As mentioned in my previous post, a major compound of green tea is (−)-epigallocatechin-3-gallate (EGCG) — major in that it comprises about 30% of the dry weight of brewed green tea! One of its properties is bitterness, and another is astringency.
Looking into the latter, I discovered something in the literature that makes perfect sense, namely that there are at least two kinds of astringency: the dry-mouth puckering kind and the smooth velvety kind.
You may have heard that astringency is due to precipitation of salivary proteins, but that idea has been completely nixed — there are many very astringent compounds that don’t precipitate salivary proteins at all.
Instead, the dry-mouth puckering kind of astringency that EGCG gives us comes from activation of the trigeminal nerve, the same nerve that gives us the burn of chili peppers.
Up until yesterday, when I read a paper by Schöbel and her colleagues*, I thought that astringency came mainly from activating the hot and cold receptors on trigeminal nerve endings in the mouth — EGCG does activate these receptors, too — but it turns out that there may be a separate receptor for dry/puckering astringency of EGCG on the trigeminal nerve that still needs to be discovered!
Pucker Man by PunkToad, https://www.flickr.com/photos/83699771@N00/22606844807
As for the velvety smooth astringency, that kind comes from compounds similar to EGCG but with a sugar attached. Interestingly, the velvety smooth astringency has a fast-on fast-off quality, while the puckering astringency lasts and lasts after you have swallowed the tea (or wine). Again, no idea what the receptor is, but it is clearly on the trigeminal nerve, too.
More research needed! So exciting!
* Nicole Schöbel et al. Astringency Is a Trigeminal Sensation That Involves the Activation of G Protein–Coupled Signaling by Phenolic Compounds. Chem. Senses 39: 471–487, 2014.
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