To the bitter end
Red wine, beer, dark chocolate and coffee — some of us love the complexity of these bitter flavours while others find them overwhelming and unappealing.
We may think it’s just getting older that helps us to acquire our increasing appreciation of bitter things, but new research out this week shows it may actually be something we can train — thanks to our saliva.
Saliva is a wonderful liquid filled with compounds that help us to digest, molecules that help transport smells from our food to our noses for improved taste, and proteins that can affect how things taste.
We use it to help lubricate our mouths, making chewing and swallowing easier — our saliva also coats our teeth, protecting them from an environment of acidic drinks and plaque bacteria.
One particular component of saliva — a group of proteins called proline-rich proteins or PRPs affect the way we experience bitter foods. They do it by binding to polyphenols, the substances that are perceived as bitter and astringent in our mouths.
Our aversion to bitter foods is a good thing and it likely started out as a way for us to avoid eating toxic plants and berries.
Taste cells on our tongue detect sugars, amino acids, acids and minerals, which are usually experienced as sweet, umami, butter, sour and salty tastes.
Bitterness, however, acts as a warning mechanism against toxic or harmful chemicals, helping evoke reactions such as spitting out the potentially dangerous food and learning to avoid it in the future.
People who produce more proline-rich protein in their saliva tend to enjoy bitter foods more as their saliva is able to remove the perception of bitterness by binding with the polyphenols. What wasn’t known was whether or not the amount of PRP produced by an individual was fixed, or if it could be changed. Doing so could mean that those of us who don’t like bitter foods could eventually find a pleasant way to experience them. The hope that it was changeable came from previous research on rodents that showed that the expression of proteins in their saliva could be altered by feeding them a bitter diet. To test this, researchers at Purdue University took 64 volunteers and gave them an alternating diet over a six week period. On some of the weeks, the volunteers were not allowed to eat any bitter foods and had to provide multiple saliva samples that were collected at different times.
On the other weeks, the volunteers were given three glasses of a lowsugar, bitter chocolate almond milk a day. Chocolate was chosen because it contains high levels of the bitter polyphenols. Again, the volunteers had to provide saliva samples throughout the week.
The researchers measured the protein composition of the volunteers’ saliva throughout the stages of the controlled diet experiment. They found that after the volunteers’ exposure to bitter polyphenols, the volunteers did produce more of the PRP. The more PRPs the volunteers produced, the less bitter they reported that the chocolate milk tasted.
These results suggest that through bitterness training we might be able to naturally build up more PRPs in our saliva just by exposing ourselves to increasing amounts of bitter foods over time.
Perhaps dedicated training centres could help us to build up enough PRP to appreciate the complex flavours in red wine and dark chocolate in a saliva bonded to give us a delicious taste experience.
For now, those of us with leafygreen-avoiding children might want to start a new experiment and sneak in small amounts of these bitter foods to their daily routine and perhaps one day they will grow up into broccoliloving young people.
Dr Michelle Dickinson, creator of Nanogirl, is a nanotechnologist who is passionate about getting Kiwis hooked on science and engineering. Tweet her your science questions @medickinson