Compounds that give coffee its distinctive 'mouthfeel'

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People who drink coffee intuitively know the difference between a rich, smooth brew and one that is watery. The coffee itself is responsible for this sensation, which is known as body or mouthfeel. However, it is not clear what the exact compounds are. Researchers now report that there are several compounds in coffee that contribute to the sensation of the beverage coating the insides of the mouth. They also describe the sensations of astringency or chalkiness. These results could be used for optimizing processing and roasting conditions in specialty coffees.

Today, the researchers will present their findings at the American Chemical Society's fall meeting.

Christopher Simons, Ph.D. is one of the co-principal investigators of this project. "We know that coffee can have an impact on textural sensations. It was previously thought that sugars and oils were responsible." Our team discovered that small molecules may be responsible for this sensation, which is quite unique. This knowledge could be used to help growers and producers make the best coffee. This knowledge could also help coffee enthusiasts attribute specific compounds to certain characteristics of their cup of java, much like wine lovers do.

Brianne Linne is a graduate student who will present the work at the meeting. She had previously studied tactile perception of the tongue and coffee body when she was offered the chance to do so again. She says, "From our background readings, we found definitions for coffee body to be vague and sometimes contradictory. So we thought this would be an interesting topic for us to research." Linne works with Simons, and Devin Peterson (Ph.D.), as co-principal investigator on the project at The Ohio State University.

They set out to identify the compounds that influence coffee's mouthfeel. To do this, they first created a descriptive analysis panel. The team started with four coffees that had received varying body ratings from evaluators who were licensed by the Specialty Coffee Association. Eight experienced tasters who are skilled in tactile awareness agreed to a list of references that illustrated how each cup differs from the others.

Simons says, "To better define the term body, we broke it into components that would permit us to search for the compounds driving these particular sensations." To distinguish the coffees, four tactile sub-attributes were used, including chalkiness, mouthcoating and thickness. The full-body coffee was separated into 12 fractions by liquid chromatography. Each fraction was screened by five tasters. A majority of the fractions were ranked strongly for a sub-attribute. The fraction was then further purified to identify the compound.

Researchers discovered that coffee's mouthfeel is a result of a group of small molecules. Peterson claims that they have identified melanoidin compounds from the Maillard reaction in roasting and associated them with astringency for the first time. The mouthcoating is represented by two compounds, 3-caffeoylquinic and 4-caffeoylquinic acids. The sensation diminished with increasing concentrations, which was unexpected. Peterson states that biological reactions are complex and can be perceived at different levels. However, it is not common for one attribute to be perceived at low levels but not at high levels. They also discovered a new compound that was related to chalkiness and contained an amino acid.

Now, the team wants to know if mechanoreceptors are present in the mouth that can detect small molecules. Peterson believes that such receptors may be responsible for the diminished mouthcoating sensation associated with increased caffeoylquinic acids. They want to learn more about the effects of roasting temperature and coffee bean conditions on these compounds. This knowledge will allow producers and growers to adjust their processes to highlight or downplay the small molecules in coffee, depending on consumers' preferences.

Continue reading Spilling the beans to discover coffee's true identity

Additional information: Identification of chemical compounds that contribute to coffee body, ACS Fall 2021.