metallic taste, like we get when sucking the blood from a cut, is the sixth, and . He points to strong evolutionary reasons, both for nutrition and self-preservation, for these seven. A bitter taste receptor would help us spot toxins in poisonous plants, for instance. A much longer list of primary tastes is unlikely, he says, because there are only a limited number of evolutionary drivers.

鈥淭aste receptors have been found in the lungs and 鈥� weirdly 鈥� the testicles鈥�

His comments allude to kokumi and several other primary taste candidates that have emerged (see: 鈥淔rontiers of taste鈥�, below). Yet Robert Margolskee, director and president of the Monell Chemical Senses Center in Philadelphia, Pennsylvania, is doubtful about going beyond five primary tastes. He doesn鈥檛 feel that data from tasting studies show whether fat is a primary taste or merely a modifier of others. He is confident, though, that there is a plausible candidate for a fat taste receptor 鈥� and that it is important in our gut as well as our mouth.

Margolskee knows this because he specialises in looking at similarities between cells in the gut and the taste cells in our mouths. That interest stems from the search for the sensor that triggers a rise in blood insulin when we eat glucose. In 2007, Margolskee and Josephine Egan at the US National Institutes of Health found taste receptors in cells in the first section of our small intestine that are involved in .

This discovery showed that taste receptors aren鈥檛 just for consciously testing food, they can send messages through our bodies without involving our brains. And they aren鈥檛 just in guts. Before the salt taste receptor was identified in taste buds in 2010, it had previously been found in cells from a cow鈥檚 neck. 快猫短视频s have also found taste receptors in organs such as the lungs and 鈥� weirdly 鈥� the testicles. What are they doing there? Margolskee speculates that they might be detecting nutritional status to avoid the body wasting valuable energy making sperm when food is scarce. But no one knows for sure.

Companies are already trying to exploit these discoveries. For example, San Diego based firm Ambra Biosciences is developing a dietary supplement called Lovidia that targets the sweet, umami and bitter receptors in the gut. The idea is to hit these receptors and get them to dispatch more fullness signals than normal, helping people feel satisfied for longer and so lose weight. Ambra鈥檚 chief executive Martin Brown says unpublished studies have shown significant differences in weight loss when people take the supplement compared with placebo. The exact ingredients in Lovidia are secret, but it should appear on US shelves in late 2015.

More opportunities like this look certain to emerge, given how rapidly our knowledge of taste is evolving. For instance, recent research has shown that . Some taste cells on the tongue release hormones into the bloodstream when they detect sugar, Margolskee says, instructing gut cells to prime for action. So the tongue isn鈥檛 only a sensory organ for our brain, it鈥檚 also the very beginning of the digestive tract. Just when I thought taste biology couldn鈥檛 weird me out any more, as well as tasting with my gut, I鈥檝e effectively got gut in my mouth 鈥� as do we all.

This article appeared in print under the headline 鈥淩efined taste鈥