Why do some individuals find coffee more bitter than others? Researchers from the Leibniz Institute for Food Systems Biology at the Technical University of Munich have made strides toward uncovering the answer. They have pinpointed a novel set of bitter compounds found in roasted Arabica coffee and explored their role in the coffee’s bitter flavor. Additionally, they have demonstrated for the first time that one’s genetic makeup also influences how these compounds are perceived in terms of bitterness.
Why is coffee perceived as more bitter by some individuals than by others? Researchers at the Leibniz Institute for Food Systems Biology at the Technical University of Munich are closer to solving this puzzle. They have discovered a new class of bitter compounds in roasted Arabica coffee and examined their impact on its bitterness. Furthermore, they have shown for the first time that genetic factors also affect how bitter these compounds taste to different people.
While caffeine is a well-known bitter compound, decaffeinated coffee retains a bitter flavor, indicating that other elements contribute to the bitterness of roasted coffee. Coline Bichlmaier, a PhD candidate at the Leibniz Institute, notes, “In fact, previous research has identified numerous compound categories that emerge during roasting and add to the bitterness. In my doctoral work, I’ve now uncovered and thoroughly examined another set of previously unrecognized roasting compounds.”
The focus of her research was on mozambioside, which is present in Arabica beans. This compound is about ten times more bitter than caffeine and triggers two of the roughly 25 types of bitter taste receptors in humans: TAS2R43 and TAS2R46. “However, our research revealed that the level of mozambioside diminishes significantly during roasting, which means it contributes only a little to the bitterness of coffee,” explains lead researcher Roman Lang, adding, “This led us to investigate whether the products formed from the breakdown of mozambioside during roasting might also have a bitter taste and contribute to coffee’s overall flavor.”
Combination Effect and Genetic Influence Matter
The research team found that seven different breakdown products of mozambioside are created during roasting. The levels of these compounds vary depending on the roasting temperature and time, and most of them transfer into the brewed coffee.
Tests conducted in a specialized cellular system at the institute revealed that these roasting byproducts activate the same bitter taste receptors as mozambioside. Notably, three of these roasting products had an even stronger impact on the receptors than the original compound. However, the researchers observed that the concentrations of these compounds in brewed coffee were too low to elicit a noticeable taste on their own. It was only when the researchers combined mozambioside with its roasting byproducts that eight out of eleven participants could taste a bitterness. One person described the flavor as astringent, while two others did not report perceiving any distinct taste.
Genetic analyses indicated that taste sensitivity varied among participants: two individuals had defects in both copies of the TAS2R43 gene variant. Seven had one normal and one defective variant, and only two maintained intact copies of the gene.
What Do These Findings Mean for the Future?
“These new insights enhance our understanding of how roasting affects the flavor profile of coffee and pave the way for creating coffee varieties with tailored flavor characteristics. They also represent a significant step in flavor and health research,” explains Roman Lang. He notes, “Bitter substances and their corresponding receptors perform additional physiological functions in the body, many of which remain unexplored.” According to Lang, there’s much work ahead, as the specific bitter receptors activated by numerous bitter compounds in coffee are still unknown, despite millions of people worldwide enjoying coffee daily.
Further Information
Mozambioside
Arabica coffee contains the bitter compound known as mozambioside (11-O-β-D-glucosyl-cafestol-2-one). It is a water-soluble derivative of cafestol that is particularly prevalent in naturally caffeine-free varieties. Its detection threshold in humans is 60 ± 10 micromolar (Lang et al., 2015; Lang et al., 2020). The concentration of mozambioside in raw Arabica coffee ranges from about 0.4-1.2 micromol/g. During roasting, its level decreases to below the threshold for taste in the final product.
Other Bitter Compounds Formed During Roasting
Prominent bitter compounds that are reported to form during roasting include caffeoylquinides (which originate from chlorogenic acids), diketopiperazines (derived from coffee proteins), and oligomers of 4-vinylcatechols (produced from caffeic acids). While these compounds contribute to bitterness, the specific bitter taste receptors responsible for their detection are still unidentified.
Bitter Taste Receptors
Humans have about 25 types of taste receptors that discern bitter substances. These receptors are not limited to the mouth; they are also present in various other organs and tissues. The various roles they play there are under investigation in multiple studies, including those at the Leibniz Institute for Food Systems Biology at the Technical University of Munich. Initial research suggests that bitter taste receptors in the respiratory system help defend against pathogens and enhance ciliary movement. Other studies indicate that these receptors in the intestines and blood cells may support immune responses or play a role in metabolic regulation.
