Sunday, 26 August 2012

A Question of Taste

We think in discreet of discreet senses; taste, touch, sight, smell and hearing.  In complex biological systems like ourselves it is slightly more complicated.  Smell and taste are closely linked as anyone who has had a heavy cold and blocked sinuses can atest to; food can taste pretty bland.  In fact it appears that touch sensitivity is also linked to hearing!  Audio tests also show that those with good hearing were more likely to have sensitive touch (and touch is the principle by which percussionist Evelyn Glennie manages to overcome profound deafness).

I was listening to a pod cast featuring Jan Melichar, a psychiatrist at the University of Bristol, discussing how apples and onions trigger the same taste receptors in the mouth - and without the sense of smell, it is very difficult to differentiate between the two (save for some idea of the slighlty differing texture between the two).  Complex relations between the senses don't end there. 

Taste also ties up with mood and mental health or rather serotonin and noradrenaline - linked to the control and regulation of mood - can enhance our sense of taste.  This caught my attention because we often hear people saying they eat when they are bored (comfort/emotional eating). 

Melichar has performed some research showing that a smiple taste test can show which antidepressant, serotonin and noradrenaline affecting, will work best.

Taste also reflects anxiety levels.  In fact Dr Lucy Donaldson, co researcher with Jan Melichar, suggested that other messenger chemicals in the brain could be probed by studying our sense of smell. 

All this talk of taste and chemistry leads me on to a great book called The Disappearing Spoon by Sam Kean in which he gives a chemist's eye of how our senses are linked.  A little except to whet the appetite:
  • "Still more advanced than our unconcious immune system is our sensory equipment - our touch and taste and smell - bridges between our physical bodies and our incorporate minds. But it should be obvious by now that new levels of sophistication introduce new and unexpected vulnerabilities into any living system."

    "We trust our senses for true information about the world and for protection from danger, and learning how gullible our senses really are is humbling and a little frightening."
I've never really got on with chemistry (it is, after all, sociology for atoms), but Kean does a great job in making this stuff quite readable.  Having laid out the importance and fragility of our sensory system, it is onwards in to the detail:
  • "Alarm receptors inside your mouth will tell you to drop a spoonful of soup before it burns your tongue,but, oddly, chilli peppers in salsa contain a chemical, capsaicin, that irritates these receptors, too.

    Peppermint cools your mouth because minty methanol seizes up cold receptors, leaving you shivering as if an arctic blast just blew through. Elements pull similar tricks with smell and taste. If someone spills the tiniest bit of tellurium on himself, he will reek like pungent garlic for weeks, and people will know he's been in a room for hours afterwards.

    Even more baffling, beryllium, element four. tastes like sugar. More than any other nutrient, humans need quick energy from sugar to live, and after millenia of hunting for sustenance in the wild, you'd think we'd have pretty sophisticated equipment to detect sugar. Yet beryllium - a pale, hard-to-melt, insoluble metal with small atoms that look nothing like ringed sugar molecules - lights up taste buds just the same..."

    "This disguise might be merely amusing, except that beryllium, although sweet in minute doses, scales up very quickly to toxic. By some estimates, up to one tenth of the human population is hyper susceptible to something called acute beryllium disease, the periodic table equivalent of a peanut allergy. Even for the rest of us, exposure to beryllium powder can scar the lungs with the same chemical pneumonitis that inhaling fine silica causes....

    Now, some of the five types of taste buds are admittedly reliable. The taste buds for bitter scour food, especially plants, for poisonous nitrogen chemicals , like the cyanide in apple seeds. The taste buds for savoury, or umami, lock on to glutamate, the G in MSG. As an amino acid, glutamate helps build proteins, so these taste buds alert you to protein-rich foods. But the taste buds for sweet and sour are easy to fleece. Beryllium tricks them, as does a special protein in the berries of some species of plants. Aptly named miraculin, this protein strips out the unpleasant sourness in foods without altering the overtones of their taste, so that apple cider vinegar tastes like apple cider vinegar, or Tabasco sauce like marinara. Miraculin does this both by muting the taste buds for sour and by bonding to the taste buds for sweet and putting them on hair-trigger alert for stray hydrogen ions (H+) that acids produce...."

    "The taste buds for salty also are affected by the flow of charges, but only the charges on certain elements. Sodium triggers salty reflex on our tongues most strongly, but potassium, sodium's chemical cousin, free rides on top and tastes salty, too. Both elements exist as charged ions in nature, and it's mostly that charge, not the sodium or potassium pers se, that the tongue detects. We evolved this taste because potassium and sodium ions help nerve cells send signals and muscles contract, so we'd literally be brain-dead and our hearts would stop without the charge they supply."
This gives a vague insight in to how might a chemist be able to manipulate our response to commercial foodstuffs.  Real food anyone?

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