Astringent

Agrimoniin is a 1,871 Da hydrolysable tannin carrying four hexahydroxydiphenoyl groups and 52 oxygens, and astringency is the direct physical consequence: multivalent phenolic hydroxyls hydrogen-bond and precipitate proteins, tightening mucosal surfaces.

In its signature plants it is the dominant polyphenol outright, 94% of the total polyphenols of Agrimonia procera stem and over 90% of its seed ^{1Reference 1Karlińska E et al. · 2021The aerial parts of Agrimonia procera Wallr. and Agrimonia eupatoria L. as a source of polyphenols, and especially agrimoniin and flavonoidsView study →}, the single most abundant compound in strawberry leaf at 3–8% of dry matter ^{2Reference 2Fecka I et al. · 2022Fragaria × ananassa cvView study →}, and about 2.5% of tormentil rhizome inside a total tannin content above 20% ^{3Reference 3Fecka I et al. · 2015Quantification of tannins and related polyphenols in commercial products of tormentil (Potentilla tormentilla)View study →}.

Where agrimony, tormentil or strawberry leaf act as astringents, this is the molecule doing most of it.

The mechanism is class chemistry rather than a named receptor, and no agrimoniin-specific protein-precipitation index has been published, so the assignment rests on structure plus documented dominance.

Astringency is luminal and topical by definition, which is the only place this molecule ever is ^{4,5,6Reference 4Piwowarski JP et al. · 2014Role of human gut microbiota metabolism in the anti-inflammatory effect of traditionally used ellagitannin-rich plant materials — ex vivoView study →Reference 5Kosmala M et al. · 2015AnimalChemical composition of defatted strawberry and raspberry seeds and the effect of these dietary ingredients on polyphenol metabolites, intestinal function and selected serum parameters — rat studyView study →Reference 6Milala J et al. · 2017AnimalEllagitannins from strawberries with different degrees of polymerization showed different metabolism through the gastrointestinal tract of ratsView study →}.

Castalagin is the predominant ellagitannin of oak-matured red wine, detectable as smooth astringency at 0.9–2.8 µmol/L, two to three orders of magnitude below the flavan-3-ol threshold of 600–1,000 µmol/L ^{7Reference 7Stark T et al. · 2010Matrix-calibrated LC-MS/MS quantitation and sensory evaluation of oak ellagitannins and their transformation products in red winesView study →}.

Protein precipitation is also the class basis for the tissue-tightening action attributed to tannin-rich plants generally; see tannins for the class picture.

Camu-camu is the herb that carries it.

Casuarinin binds and precipitates proteins, which probably explains several of the enzyme IC₅₀ values reported for it.

In a fungal system this shows up as anti-adhesion and as structural change, a denser mannan outer layer and reduced cell-wall porosity in Candida albicans, with polysaccharide and protein levels unaltered ^{12,13Reference 12Souza-Moreira TM et al. · 2013In vitroAnti-Candida targets and cytotoxicity of casuarinin isolated from Plinia cauliflora leaves in an in vitro studyView study →Reference 13Glasenapp Y et al. · 2019Anti-adhesion activity of tannins isolated from the mangrove Laguncularia racemosaView study →}.

On the one quantitative analysis of raspberry-leaf polyphenols, casuarinin rather than sanguiin H-6 is the largest single contributor to raspberry leaf’s astringency, at about 83% of identified phenolics in a leaf extract ^{14Reference 14Cyboran-Mikołajczyk S et al. · 2022Protection of erythrocytes and microvascular endothelial cells against oxidative damage by Fragaria vesca L. and Rubus idaeus L. leaves extracts — the mechanism of actionView study →}, and it runs at 34.8–117.9 mg/g of dry matter across 26 wild Rubus leaf samples ^{15Reference 15Oszmiański J et al. · 2015Determination of phenolic compounds and antioxidant activity in leaves from wild Rubus L. speciesView study →}.

Raspberry leaf, arjuna and haritaki carry it.

