Saturday, February 25, 2012

Super Tasters and Smells in Space

Back in Junior High School1, my first chemistry teacher ran a fascinating experiment. He dabbed a small amount of dilute capsaicin on the back of a piece of bread, and handed it to each class member. Of course, most of us felt the burn, but not one girl - she was genetically insensitive to capsaicin’s painful effects.

The science of taste and smell fascinate me, since they not only underlie many of our daily chemical interactions, but provide clear survival benefit to the species. The ability to smell smoke or taste bitter alkaloids might allow you to detect fires or avoid poisonous foods. In 2006, Glindemann and coworkers reported the source of the “iron smell,” the dark, musky odor produced when you touch coins or metal handles. His group traced the smell back not to compounds in the metal itself, but to chemical changes of body oils spontaneously produced upon contact (one of the stronger odorants, 1-octen-3-one, shown at left). The chemists theorize that the ability to smell these metallic odors traces far back in our evolutionary history, to when “blood smell” helped early human hunters track their prey through the woods.

Well, if smells are so critical, pity the poor astronauts. Space missions show that after a few days in weightless conditions, astronauts can no longer smell or taste their food properly, and begin to crave hot spices and bold flavors. NPR reporter Joe Palca explored this condition, called “stuffy-nose effect” or the “Charlie Brown syndrome” (due to the enlarged appearance of your head in space when your facial tissues swell with fluid, an effect of lessened gravity).

Charlie Brown and Snoopy
Source: The Telegraph | Charles M. Schultz
Want to help test the phenomenon? A joint Cornell /U.Hawaii study is now recruiting applicants. You’ll live in a simulated Mars mission habitat in Hawaii, where researchers will test food preparation with limited ingredients. They’ll induce the “stuffy-nose effect” with specialized beds that keep the head slightly lower than the rest of the body, and test various spices and food replacements for space palatability.

Maybe these scientists shouldn’t worry about smell deprivation, and just recruit a bunch of supertasters. These genetically gifted sense superstars possess more taste buds (papillae) on the tongue surface than others, which can be observed by simply staining the tongue blue and looking in a mirror. Supertasters report heightened sensitivity to subtle changes in food or drink, and naturally cluster in occupations such as chefs or sommeliers.

Count the taste buds!
Source: NPR | Maggie Starbard
The physiological prowess of supertasters was first noted in back-to-back PNAS papers in the 1930s. Amazingly, the trend started when two chemists – Drs. Fox and Noller, of DuPont – exhibited markedly different reactions to the taste of phenyl thiocarbamide dust in the air. The two scientists then prepared several analogues of the parent thiocarbamide, and ran around asking people to taste them!

The second paper, from geneticist Albert Blakeslee at the Carnegie Institution in Cold Spring Harbor, tested the effect of dilution on the taste sensations of a few hundred people of different racial and ethnic backgrounds. On the menu, in addition to the DuPont compound, were hydrochloric acid, picric acid, salt, and saccharine. Blakeslee found that there were distinct groups of people who could taste at certain thresholds, the “tasters” and the “non-tasters.” Further research, as explained by food scientist John Hayes in a broadcast of the WNPR Colin McEnroe show a few nights back, has shown that humans actually fit into three distinct categories: “non-tasters,” “medium-tasters,” and “supertasters.” The updated test involves placing a small crystal of propylthiouracil (PTU, see above) on the tongue and recording the intensity of the each person’s reaction; supertasters recoil at the bitterness, while “non-tasters” barely notice a difference.

1.No, it wasn’t ‘middle school’ back then, and yes, I walked uphill both ways, in the snow, carrying my books.

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