Soft Matter Blog

Tannins are well known to influence the taste of food and drinks, in particular red wine. This has to do with the astringent sensation that the tannins produce in the mouth; a dry and puckering effect. Tannins are water soluble polyphenols that interact with proteins and precipitate them out. They are produced by plants as part of their defence mechanism against parasitic invasion. The tannins bind to enzymes released by the parasite causing the enzyme to precipitate. The enzyme is rendered useless and the invasion halted.

The binding of tannins to proteins also occurs in our bodies when we eat or drink tannin-containing foods. In the mouth the interaction between tannins and saliva causes astringency. Tannins are also known to bind to our digestive enzymes resulting in a reduced ability to digest food. If consumed in large quantities tannins can lead to serious malnutrition. So why is it that we can drink, for example, red wine and not die? Bernard Cabane at the ESPCI Paris has been trying to answer exactly this.

Cabane and coworkers have been investigating the interactions between salivary proline-rich proteins and the tannins present in green tea. Their work concentrates on two salivary proteins, one glycosylated and one non-glycosylated, with the same polypeptidic backbone. For the non-glycosylated protein the tannins are observed to bind randomly along the protein chain. The chains have very extended conformations, which may make it more efficient at binding the tannins. Increasing the tannin concentration results in the formation of protein-tannin aggregates and precipitation of the proteins, once the concentration is high enough. The precipitation of the protein degrades the lubrication in the mouth resulting in an astringent sensation. Since precipitation only occurs once the threshold concentration of tannins to proteins is reached, Cabane suggests that it may act as a warning system telling us when the tannin levels in our body are too high.

For the glycosylated protein, on the other hand, no precipitation is observed in the presence of tannins. Instead globular aggregates, resembling micelles,  form with the hydrophilic sugars on the outside and the hydrophobic residues of the protein backbone, which bind the tannins, on the inside. These micelles act as tannin traps with roughly 1000 tannins locked within each micelle. The efficient binding of the tannins in the micelle, means that the tannins can enter the digestive system with no adverse effects on the body.

Cabane is also interested in the oxidisation of tannins and the effect it has on the flavour of foods.

H. Boze et al., Proline-rich salivary proteins have extended conformations, Biophysical Journal,  2010.

Pascal, C et al., Aggregation of a proline-rich protein induced by epigallocatechin gallate and condensed tannins: Effect of protein glycosylation, Journal of Agricultural and Food Chemistry, 2008.

Vernhet, A et al., Characterization of oxidized tannins: comparison of depolymerization methods, asymmetric flow field-flow fractionation and small-angle X-ray scattering, Analytic and Bioanalytical Chemistry, 2011.

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Do you know someone who deserves recognition for their contribution to the soft matter field?

Now is your chance to propose they receive the accolade they deserve.

Nominations are currently being accepted for the 2012 Soft Matter Lectureship. This annual Lectureship was established by the journal in 2009 to honour a younger scientist who has made a significant contribution to the soft matter field.
Michael J. Solomon, University of Michigan Ann Arbor, was the 2011 winner.  Solomon’s research addresses questions about the structure and function of soft matter. 

Nominations for the 2012 Soft Matter Lectureship close on 31 March 2012.

Qualification

To be eligible for the Soft Matter Lectureship, the candidate should be in the earlier stages of their scientific career, typically within 15 years of attaining their doctorate or equivalent degree, and will have made a significant contribution to the field.

Description

The recipient of the Lectureship will be asked to present a lecture three times, one of which will be located in the home country of the recipient. The Soft Matter Editorial Office will provide the sum of £1000 to the recipient for travel and accommodation costs.

The recipient will be presented with the Lectureship at one of the three lectures. They will also be asked to contribute a lead article to the journal and will have their work showcased on the back cover of the issue in which their article is published.

Selection

The recipient of the Lectureship will be selected and endorsed by the Soft Matter Editorial Board.

Nominations

Those wishing to make a nomination should send details of the nominee, including a brief C.V. (no longer than 2 pages A4) together with a letter (no longer than 2 pages A4) supporting the nomination, to the Soft Matter Editorial Office (softmatter-rsc@rsc.org) by 31 March 2012.  Self nomination is not permitted.