gingerol

The word entered the language in 1879, in brackets, in a methods paragraph. John Clough Thresh, a pharmaceutical chemist from Buxton, had a colleague exhaust twenty-eight pounds of Jamaica ginger with ether, spent weeks stripping the resins out of what came off, and described the pale, odourless, extremely pungent treacle that survived as the substance "which I have called gingerol." Working out what he actually had in the flask took another ninety years: Connell and Sutherland established in 1969 that gingerol is a family, and the bracketed number in [6]-gingerol counts the carbons in the tail that falls off when the molecule is cleaved.

[6]-gingerol is the abundant one, C₁₇H₂₆O₄, mass 294.4. It carries a hydroxyl group two carbons along from a ketone, and that arrangement is fragile: heat or acid eliminates a water molecule across those carbons to give [6]-shogaol, mass 276.4, and the difference between them is exactly one water. The reaction is pH dependent, most stable at pH 4, and reversible. Drying a rhizome in open sun left 13.48 milligrams of 6-gingerol per gram; hot air at 150 degrees cut that to 4.94 and raised 8-shogaol twelvefold. And shogaols are twice as pungent, so dried ginger is a hotter compound at a lower concentration.

The burn has a known address. Gingerols and shogaols are agonists at TRPV1, the receptor capsaicin works on, binding the same pocket in the same orientation, held by hydrogen bonds to the same two amino acids. Measured against the human channel, capsaicin's EC50 is 9.8 nanomolar, [6]-shogaol's 568 and [6]-gingerol's 2,399: a chilli's trick, about two hundred and fifty times more gently. In the gut the signal runs through a different channel, TRPA1. And after a 2 gram oral dose, free 6-gingerol was never detected in plasma at any point over twenty-four hours, in either of two studies; what appeared instead were its glucuronide and sulfate conjugates, with half-lives under two hours, and in the more sensitive follow-up a trace of free 10-gingerol and 6-shogaol. In this library it is the heat in fourteen teas, a curry and a smoothie, always traced to fresh ginger.