Punicalagin is a 1,085-dalton polyphenol with 17 free phenolic hydroxyls, concentrated at 1–2% of the dry weight of pomegranate peel ^{23Reference 23Fischer UA et al. · 2011Identification and quantification of phenolic compounds from pomegranate (Punica granatum L.) peel, mesocarp, aril and differently produced juices by HPLC-DAD-ESI/MSⁿView study →} and essentially absent from the arils ^{24Reference 24Gil MI et al. · 2000Antioxidant activity of pomegranate juice and its relationship with phenolic composition and processingView study →}, the classic distribution of a defensive protein-binding tannin in the barrier tissue.

Astringency, protein binding and metal chelation are one mechanism seen from three sides, and the same property underlies the traditional use of pomegranate rind as an antidiarrhoeal, the tannin-class reduction of non-haem iron absorption, and the molecule’s antimicrobial spectrum ^{25Reference 25Gosset-Erard C et al. · 2021Identification of punicalagin as the bioactive compound behind the antimicrobial activity of pomegranate (Punica granatum L.) peelsView study →}.

No molecular target is involved; this is physical chemistry.

Haritaki carries it.

Sanguiin H-6 is a 1,871 Da hydrolysable tannin carrying 52 oxygen atoms, and astringency is the direct physical consequence of that structure: multivalent phenolic hydroxyls hydrogen-bond and precipitate proteins, tightening mucosal surfaces.

It is the largest single polyphenol in raspberry and the dominant ellagitannin of Rubus generally ^{27,28Reference 27Mullen W et al. · 2002In vitroEllagitannins, flavonoids, and other phenolics in red raspberries and their contribution to antioxidant capacity and vasorelaxation properties — in vitroView study →Reference 28Gasperotti M et al. · 2010Profiling and accurate quantification of Rubus ellagitannins and ellagic acid conjugates using direct UPLC-Q-TOF HDMS and HPLC-DAD analysisView study →}, so where a Rubus leaf or fruit is used as an astringent this molecule is the principal thing doing it, despite the mechanism being class chemistry rather than a named receptor.

The astringency is luminal and topical by definition, since it happens where the tannin touches tissue, which is the only place the molecule ever is ^{29Reference 29González-Barrio R et al. · 2010Clinical trialBioavailability of anthocyanins and ellagitannins following consumption of raspberries by healthy human volunteers and subjects with an ileostomyView study →}.

No sanguiin-H-6-specific astringency measurement exists, and the assignment rests on class chemistry plus its documented abundance.

Raspberry leaf carries it.

Two galloyl esters plus a hexahydroxydiphenoyl bridge give a dense polyphenolic surface that hydrogen-bonds and hydrophobically complexes proteins, precipitating them, the defining behaviour of a hydrolysable tannin.

That single property is what disables bacterial surface proteins ^{30Reference 30Shiota S et al. · 2004Mechanisms of action of corilagin and tellimagrandin I that remarkably potentiate the activity of beta-lactams against methicillin-resistant Staphylococcus aureusView study →}, damages lipid bilayers ^{31,32Reference 31Coones RT et al. · 2024Interactions of galloylated polyphenols with a simple Gram-negative bacterial membrane lipid modelView study →Reference 32Funatogawa K et al. · 2004Antibacterial activity of hydrolyzable tannins derived from medicinal plants against Helicobacter pyloriView study →}, inhibits protein phosphatase-1 at sub-micromolar concentrations ^{33Reference 33Kónya Z et al. · 2019Inhibition of protein phosphatase-1 and -2A by ellagitannins — structure-inhibitory potency relationships and influences on cellular systemsView study →} and deters herbivores in the plant.

Synthesis of ring-expanded analogues showed that protein-precipitating capacity, redox activity and cytotoxicity can be tuned independently by changing the medium-ring size, direct evidence that the astringent behaviour is a structural property of the macrocycle rather than a by-product ^{34Reference 34Zheng S et al. · 2012Synthesis and biological profiling of tellimagrandin I and analogues reveals that the medium ring can significantly modulate biological activityView study →}.

Rose and meadowsweet carry it.

