Herbal Bitters

Cynaropicrin is the defining bitter principle of artichoke; it carries about 80% of the plant’s characteristic bitterness, and no other artichoke constituent comes close ^{4Reference 4Eljounaidi K et al. · 2015Accumulation of cynaropicrin in globe artichoke and localization of enzymes involved in its biosynthesisView study →}.

Sensory-panel structure–activity work localises the bitterness to the α-methylene-γ-lactone: derivatisation that removes the exomethylenes or opens the lactone ring abolishes it ^{5,6Reference 5Cravotto G et al. · 2005Chemical and biological modification of cynaropicrin and grosheimin: a structure-bitterness relationship study — sensory panel evaluation of derivativesView study →Reference 6Scotti L et al. · 2007Quantitative elucidation of the structure-bitterness relationship of cynaropicrin and grosheimin derivativesView study →}.

Human bitter perception of this chemotype runs through TAS2R46, the bitter GPCR deorphanised as broadly tuned to sesquiterpene lactones, with edible-Asteraceae lactones giving low-micromolar EC50s there ^{7,8,9Reference 7Brockhoff A et al. · 2007In vitroBroad tuning of the human bitter taste receptor hTAS2R46 to various sesquiterpene lactones, clerodane and labdane diterpenoids, strychnine, and denatonium — in vitro receptor assayView study →Reference 8Yanagisawa T · 2021In vitroCharacterization of the human bitter taste receptor response to sesquiterpene lactones from edible Asteraceae species and suppression of bitterness through pH control — in vitroView study →Reference 9Salamone S et al. · 2026In vitroDietary terpenoid lactones are promiscuous agonists of bitter taste receptors (TAS2Rs) — in vitroView study →}.

Downstream, oral artichoke leaf extract (1% cynaropicrin) raised gastric juice volume and mucus in rats, and cynaropicrin alone at one-hundredth the extract dose reproduced the gastroprotection while chlorogenic acid did not ^{10Reference 10Ishida K et al. · 2010AnimalEffects of artichoke leaf extract on acute gastric mucosal injury in ratsView study →}.

Cynaropicrin itself has never been assayed at a named TAS2R, so the receptor step is class inference, and the secretory chain is rodent-only.

Found in artichoke.

Taraxinic acid glucoside is the structurally defined bitter principle of common dandelion: the quantitatively dominant sesquiterpene lactone of both latex (up to 7% of latex fresh weight, main root) and the leaf lactone fraction ^{15,16Reference 15Huber M et al. · 2015Identification, quantification, spatiotemporal distribution and genetic variation of major latex secondary metabolites in the common dandelion (Taraxacum officinale agg.)View study →Reference 16Esatbeyoglu T et al. · 2017Sesquiterpene lactone composition and cellular Nrf2 induction of Taraxacum officinale leaves and roots and taraxinic acid β-D-glucopyranosyl esterView study →}, and the molecule the nineteenth-century collective name “taraxacin” was reaching for, since no primary isolation of taraxacin from T. officinale exists ^{17Reference 17Ahmad VU et al. · 2000Taraxacin, a new guaianolide from Taraxacum wallichiiView study →}.

Genus reviews assign dandelion’s bitterness, and its traditional dyspepsia, appetite and choleretic use, to this lactone fraction with taraxinic acid derivatives as its principal members ^{18,19Reference 18Schütz K et al. · 2006ReviewTaraxacum — a review on its phytochemical and pharmacological profileView study →Reference 19Sharifi-Rad M et al. · 2018Ethnobotany of the genus Taraxacum — phytochemicals and antimicrobial activityView study →}.

The molecule has never been assayed at any bitter taste receptor; the mechanism is class inference, since hTAS2R46 was deorphanised as broadly tuned to sesquiterpene lactones using herbolide D rather than this compound ^{7Reference 7Brockhoff A et al. · 2007In vitroBroad tuning of the human bitter taste receptor hTAS2R46 to various sesquiterpene lactones, clerodane and labdane diterpenoids, strychnine, and denatonium — in vitro receptor assayView study →}, and the lactone ring functions as a general bitter chemotype across several TAS2Rs ^{9Reference 9Salamone S et al. · 2026In vitroDietary terpenoid lactones are promiscuous agonists of bitter taste receptors (TAS2Rs) — in vitroView study →}.

The bitterness pharmacophore and the thiol-alkylating warhead are the same structural feature, the α-methylene-γ-lactone.

