Tannins are polyphenolic compounds that are responsible for the bitterness and astringency of red wines. Certain foods reduce these sensations, improving the flavor of a wine. However, how this works exactly is not well understood. Some studies have indicated that tannins interact with lipids at the molecular level. In foods, lipids are found as fat globules dispersed in liquids or solids.

Julie Géan, University of Bordeaux, Pessac, France, and colleagues have investigated how tannins influence the size and stability of lipid droplets in an emulsion. They also evaluated how the prior consumption of vegetable oils impacts the taste of tannins for human volunteers. The researchers prepared an oil-in-water emulsion using olive oil, water, and a phospholipid emulsifier. Then, they added a grape tannin, called catechin, and studied the lipids in the emulsion using optical microscopy, electron microscopy, and NMR spectroscopy. Droplet size distributions were measured using static light scattering. The team found that the tannin inserted into the layer of emulsifier that surrounded the oil droplets, causing larger droplets to form.

In taste tests, volunteers indicated that consuming a spoonful of rapeseed, grapeseed, or olive oil before tasting a tannin solution reduced the astringency of the compounds. Olive oil had the greatest effect, causing the tannins to be perceived as fruity instead of astringent. Combining the biophysical and sensory results, the researchers concluded that tannins can interact with oil droplets in the mouth, making them less available to bind to saliva proteins and cause astringency.

• New Insights into Wine Taste: Impact of Dietary Lipids on Sensory Perceptions of Grape Tannins,
  Ahmad Saad, Julien Bousquet, Nora Fernandez-Castro, Antoine Loquet, Julie Géan,
  J. Agric. Food Chem. 2021.
  https://doi.org/10.1021/acs.jafc.0c06589