Three galloyl esters plus an HHDP bridge give a dense polyphenol surface that hydrogen-bonds and hydrophobically complexes proteins, precipitating salivary and mucosal proteins, the physical basis of astringency and of the tissue-tightening herbal action.

The same promiscuity is a liability elsewhere: eugeniin precipitates protein kinase A outright rather than inhibiting it selectively ^{35Reference 35Kosuge S et al. · 2001In vitroBiochemical characterization of galloyl pedunculagin (ellagitannin) as a selective inhibitor of the beta-regulatory subunit of A-kinase in vitroView study →}, so some reported enzyme inhibitions are complexation rather than active-site pharmacology.

Meadowsweet, clove, bearberry and peony carry it.

A monomeric hydrolysable tannin with one galloyl and two HHDP groups binds and precipitates proteins, which is what astringency is, and the same chemistry lies behind its antimicrobial MICs ^{8Reference 8Puljula E et al. · 2020In vitroAntimicrobial activities of ellagitannins against Clostridium perfringens, Escherichia coli, Lactobacillus plantarum and Staphylococcus aureus — in vitroView study →}, its digestive-enzyme inhibition ^{9,10Reference 9Toda M et al. · 2001In vitroInhibitory effects of ellagi- and gallotannins on rat intestinal α-glucosidase complexes — in vitroView study →Reference 10Sokolova E et al. · 2025In vitroInhibitory potential of sea buckthorn leaves extracts and its component casuarictin on pancreatic enzymes and LPS-induced TNF-α synthesis in human whole blood — in vitro / ex vivoView study →} and its documented stable 1:1 complex with rattlesnake secretory phospholipase A₂ (+937 Da confirmed by MALDI-TOF) ^{11Reference 11Rodrigues CFB et al. · 2019In vitroEvaluation of the inhibitory potential of casuarictin, an ellagitannin isolated from white mangrove (Laguncularia racemosa) leaves, on snake venom secretory phospholipase A2 — in vitro and mouseView study →}.

Binding avidity rises with molecular size, so casuarictin is at the weaker end of the ellagitannin range and its own oligomers bind harder.

The practical consequences for concentrated preparations are the usual ones, dryness and reduced absorption of non-haem iron, minerals and protein, none quantified for this molecule.

Clove, guava and raspberry leaf carry it.

Geraniin is a large hydrolysable tannin (about 953 Da, 27 oxygens) and carries the class’s defining physical mechanism: it binds and precipitates proteins and chelates metal ions, and the rambutan-peel phenolic fraction it dominates chelates Fe²⁺ and Cu²⁺ with EC₅₀ 0.80 and 0.13 mg/mL ^{16Reference 16Li Y et al. · 2018Metal chelating, inhibitory DNA damage, and anti-inflammatory activities of phenolics from rambutan (Nephelium lappaceum) peel and the quantifications of geraniin and corilaginView study →}.

This is the basis of the traditional antidiarrhoeal use of Geranium thunbergii (gennoshōko), the herb it is named for ^{17Reference 17Okuda T et al. · 1976Geraniin, a new ellagitannin from Geranium thunbergiiView study →}, and of the non-haem-iron absorption caution.

It is a physicochemical action rather than a receptor one, and it applies at the mucosal surface where geraniin actually is.

Chanca piedra and amla carry it.

Hamamelitannin precipitates surface proteins like any hydrolysable tannin, but it is a weak astringent relative to its own plant: two galloyls on a 484 Da branched sugar is a far smaller protein-binding surface than the bark’s polymeric proanthocyanidins (DP about 11–29, galloylated), which carry most of the tissue-tightening effect ^{18,19Reference 18Piazza S et al. · 2022In vitroAnti-inflammatory and anti-acne effects of Hamamelis virginiana bark in human keratinocytes — in vitroView study →Reference 19Touriño S et al. · 2008In vitroHighly galloylated tannin fractions from witch hazel (Hamamelis virginiana) bark: electron transfer capacity, in vitro antioxidant activity, and effects on skin-related cells — in vitroView study →}.

The herbal literature routinely credits hamamelitannin with witch hazel’s entire astringency, and that is a mis-attribution.

