Scientists identify compounds that give coffee its distinctive “mouthfeel”
Coffee drinkers intuitively recognize the pleasure of swallowing a soft, rich brew versus a watery one. Aside from the cream or sugar, the coffee itself contributes to this feeling – known as the body or mouth feel – but the specific compounds aren’t well defined. Now researchers are reporting several coffee compounds that contribute to the feeling of the drink covering the inside of the mouth, as well as feelings of astringency and chalk. The results could be used to fine-tune the processing and roasting conditions for specialty coffees.
The researchers will present their results today at the autumn meeting of the American Chemical Society (ACS). ACS Fall 2021 is a hybrid meeting held virtually and in person from August 22-26, and on-demand content will be available from August 30th to September. 30. The meeting includes more than 7,000 presentations on a wide range of scientific topics.
“We knew that coffee itself can affect textural sensations, and it was traditionally believed that this was due to sugars and lipids,” says Christopher Simons, Ph.D., one of the project’s co-lead researchers. “But our team finds that this feeling is actually driven by small molecules, which is kind of unique.” He says that knowledge could help producers and growers make the best coffee. It could also help lovers associate certain properties of a cup of Java with certain compounds, just as wine lovers do.
Brianne Linne, a PhD student presenting the work at the meeting, had previously studied tactile perception on the tongue when the opportunity arose to study coffee bodies. “After our background reading, we found that the definitions of the body of coffee are very vague and sometimes contradicting, so we thought this would be a fascinating topic for us,” she says. Linne is working with Simons and co-principal Devin Peterson, Ph.D., on the project at Ohio State University (OSU).
The team set out to isolate the compounds responsible for the mouthfeel of coffee by first setting up a descriptive analysis panel. They started with four different coffees that the Specialty Coffee Association-licensed reviewers had given varying degrees of physicality. A separate panel of eight experienced tasters who are well versed in tactile awareness then agreed on a series of references that illustrated the sensations that made up each cup.
“In order to better define the term ‘body’, we have broken it down into components that enable us to look for the connections that trigger these special sensations,” says Simons. Four tactile sub-attributes, namely chalk, oral coating, astringency and thickness, were used to distinguish the coffees. They separated the full-bodied coffee into 12 fractions using liquid chromatography and a panel of five tasters examined each fraction. When a majority rated a sub-attribute in a faction heavily, it was further purified to determine the exact link responsible.
The researchers found that a collection of small molecules contributed to the mouthfeel of the coffee. Peterson says they isolated melanoidin compounds formed by the Maillard reaction during roasting and first associated them with astringency. Two compounds, 3- and 4-caffeoylquinic acid, correspond to the mouth coating. Unexpectedly, the feeling subsided with increasing concentration. Peterson says that while biological responses are diverse, it is unusual for an attribute to be perceived at a low level but not at a high level. Eventually they isolated a new chalk-related compound that contains an amino acid.
The team is now interested in whether there are mechanoreceptors in the mouth that recognize these small molecules. According to Peterson, such receptors could be responsible for the decreased feeling of the oral mucosa that occurs with increasing caffeoylquinic acid. You’ll also want to learn more about how the growing conditions and roasting temperatures of coffee beans affect the compounds. With this knowledge, breeders and producers could manipulate their processes to downplay or highlight the small molecules in a cup of coffee according to consumer preferences.
A pre-recorded media briefing on the subject will be available on Tuesday, August 24th at 9:00 p.m. Eastern Time. released www.acs.org/acsfall2021briefings.
The researchers confirm the support and funding from the OSU Flavor Research and Education Center.
Identification and characterization of chemical compounds that contribute to the coffee body
Body is one of ten attributes defined by the Specialty Coffee Association (SCA) that contribute to the overall quality assessment of coffee and thus to the value of the coffee beans. The SCA describes the coffee body as the “tactile feeling” of the liquid in the mouth. This study looked at compounds that affect the tactile sensation of brewed coffee. A descriptive analysis (DA) panel was presented with a series of coffees that received a series of body ratings from certified Q-grade mugs and, through several tastings, identified four tactile sub-attributes that made it possible to differentiate between the presented coffees (“chalk”, “Mouth Coating”, “Astringency” and “Thickness”). A sensory-guided fractionation methodology was then applied, with the coffee with the highest body fraction being subjected to multidimensional separation on a preparative-scale liquid chromatography system equipped with a triple quadrupole mass spectrometry (QqQ-MS) detector. After each dimension of separation, sensory analysis was performed by the trained DA panel to screen for activity using a combined pair comparison and sensory intensity assessment protocol. Phenolic quinic acids and melanoidins were involved in the perception of oral mucosa and astringency, respectively. Compounds were identified using authentic standards and MS / MS fragmentation analysis. Fourier transformed ion cyclotron resonance coupled with MS (FT-ICR MS) was further used to characterize the melanoidin isolate. The concentration ranges of the compound were quantified in coffee using standard addition and sensory recombination tests to further validate the contribution to tactile properties. Psychophysical tests will follow to elucidate the mechanistic foundations. This research provides a molecular basis for understanding how processing and roasting conditions can affect the body and mouthfeel of coffee, and will also contribute to the lack of knowledge about tactile perception in the oral cavity and its relationship to the food and taste experience .