A Second Helping Of Brussels Sprouts
In 1931, as he described in his paper, The Relationship between Chemical Constitution and Taste (Proceedings of the National Academy of Sciences (1932)), Arthur Fox, a scientist at Jackson Laboratories in Wilmington, was preparing a quantity of phenylthiocarbamide (PTC) when some dust escaped into the air. His colleague, Dr Noller, complained about its foul smell but Fox could not smell anything. The duo even tasted the crystals of PTC, Noller complaining of their extreme bitterness while to Fox they were tasteless.
Possessing a curious mind, Fox set out to discover why he and Noller differed so dramatically in their response to PTC. He tested what he described as “a large number” of people, discovering that the wildly differing reactions were common regardless of age, sex, and ethnicity, with most people falling into one of two categories: those who were able to taste the compound even at very low concentrations, whom he called “tasters”, and those who could not except in very high concentrations, “non tasters” or “taste blind”.
Intrigued by Fox’s findings, Albert Blakeslee extended the testing to examine the minimum concentration at which PTC can be detected, finding that people’s degree of sensitivity can vary by five orders of magnitude. Blakeslee and Fox also discovered that they could predict very accurately how sensitive an individual would be to PTC by analysing how other members of their family reacted to it. In other words, PTC sensitivity could well be hereditary.
As there was little or no understanding of our genetic make-up at the time, curiously, the potential hereditary link with PTC sensitivity was used to test paternity instead. The assumption was that if father and child had different reactions to PTC, they were unlikely to be related. Of course, it is not as simple as that as the sense of taste is subjective and can be weakened by other factors such as smoking, age, and diet, leading some to speculate just how many parents and children were wrongly matched because of their sensitivity to PTC.
By the 1970s, though, scientists had advanced sufficiently in their understanding of human genetics to have identified a specific taste gene, TAS2R38, of which we have two copies. Those who inherit the gene containing two copies of the variant, AVI, are not sensitive to the bitter tastes of certain chemicals, people with one copy of AVI and another, PAV perceive some bitterness in them, while those with two copies of PAV, sometimes known as “super-tasters”, find them exceptionally bitter.
Recent research has shown that those with the PAV form of the gene were two and a half times more likely to eschew vegetables than those without, reporting that they found broccoli, Brussels sprouts, and cabbages were especially and unpleasantly bitter. They were also prone to react negatively to dark chocolate, coffee, and even beer, although indifferent to salt, fat, or sugar.
Brussels sprouts do not contain PTC, but, like broccoli and cabbage, have compounds called glucosinolates which have a similar mix of nitrogen, sulphur, and carbon as that found in PTC. They form part of the plant’s defence mechanism to ward of pests and diseases, just as geneticists believe that the presence of PAV in the taste gene was vital in human evolution, allowing us to more easily detect foodstuffs that were harmful. Around 30% of us still have at least one copy of the PAV variant in our TAS2R38 gene.
Instead of an expression of fussiness, turning one’s nose up at the prospect of the sweet, nutty flavour of a well-cooked sprout might well be a pre-programmed genetic response. No such considerations worried Linus Urbanec. On November 26, 2008, the Swede broke the world record for eating the most sprouts in a minute, an incredible 31.
Thanks to my AVI variants, I am looking forward to my helping of Brussels sprouts on Christmas Day.