The steam-distilled witch hazel water most people buy contains essentially no tannin at all, so the retail product is not an astringent preparation in the pharmacological sense ^{18,20,21Reference 18Piazza S et al. · 2022In vitroAnti-inflammatory and anti-acne effects of Hamamelis virginiana bark in human keratinocytes — in vitroView study →Reference 20Wójciak M et al. · 2025ReviewHamamelis virginiana L. in skin care: a review of its pharmacological properties and cosmetological applications — reviewView study →Reference 21United States PharmacopeiaReviewWitch Hazel (Hamamelis Water) — official monographView study →}.

Witch hazel carries it.

Hydrolysable tannins bind and precipitate proteins non-specifically, and binding avidity scales with molecular size, so a 2,806-Da trimer carrying dozens of phenolic hydroxyls sits at the strong end of the class.

This is part of the mechanism behind raspberry-leaf astringency, and it is entirely a surface and luminal effect, the one that survives the absorption problem.

No protein-precipitation constant or salivary-protein-binding assay has been published for lambertianin C specifically, so the claim rests on hydrolysable-tannin class chemistry plus its measured abundance in the tissue, 57.1 mg/g dry weight in Rubus matsumuranus leaf, the most abundant compound of any class there ^{22Reference 22Kashchenko NI et al. · 2021Metabolites of Siberian raspberries — LC-MS profile, seasonal variation, antioxidant activity and thermal stability of Rubus matsumuranus phenolomeView study →}.

Raspberry leaf carries it.

As a hydrolysable tannin with multiple galloyl, HHDP and valoneoyl esters, rugosin A precipitates proteins, the physical basis of astringency and of the traditional astringent use of rose petal and meadowsweet flower.

The action follows from structure alone, with no dedicated rugosin A study behind it, so it is class-attributed rather than molecule-demonstrated.

The same complexation underlies the non-haem-iron-absorption caution.

Meadowsweet and rose carry it.

Rugosin D is a 1,875-dalton ellagitannin carrying two hexahydroxydiphenoyl groups and multiple galloyl esters, the classic multivalent surface that precipitates proteins, which is what astringency is.

That is a structural certainty rather than a measured finding for this molecule, since no protein-precipitation index or tannin-astringency assay has been published for rugosin D specifically.

It is a quantitatively major member of the astringent fraction in the plants it occurs in, up to 41 mg/g dry weight in mid-summer prickly-rose leaf against only 4 mg/g in the flower ^{26Reference 26Olennikov DN et al. · 2021Metabolites of prickly rose — chemodiversity and digestive-enzyme-inhibiting potential of Rosa acicularis and the main ellagitannin rugosin DView study →}, so in leaf preparations it is a substantial part of what the mouth registers.

Meadowsweet, rose and Rosa acicularis leaf carry it ^{26Reference 26Olennikov DN et al. · 2021Metabolites of prickly rose — chemodiversity and digestive-enzyme-inhibiting potential of Rosa acicularis and the main ellagitannin rugosin DView study →}.

Vescalagin is a 935-Da hydrolysable tannin with sixteen phenolic hydroxyls, so its astringency is the classic tannin mechanism of binding and precipitating salivary and mucosal proteins.

Unusually for this claim, it is quantified in humans: taste-dilution analysis identified vescalagin, castalagin, grandinin, the roburins and 33-deoxy-33-carboxyvescalagin as the key astringent molecules migrating from oak wood into bourbon whiskey and oak-matured red wine, and established human threshold concentrations and dose/response functions for them ^{36,37Reference 36Glabasnia A · 2006Sensory-directed identification of taste-active ellagitannins in American (Quercus alba L.) and European oak wood (Quercus robur L.) and quantitative analysis in bourbon whiskey and oak-matured red wines — human sensory panelView study →Reference 37Glabasnia A · 2007Identification and sensory evaluation of dehydro- and deoxy-ellagitannins formed upon toasting of oak wood (Quercus alba L.) — human sensory panelView study →}.

The human data are direct, though they are sensory rather than therapeutic.

Camu-camu carries it.