Study reveals which substances make coffee bitter

Monday, 22 June, 2020

Study reveals which substances make coffee bitter

A recent study conducted by the Leibniz-Institute for Food Systems Biology and the Technical University of Munich (TUM) into bitter substances in coffee has provided new insights into the molecular interactions between bitter substances and bitter receptors. Compounds contained in coffee such as caffeine contribute to the bitterness in varying degrees. The findings were published in the Journal of Agricultural and Food Chemistry.

Caffeine is a well-known bitter coffee constituent; however, it is not solely responsible for the bitter taste of coffee. Findings from a study conducted by the Freising team of scientists confirm this. Using a cell-based testing system — a type of artificial tongue — and docking analyses, researchers investigated five different bitter coffee constituents. The tests included mozambioside, a bitter substance identified in Arabica beans, its roast product bengalensol and other well-known coffee compounds, cafestol, kahweol and caffeine.

Based on the results of the study, researchers assume that mainly two of the 25 human bitter taste receptors respond to the coffee’s constituents. While a relatively high concentration of caffeine is necessary to stimulate the TAS2R46 and TAS2R43 receptors, smaller amounts of the other four substances are needed. The caffeine concentration required to activate the TAS2R43 bitter taste receptor to the same degree as mozambioside or bengalensol was about 30 to 300 times higher, respectively, according to lead author Tatjana Lang.

Further studies conducted by researchers suggest that the bitter substances in coffee interact with each other. Studies showed that kahweol and mozambioside exhibit similar binding properties for the TAS2R43 bitter taste receptor. Compared to mozambioside, however, kahweol receptor activation was relatively weak and, depending on the dose, was capable of inhibiting the mozambioside-induced activation of the bitter taste receptor.

“We therefore assume that kahweol can reduce the bitter taste elicited by TAS2R43 by suppressing more effective bitter substances at the receptor,” said Maik Behrens, principal investigator and head of the research group Taste Systems Reception & Biosignals at the Leibniz-Institute.

This effect could play a role in coffee preparations that do not include a filtering step like espresso or Turkish coffee, which are beverages that contain kahweol.

“Our findings indicate that bitter coffee substances quite specifically activate two of the 25 bitter taste receptors. We know that both types of receptors are present not only in taste cells. TAS2R43 is also present in the stomach and in conjunction with caffeine plays a role in the regulation of gastric acid secretion. The question now arises as to how coffee constituents like bengalensol, which activate the receptor with much higher potency, might be involved in this regulatory process,” Behrens said.

Findings also revealed that many people do not possess the TAS2R43 bitter taste receptor due to a genetic variation. This could explain the differences in individual coffee taste perception or its tolerability; however, more research is needed to understand the complex interaction of bitter substances, bitter receptors and their effects on the human body.

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