Astringent mouthfeel of wine results from a lubrication failure in the mouth

April 14, 2016, Wiley
Astringent mouthfeel of wine results from a lubrication failure in the mouth

We are all familiar with that strange feeling in the mouth after a sip of red wine or tea, or a bite of unripe fruit. It has been described as dry, leathery, or even furry. This astringent effect is caused by tannins or polyphenolic compounds that bind to mucins, lubricating proteins in the mucus membranes of the mouth. In the journal Angewandte Chemie, a Chinese and Korean research team has now shown the relationship between astringency and disrupted lubrication of the oral cavity.

Mucins consist of a central protein chain with side chains made of sugar compounds that can bind a large amount of water. Mucins form a barrier and protect sensitive from drying out and from chemical and mechanical interactions. They provide adequate lubrication and correspondingly low friction. This lubricating film in the fails when tannins get into the act: a sip of wine causes the tongue to feel less slippery.

This friction aspect has now been more closely studied by a team working with Feng Zhou. The scientists from the Chinese Academy of Sciences (Lanzhou, China) and the Korea Advanced Institute of Science and Technology (KAIST, Daejeon, Republic of Korea) used a dumbbell-shaped mucin extracted from oral mucus membranes and tannic acid, a star-shaped polyphenol found in wine and unripe fruit, as their tannin. When the tannic acid binds to the mucin, their interactions reduce the solubility of the protein in water. The mucins consequently aggregate and may precipitate, leading to a failure of the mucin lubrication film.

The quartz crystal microbalance (QCM) technique was employed for monitoring adsorption and precipitation of proteins induced by tannic acid molecules. Atomic force microscopy of a substrate coated in mucin showed a flat, dense, film. After addition of tannic acid, many "defects" could be seen in the film and the surface was significantly rougher.

The researchers determined the friction between a soft plastic ball and a glass surface coated with mucin. In comparison to a surface coated only with water, the mucin-coated surface had much lower friction. Addition of tannic acid caused the friction to rise substantially. An extract of coffee beans, which also contain tannins, had a similar effect.

In order to mimic a tongue, the scientists produced a mucin-containing plastic hydrogel. When wet, this elastic but barely tear-resistant material had very low friction, slipping easily through the fingers. A weight placed on an inclined surface of this hydrogel slides right off. Addition of a tannic acid solution makes the gel sticky and it begins to shrink as a result of losing water. The mechanical strength increases significantly and the elasticity decreases. The weight no longer slides off.

Bioactive proteins that maintain the slippery state of fish skin also react to tannins. The researchers made gloves that release tannic when touched. These gloves made it easy to grasp and hold fish.

Explore further: Researchers discover mechanism for fixing defective mucins

More information: Shuanhong Ma et al. Astringent Mouthfeel as a Consequence of Lubrication Failure, Angewandte Chemie International Edition (2016). DOI: 10.1002/anie.201601667

Related Stories

Researchers discover mechanism for fixing defective mucins

October 2, 2015

Proper lubrication is crucial to keep not only machines but also humans functioning smoothly. The mucus membranes in our mouths, eyes, stomachs and genital area help keep friction to a minimum and also protect us against ...

Nothing to sneeze at—battling mucus to beat cancer

March 9, 2016

What do cancer cells and a runny nose have in common? The answer is mucus; and researchers at the Stephenson Cancer Center at the University of Oklahoma have shown it may hold the key to making cancer treatment better.

Salivary mucins play active role to fight cavities

November 11, 2014

Salivary mucins, key components of mucus, actively protect the teeth from the cariogenic bacterium, Streptococcus mutans, according to research published ahead of print in Applied and Environmental Microbiology. The research ...

Recommended for you

Nanodiamonds as photocatalysts

October 19, 2018

Climate change is in full swing and will continue unabated as long as CO2 emissions continue. One possible solution is to return CO2 to the energy cycle: CO2 could be processed with water into methanol, a fuel that can be ...

Producing defectless metal crystals of unprecedented size

October 19, 2018

A research group at the Center for Multidimensional Carbon Materials, within the Institute for Basic Science (IBS), has published an article in Science describing a new method to convert inexpensive polycrystalline metal ...

Shining light on the separation of rare earth metals

October 18, 2018

Inside smartphones and computer displays are metals known as the rare earths. Mining and purifying these metals involves waste- and energy-intense processes. Better processes are needed. Previous work has shown that specific ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.