German researchers have discovered the bioactive compounds that give coffee a bitter taste. They say their findings could help the F&B industry control roasting processes according to consumer preferences.  

Coline Bichlmaier and Dr. Roman Lang, researchers from the Leibniz Institute for Food Systems Biology at the Technical University of Munich, identified a new group of bitter compounds in roasted Arabica coffee.

They also demonstrated for the first time that genetic predisposition plays a role in determining how bitter these roasting substances taste. Speaking to Food Ingredients First, Lang says the findings came as no surprise.

“We expected a result along these lines. In cell experiments, we investigated individual pyrolysis products of the bitter coffee compound mozambioside on individual bitter receptors. The results showed that mozambioside and its pyrolysis products only address two of the 25 human bitter receptors, namely TAS2R43 and TAS2R46,” he says.  

“As it is known that the receptor TAS2R43 is not functionally expressed in 20% of the European population, it was to be expected that participants lacking TAS2R43 would perceive these compounds as less bitter.” 

“Coffee contains many bioactive compounds, such as the stimulating caffeine or antioxidants. It has been known for some time that bitter receptors not only serve the perception of bitter taste but are also expressed outside the oral cavity in various tissues, wher they perform functions that have been little studied so far.”

Locating bitter compounds

Although caffeine is well established as a bitter tasting substance, decaffeinated coffee also tastes bitter. This shows that other substances also contribute to the bitter taste of roasted coffee, the researchers say. 

Mozambioside tastes about ten 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. 

“With the water-soluble roasting products of mozambioside, another class of compounds is now known to enter the body during coffee consumption and may have physiological effects. In our quantitative studies, we show how these bioactive roasting products are formed depending on the roasting process,” Lang says. 

“This gives the coffee industry the opportunity to control the amount of this bioactive compound class in the final product according to consumer preferences. We aim to further investigate what effects mozambioside and its roasting products have, beyond the bitter taste perception, in the human body.”

“The subject of bitter receptors expressed outside the oral cavity and their roles in the human body is particularly interesting,” he continues. “In this regard, we are investigating how mozambioside and its roasting products are absorbed by the body, how they interact with bitter receptors, how they are metabolized, and which breakdown products with potentially health-relevant effects circulate in the bloodstream.” 

Roasting parameters 

Since TAS2R43, the bitter receptor that is not functionally expressed in every fifth person in Europe, may be linked to bioactivity, in future studies it will be important to further explore how the lack of this receptor in certain genotypes affects the bioactive compounds’ influence on the body, says Lang. 

“Our findings show that although coffee appears to be well-researched, there are still fascinating and undiscovered compound classes that could be associated with bioactive functions in the human body. The formation of these compounds strongly depends on the roasting parameters and, of course, the coffee variety.”

“This means their formation and, therefore, their effects on the body of the coffee drinker can be precisely controlled. Our research not only uncovers new bioactive substances in coffee but also contributes knowledge on how coffee roasting can be tailored to create a more personalized and health-conscious coffee experience,” he concludes.