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red currants. © INRA, PITSCH Michel

The secrets of astringency revealed through UV radiation

When you eat a sour red currant or drink a cup of tea or wine, you may feel as if your mouth were suddenly dry – this is astringency. For the first time, the molecular interactions responsible for this sensation have been identified by researchers from INRA, the Université Paris-Sud and the CNRS, in collaboration with teams from the French national synchrotron facility SOLEIL(1), using a new method of UV radiation analysis. Their research has been published on the Angewandte Chemie journal’s website.

Updated on 10/28/2013
Published on 07/23/2013

Astringency is an important part of the pleasure we derive from certain dishes or beverages and adds to their characteristics. It is caused by the interaction between tannins (substances produced by plants) and PRPs (proline-rich proteins) (2) in saliva. PRPs bind to tannins before they enter the digestive system and shrink the mucus membranes inside the mouth, causing the feeling of dryness in the mouth so typical of astringency.

While researchers from INRA’s Sciences for Oenology Joint Research Unit have shown how PRPs envelop the tannins to trap them (3), the exact site of interaction between the two substances had not yet been clearly identified. These proteins are called “intrinsically disordered” proteins – meaning they do not have a well-defined three-dimensional structure. This makes using traditional analysis methods (biocrystallography, NMR) difficult, if not impossible, to study their structure.

A first: UV synchrotron radiation analysis

The researchers from INRA, Université Paris-Sud, CNRS and SOLEIL Synchrotron used a new method developed at SOLEIL that involves vacuum ultraviolet synchrotron radiation coupled with mass spectrometry to locate the interaction site of a tannin on the PRP (protein IB5) for the first time.

Using the radiation energy from the synchrotron to target the PRP-tannin structure, researchers were able to show that although the tannin was fragmented, fragile links between the two substances remained intact. The PRP fragments that remained attached to the tannin were then analysed using mass spectrometry, enabling researchers to identify the sections of the protein the tannin binds to. Not only has this technique made it possible to study the interactions between PRPs and tannins, but it leads the way to a universal method that is especially adapted to studying intrinsically disordered proteins that are so elusive to other techniques. Other potential study subjects include proteins that regulate cell function and those involved in certain illnesses.

Study of the interaction sites of noncovalent complexes using a new method that couples mass spectrometry and VUV (vacuum ultraviolet) synchrotron radiation.. © INRA, Francis Canon
Study of the interaction sites of noncovalent complexes using a new method that couples mass spectrometry and VUV (vacuum ultraviolet) synchrotron radiation. © INRA, Francis Canon

(1) Involved in the study: Centre for Taste, Food and Nutrition Sciences (INRA/CNRS/Université de Bourgogne), Laboratory of Physical Chemistry (Université Paris-Sud/CNRS), Synchrotron SOLEIL, Sciences for Oenology Joint Research Unit (INRA/Montpellier SupAgro/Université Montpellier 1), University of Belgrade.
(2) Proline is a non essential amino acid.
(3) Reference: F. Canon, R. Ballivian, F. Chirot, R. Antoine, P. Sarni-Manchado, J. Lemoine, P. Dugourd, J. Am. Chem. Soc. 2011, 133, 7847-7852.

Contact(s)
Scientific contact(s):

  • Francis Canon (33 (0)3 80 69 35 29 ) Centre for Taste, Food and Nutrition Sciences (INRA/CNRS/Université de Bourgogne)
  • Alexandre Giuliani (33 (0)1 69 35 97 29) Synchrotron SOLEIL
Press Relations:
INRA News Office (33 (0)1 42 75 91 86)
Associated Division(s):
Science for Food and Bioproduct Engineering
Associated Centre(s):
Bourgogne-Franche-Comté

References

Francis Canon, Aleksandar R. Milosavljević, Guillaume van der Rest, Matthieu Réfrégiers, Laurent Nahon, Pascale Sarni-Manchado, Véronique Cheynier and Alexandre Giuliani. Photodissociation and Dissociative Photoionization Mass Spectrometry of Proteins and Noncovalent Protein-Ligand Complexes. Angewandte Chemie, online 19 July 2013, DOI: 10.1002/anie.201304046

F. Canon, F. Paté, E. Meudec, T. Marlin, V. Cheynier, A. Giuliani, P. Sarni-Manchado, Anal. Bioanal. Chem. 2009, 395, 2535-2545.

F. Canon, F. Paté, V. Cheynier, P. Sarni-Manchado, A. Giuliani, J. Pérez, D. Durand, J. Li, B. Cabane, Langmuir 2013, 29, 1926-1937