Genetic predisposition plays role in bitter coffee taste

Why does coffee taste more bitter to some people than it does to others? Researchers at the Leibniz Institute for Food Systems Biology at the Technical University of Munich have now come closer to answering this question.

They have identified a new group of bitter compounds in roasted Arabica coffee and have investigated* how they influence its bitter taste. In addition, they demonstrated for the first time that individual genetic predisposition also plays a role in determining how bitter these roasting substances taste.

Although caffeine has been known as a bitter-tasting substance for a long time, even decaffeinated coffee tastes bitter. This shows that other substances also contribute to the bitter taste of roasted coffee.

Coline Bichlmaier, a doctoral student at the Leibniz Institute, explained, “Indeed, previous studies have identified various compound classes that are formed during roasting and contribute to bitterness. During my doctoral thesis, I have now identified and thoroughly analysed another class of previously unknown roasting substances.”

The starting point of her research was the mozambioside contained in Arabica beans. It tastes about 10 times more bitter than caffeine and activates two of the approximately 25 bitter taste receptor types found in the human body, namely the TAS2R43 and TAS2R46 receptors.

“However, our investigations showed that the concentration of mozambioside decreases significantly during roasting, so that it only makes a small contribution to the bitterness of coffee,” said principal investigator Dr Roman Lang. “This prompted us to test whether roasting produces breakdown products of mozambioside that are also bitter and could affect coffee’s taste.”

Coline Bichlmaier and Dr Roman Lang from the Leibniz-Institute for Food Systems Biology at the Technical University of Munich conducting research into coffee flavour in the laboratory. Image credit: G. Olias / Leibniz-LSB@TUM

Combination effect and genetic predisposition are important

As the research team showed, seven different degradation products of mozambioside are formed during roasting. These compounds are found in roasted coffee in varying concentrations, depending on roasting temperature and duration, and almost completely pass into the beverage during brewing.

Investigations in a cellular test system established at the institute show that these roasting substances activate the same bitter taste receptor types as mozambioside. Three of the roasting products even had a stronger effect on the receptors than the original compound.

However, the researchers found that the concentrations of these roasting products measured in brewed coffee were too low to induce a noticeable taste on their own. Only the combination of mozambioside and its roasting products in a sample led eight out of 11 test subjects to perceive a bitter taste. One person found the taste astringent and two did not perceive any particular taste.

A genetic test showed that taste sensitivity depended on the genetic predisposition of the test subjects: two people had both copies of the TAS2R43 gene variant defective. Seven had one intact and one defective variant of the receptor and only two people had both copies of the gene intact.

What do these results mean for the future?

“The new findings deepen our understanding of how the roasting process influences the flavour of coffee and open up new possibilities for developing coffee varieties with coordinated flavour profiles. They are also an important milestone in flavour research, but also in health research,” Lang said. “Bitter substances and their receptors have further physiological functions in the body, most of which are still unknown.”

According to Lang, there is still a lot of work to be done, since for many bitter substances in coffee alone, it is not yet known which bitter taste receptors they activate, even though millions of people worldwide drink coffee every day.

_{*Publications: 1) Bichlmaier, C., Fröhlich, S.M., Brychcy, V., Grassl, A., Behrens, M., and Lang, R. (2024). Contribution of mozambioside roasting products to coffee's bitter taste. Food Chem 469, 142547. 10.1016/j.foodchem.2024.142547. 2) Czech, C., Lang, T., Graßl, A., Steuer, A., Di Pizio, A., Behrens, M., and Lang, R. (2024). Identification of mozambioside roasting products and their bitter taste receptor activation. Food Chem 446, 138884. 10.1016/j.foodchem.2024.138884.}

Top image credit: iStock.com/nicoletaionescu