Since the dawn of time, we've had to take the bitter with the sweet. Now we may have to take the MSG with it as well.
For decades, researchers have been on the trail of the elusive fifth taste. Salty, bitter, sour and sweet are all accepted. But there has always been a belief that a fifth taste -- called "umami" by scientists but known more familiarly as the flavor enhancer monosodium glutamate, MSG -- deserved to be put in the same class. Now, scientists at the University of Miami School of Medicine have found evidence that it does -- and the ramifications of this may ripple across the culinary world.
The report delves into the little-known world of taste. Scientists have long searched for the receptors, the molecules on the surface of the tongue that give us the perception of taste through an interaction with the food. Reporting in the journal Nature Neuroscience, molecular biologist Nirupa Chaudhari and her colleagues have demonstrated that a modified form of a brain glutamate, mGluR4, is a taste receptor for umami. It's the first time a taste receptor has been identified.
"This is a milestone," says Ding Ming, a research manager for Novartis Consumer Health who has published studies on the subject. "If you know the receptor, and you know how to manipulate the receptor, you can make food taste better ... Hopefully, they will identify the sweet and the bitter receptors next using the same strategy."
Working with the tongues of rats, the researchers found that umami's receptor, a molecule, was truncated, with the front part of it missing. The researchers believe that if it wasn't shortened, the umami taste would be too intense.
Umami has for years has been on the brink of being accepted into the small cache of primary tastes. But it has been faced with resistance from the parts of the scientific community. Umami is a salt, but has also been known to trigger a sweet taste, leading to accusations that it doesn't have its own identity. Discovering its receptor will probably push it toward official recognition as the fifth taste.
"We're not trying to prove this, but I'm sure that umami now will become more recognized in the Western world and as an independent taste quality," says Stephen Roper, Ph.D., a Miami professor of physiology and biophysics, who worked with Chaudhari on the study.
Roper acknowledges that it's difficult to describe umami. Most Americans don't recognize it when they eat it. Parmesan cheese, for example, has a very distinctive umami taste. Protein-rich foods like steak, seafood, aged cheeses, mushrooms and tomato juice, among other things, have an umami component to them, though it is generally mixed in with other tastes as well.
Ming, Roper and others in this budding field think this study will have implications beyond the recognition of umami. "This umami taste probably drives our appetite for protein, just as sweet drives your appetite for carbohydrates and saltiness drives our appetite for salt or minerals," Roper says. "The bottom line is that glutamate tastes good and makes you want to eat. That's why adding monosodium glutamate makes food taste better and makes you want to eat more."
If adding glutamate to food does drive a person's taste for protein, researchers suggest, then it could possibly help those with nutritional deficiencies. The identification of the taste receptor means that food might possibly be manipulated to taste better. For example, foods high in nutritional value, like broccoli, would be more appealing to the palate.
"That would be interesting to do for the elderly and the hospitalized and the malnourished, where we feel that not only have they lost their food sensitivity, but also they might have a low protein intake and tend to eat carbohydrates," says Jo Ann Hattner, a clinical nutritionist and spokeswoman for the American Dietetics Association.
Until then, the search is on for the other receptors. What a bittersweet journey it will be.