If you try to maintain your composure when eating a lime or a lemon without accompanying it with some other food, it will be difficult for the features of your face to remain rigid. Humans have the ability to react automatically when an acid or sour taste ends in our tongue. But why? How can a food smaller than a fist have such a strong effect on your body against your will?
There is no definitive answer to this, but there is a possibility that involves these three terms: protons, vitamin C and the wide variety of tropical fruits to which our primate ancestors had access to when they walked through the trees.
The flavor to which we attribute the term “sour” has a direct relationship with acidity. According to a study published by the PNAS publication (Proceedings of the National Academy of the United States) this has to do with protons. A research carried out in 2010 in the Emily Liman Sensory Neurobiology laboratory at the University of Southern California points out that “sour-tasting cells in the tongue are equipped with specific proton channels, resulting from the dissociation of the food acids enter taste cells that inform the brain that food is bad. But it is precisely the brain that must decide what to do, whether to eat it or how it can happen often if it is sour, to put on a consistent face”. Therefore, human evolution has caused us to end up identifying certain foods as especially unpleasant for our body, and it is a matter of each one to decide whether to continue taking it or maintain distances.
On the other hand, we have another idea. Humans need ascorbic acid to survive, also known as vitamin C. If we stopped eating it through food we could get scurvy, a life-threatening disease caused by a deficit of this vitamin, which is necessary for the synthesis of collagen in humans. But did you know that more than 61 million years ago, the genes of our past were capable of synthesizing vitamin C? And many mammals can do it, but not us, since according to a study published in the journal Genetica in 2011, “at that time we had such easy and habitual access to it through the fruit that we ingested that we lost the ability to produce it.” Therefore we need to include it in our diet, and our palates have made those flavors in their own way. Not everyone is able to eat certain fruits without making a grumpy face. So, why do we continue making these gestures if it is another product of our day to day and something necessary?
For the professor of the Department of Nutritional Sciences of the University of Rutgers, Paul Breslin, “it is still a kind of rejection response, as a kind of signaling for ourselves and to warn others unconsciously that this food has a special flavor.” That is, something similar to when our tongue eats something that tastes unpleasant or bad, because it is rotten. Flavor cells tell the brain that it should not swallow it.