Ask most people how many tastes we humans can identify and they’ll probably tell you five – sweet, sour, salty, bitter, and umami. The first four have been around for a long time, with the Ancient Greek philosopher Democritus describing the last of them, bitter, 2.5 thousand years ago. Umami, on the other hand, was only "discovered" in 1908. Even then, it wasn’t scientifically recognized and umami (meaning “delicious” or “yummy” in Japanese) did not become “official” until 2002.
Now, according to new research from scientists at the University of UC Santa Barbara (UCSB) and Korea, there may be a sixth to add to the list – calcium.
So, what does calcium taste like? Apparently, humans describe it as being slightly bitter and sour. You might want to think about foods that are high in calcium like milk (or anything else dairy), kale, and sardines.
The important thing to know about calcium is that too much or too little of the stuff can be dangerous. This means that being able to sense (read: taste) calcium could be essential for our survival.
For their research, published in the science journal Neuron, the team used vinegar flies – an organism that (like humans) can taste calcium. These flies (again, just like humans) need an optimal amount of calcium to survive. Yet while they tend to reject to foods high in calcium, they seem surprisingly ambivalent towards foods low in calcium.
“It turns out that fruit flies don’t have a mechanism for sensing low calcium even though it’s good for them, but they are trying to guard against consuming too much calcium,” senior author Craig Montell, from UCSB’s Molecular, Cellular, and Developmental Biology and Neuroscience department, said in a statement.
The scientists identified three taste neurons called gustatory receptor neurons (GRNs) needed to sense calcium, then proceeded to remove one of these from some of the flies. When exposed to a petri dish containing sugar on one side and a sugar-calcium mix, the mutant flies could not distinguish between the two to the point that they consumed too much calcium, developed health problems and, ultimately, died. Flies that had not undergone the neuron removal, meanwhile, purposefully avoided the high-calcium side of the dish.
“Surprisingly, we found that calcium avoidance occurred through two mechanisms: activation of a unique class of GRNs, distinct from those that sense bitter compounds and which cause a stop-feeding signal when activated. In addition, calcium inhibits sugar-activated GRNs,” explained Montell.
“In humans, high calcium is associated with many diseases and can even be life threatening. Our results suggest that calcium taste might function primarily as a deterrent in wide range of animals, including humans,” he added.