lactucin

Lactucin is one of the sesquiterpene lactones (a group of compounds often possessing bitterness, with cyclic lactone structures derived from terpenes) found in chicory. In a receptor assay using cultured cells, lactucin activated one bitter taste receptor, TAS2R43, with a detection threshold of 10 µM and an EC50 (the concentration at which response reaches half-maximal) of 14.9 +/- 2.5 µM, and also activated another receptor, TAS2R46, with an EC50 of 8.85 +/- 1.17 µM. Lactucopicrin, also examined in the same assay, activated TAS2R43 at lower concentrations (detection threshold 0.1 µM, EC50 0.46 +/- 0.08 µM); the paper ranked lactucopicrin as the strongest, lactucin as moderate, and 11β,13-dihydrolactucin as the weakest.

Raw chicory roots contained lactucin at a concentration of 42.13 +/- 4.10 µM per 1 gram, roasted chicory coffee substitute powder at 32.48 +/- 5.87 µM, and extract at 1.35 +/- 0.10 µM. This concentration in the extract is approximately one order of magnitude lower than the EC50 value needed to activate the receptor, and the bitterness of the beverage cannot be attributed solely to lactucin's receptor action. Furthermore, the TAS2R43 gene copy number varies from 0 to 2 copies among individuals; in a survey of 946 people from 52 worldwide populations, the deletion genotype reached a global frequency of 0.33, and in Europe, more than 20% of subjects lacked this gene. The potency ranking measured in cell assays cannot be treated directly as a universal ranking of bitterness intensity across all populations.

The amount of sesquiterpene lactones in chicory is not a fixed property of the ingredient but changes substantially with processing. In a washing experiment using fresh-market chicory (witloof), all washing methods significantly reduced both the total sesquiterpene lactone content and bitterness; warm-water washing reduced the total by approximately 60.9–64.5%. It has also been documented that as storage progresses, the proportion of a related compound, 11(S),13-dihydrolactucin, increases. Although this study does not report lactucin concentration specifically, it supports that the amount of chicory's bitter compounds varies with cooking and storage conditions.