The one mammalian secretory measurement is negative: 70 mg/kg i.v. did not alter histamine-stimulated gastric acid secretion in the lumen-perfused rat stomach ^{20Reference 20Wu SH et al. · 2002Wu SH, et al. (2002). [Anti-gastric ulcer sesquiterpene lactone glycosides from Crepis napifera]. Yao Xue Xue Bao. https://pubmed.ncbi.nlm.nih.gov/12579896/View study →}, so the bitters-to-secretion chain is unsupported for this molecule specifically, and it is not counted as choleretic.

Found in dandelion.

The bitter-taste receptors TAS2R43 and TAS2R46 are “exquisitely sensitive to lactucin, lactucopicrin, and 11β,13-dihydrolactucin”, with thresholds for this compound of 10 µM (TAS2R43) and 30 µM (TAS2R46); the same work quantified it across chicory, radicchio and roasted-chicory surrogate coffee and ran a human sensory panel showing that consumption order changes perceived bitterness ^{1Reference 1Lang R et al. · 2022In vitroOverlapping activation pattern of bitter taste receptors affect sensory adaptation and food perception — in vitro receptor assays plus human sensory panelView study →}.

It is an unusually well-resolved interaction with a named human protein for a phytochemical.

The authors note the compound’s concentration in surrogate-coffee brew sits below the receptor thresholds, so its own contribution to that drink’s bitterness is limited, and no extra-oral TAS2R effect on gut, airway, appetite or digestive secretion has been tested for this molecule, so any bitter-tonic framing is an inference from class behaviour.

Found in chicory root and roasted-chicory coffee substitute ^{1Reference 1Lang R et al. · 2022In vitroOverlapping activation pattern of bitter taste receptors affect sensory adaptation and food perception — in vitro receptor assays plus human sensory panelView study →}, radicchio ^{1Reference 1Lang R et al. · 2022In vitroOverlapping activation pattern of bitter taste receptors affect sensory adaptation and food perception — in vitro receptor assays plus human sensory panelView study →} and lettuce ^{1,2,3Reference 1Lang R et al. · 2022In vitroOverlapping activation pattern of bitter taste receptors affect sensory adaptation and food perception — in vitro receptor assays plus human sensory panelView study →Reference 2Mai F · 2016Structural and sensory characterization of novel sesquiterpene lactones from iceberg lettuceView study →Reference 3Stojanović M et al. · 2025Phytochemical composition and overall taste modulation in lettuce: combination of cultivar and biofertiliserView study →}.

Lactucopicrin is one of the two principal bitter guaianolides of chicory and of lactucarium, and its bitterness has unusually strong real-world validation.

It was the major sesquiterpene lactone of fresh-cut witloof chicory immediately after processing, and warm-water washing that removed 60.9–64.5% of total lactones reduced perceived bitterness in parallel ^{11Reference 11Wulfkuehler S et al. · 2013Sesquiterpene lactone content and overall quality of fresh-cut witloof chicory (Cichorium intybus L. var. foliosum Hegi) as affected by different washing proceduresView study →}.

A 13-genotype field panel produced a bitterness scale correlating lactone content with panel-perceived bitterness, and CRISPR knockouts of CiGAS and CiGAO moved edited lines down it, some losing perceptible bitterness entirely ^{12Reference 12Domont J et al. · 2023CRISPR/Cas9-targeted mutagenesis of CiGAS and CiGAO to reduce bitterness in chicory (Cichorium intybus L.)View study →}.

In forage agronomy, ruminant refusal tracks lactone content: the West Virginia herbage carrying more than twice the lactucopicrin of the Pennsylvania herbage was the one cattle would not graze ^{13Reference 13Foster JG et al. · 2006Influence of cultivation site on sesquiterpene lactone composition of forage chicory (Cichorium intybus L.)View study →}.

Every result is for the lactone fraction rather than this molecule alone (lactucin is present at about five times the level in lettuce extract ^{14Reference 14Kim HW et al. · 2019AnimalEffectiveness of the sleep enhancement by green romaine lettuce (Lactuca sativa) in a rodent model — animal in vivoView study →}), lactucopicrin has never been assayed at a named human TAS2R, and the downstream bitter-tonic sequence of salivation, gastric acid and bile has not been measured for it; the receptor step is class inference from a well-matched chemotype.

Found in wild lettuce.