By Jacob Webster-Jones
- Astringency can be caused by several different classes of compounds and is a sensation rather than a flavor or taste
- The prevailing theory around the perception of astringency has to do with the binding of astringent compounds to salivary proteins which cause an increase in friction which is felt on the surface of the tongue
- pH plays a role in the perception of astringency but an exact mechanism is not clear yet
What is astringency?
If you taste black coffee, tea, or even baker’s chocolate there is a distinct sensation in the mouth that causes your tongue to feel like it’s tightening up and puckering. This is referred to as “astringency” and is often commonly associated with bitter taste. Unlike the five tastes – sweet, sour, bitter, umami, and salty – astringency is a sensation rather than a flavor or taste. So what exactly causes foods to become astringent?
We can attribute certain flavors to specific volatiles, sweetness to sugars, sour to acids, umami to proteins, and bitter to alkaloids but what about this puckering sensation? The answer is a little long, complicated, and involves way more information about what makes up saliva than I ever would have thought. For those of us who want a quick and simple answer the only thing I can really say for certain is that it has something to do with some of the proteins in solution in your saliva and how they interact with other compounds within a food matrix.
What causes and affects astringency?
There isn’t a single molecule or class of molecules that cause the sensation of astringency and therefore there are multiple reasons why astringent foods cause their characteristic sensation which makes it difficult to determine their exact mechanism. The classic thought on how we perceive astringency is through trigeminal nerves which convey sensations like burning from spice, heat, and cold. These nerves are different than the olfactory nerves that are used to distinguish flavors (Morten C. Meilgaard, 2015).
Huang and Xu published a review paper in Comprehensive Reviews in Food Science and Food Safety which offers a more in-depth view on the physiological reasons why humans perceive astringency in phenols which goes a little into genetics and the proline-rich proteins in saliva. The review shows the idea that phenols will bind with the proteins in saliva and cause them to precipitate. The resulting precipitate then causes a loss of lubricity and increase in friction on the tongue.
The combination of the effects is what is largely thought to be the cause of astringent sensations (Huang & Xu, 2021). While the review talks mainly about how phenolic rich foods such as berries and wines elicit astringent sensations, they do mention other compounds such as multivalent salts, proteins, organic and mineral acids, and dehydrating agents can do the same but possibly through different mechanisms. Aluminum sulfate, zinc, copper, magnesium, and calcium have been shown to cause astringency but their exact mechanism has yet to be reliably established. Organic acids have shown an inverse relationship between pH and perceived astringency, so as pH decreases, total astringency increases (Bajec & Pickering, 2008).
The pH of a food affects not only the total astringency but also how intense we perceive it. In an experiment where participants consumed equal concentrations of tannins but at different pH levels, researchers found that the drink with the lower pH was perceived as more astringent than the drink at a higher pH despite having the same amount of total tannins. This relationship could be due to having more favorable charges on salivary proteins and astringent compounds, which would allow them to bind more efficiently (Bajec & Pickering, 2008).
Much of the research conducted on astringent compounds is around phenolic compounds due to their potential health benefits as antioxidants and its relationship to consumer acceptability (Bajec & Pickering, 2008). Understanding more about what causes astringency can allow food producers to alter how astringent their products are to make them more desirable or even make foods more nutritious by adding phenols and minerals into foods while limiting sensory impacts.
Bajec, M. R., & Pickering, G. J. (2008). Astringency: mechanisms and perception. Crit Rev Food Sci Nutr, 48(9), 858-875. doi:10.1080/10408390701724223
Huang, R., & Xu, C. (2021). An overview of the perception and mitigation of astringency associated with phenolic compounds. Compr Rev Food Sci Food Saf, 20(1), 1036-1074. doi:10.1111/1541-4337.12679
Morten C. Meilgaard, G. V. C., B. Thomas Carr. (2015). Sensory Evaluation Techniques (Fifth ed.). Boca Raton, FL: CRC Press.
Photo by Govinda Valbuena: https://www.pexels.com/photo/man-in-black-crew-neck-top-1054048/
Jacob Webster-Jones | Linkedin
IFTSA VP of Digital and Social Media (2021-2022)
Jacob found his passion for food science while on an elementary school field trip to a R&D lab in San Antonio, Texas. Since then he has been interested in why food behaves the way it does and how it can be used to improve people’s quality of life. He is currently pursuing his bachelor’s degree in Food Science & Technology from Texas A&M University and is the current president of his school’s food science club and IFTSA chapter. After he graduates, Jacob plans on going to work for a few years before returning to start a graduate degree, his ultimate goal is to work in research and development for a flavor company. On the off chance he has free time you can find him experimenting in the kitchen or enjoying the outdoors.
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