2,5-diketopiperazines
compound class / compound-diketopiperazines
2,5-ジケトピペラジン類
Cyclic dipeptides. Some of these present bitterness in roasted cacao.
On this page (6 sections)
Reading the bitterness
2,5-diketopiperazines are a group of cyclic dipeptides, and some of those found in roasted cacao present bitterness. A study combining quantitation, reconstitution, and omission tests with human dose-response found 7 bitter-tasting diketopiperazines to be the main sensory-active compounds in roasted cacao nibs.
A separate 2005 report identified 25 diketopiperazines from roasted cacao nibs, but only 5 had a dose-over-threshold (DoT) exceeding 1.0: cis-cyclo(L-Pro-L-Val), cis-cyclo(L-Val-L-Leu), cis-cyclo(L-Ala-L-Ile), cis-cyclo(L-Ala-L-Leu), and cis-cyclo(L-Ile-L-Pro). The remaining diketopiperazines existed below their own individual bitter thresholds, so the authors state there should be no contribution to cacao flavor. The compound class as a whole cannot be called bitter without qualification.
However, the authors explicitly note a limitation of the DoT metric itself: it does not account for the non-linear relationship between individual compound concentration and taste response. As a more accurate description, they separately report the human dose-response function for diketopiperazines. Ranking of the 5 compounds based only on DoT is constrained by this non-linearity.
In dichloromethane extracts of roasted cacao nibs, a group of diketopiperazines that elicit a blood-like, metallic-bitter taste sensation has been reported, with recognition thresholds for both metallic and bitter qualities determined separately. This sensation is attributed to the organic solvent extract and does not describe the nibs or chocolate as consumed; this distinction warrants attention.
Sources for this overview
Checked for this overview: Confirmed that 7 bitter diketopiperazines are main sensory-active compounds.
Checked for this overview: Confirmed the compound list of 5 out of 25 with DoT exceeding 1.0. / Confirmed the limitation of the DoT metric in not accounting for non-linearity. / Confirmed the metallic-bitter taste elicited by the extract and threshold determination by quality.
Follow the connections
2,5-diketopiperazines →contributes to→ bitterness →can be measured separately …→ astringency
Structured claims — open a section to read each claim's confidence, evidence and limits
Sensory (3)
Scope: A 2005 report identified 25 diketopiperazines, of which DoT > 1 in 5; a subsequent report shows contribution of 7 compounds.
Show data
compound-diketopiperazines —contribute_to→ sensation-bitterScope: Roasted cacao nibs analyzed by HPLC fractionation with sensory evaluation, LC-MS/MS, and chemical synthesis.
Note: Knowledge narrowing the compound class: the source states that the remaining diketopiperazines exist below their own individual bitter thresholds and therefore should not contribute to cacao flavor.
Show data
compound-diketopiperazines —has_dose_over_threshold_above_one_in_only→ "5 of 25 identified diketopiperazines: cis-cyclo(L-Pro-L-Val), cis-cyclo(L-Val-L-Leu), cis-cyclo(L-Ala-L-Ile), cis-cyclo(L-Ala-L-Leu), cis-cyclo(L-Ile-L-Pro)."Scope: Dichloromethane extracts of roasted cacao nibs.
Note: The sensory quality is described not as simple bitterness but as metallic-bitter taste. Recognition thresholds for the metallic quality and the bitter quality were determined separately.
Show data
compound-diketopiperazines —can_elicit→ "A blood-like, metallic-bitter taste sensation reported for dichloromethane extracts of roasted cacao nibs."