LC-HRMS-based identification and quantification of novel 2,5-diketopiperazines in roasted coffee

Area of Science:

• Food Chemistry
• Analytical Chemistry
• Organic Chemistry

Background:

• 2,5-Diketopiperazines (DKPs) are cyclic dipeptides formed from amino acids.
• DKPs are known contributors to the characteristic bitterness in roasted foods, notably coffee.
• Understanding DKP profiles is crucial for food quality and sensory analysis.

Purpose of the Study:

• To identify and quantify novel DKPs in coffee samples using advanced analytical techniques.
• To develop and validate a quantitative method for DKP analysis in various coffee matrices.
• To investigate the relationship between DKP concentrations and coffee roasting conditions.

Main Methods:

• Liquid chromatography-high resolution mass spectrometry (LC-HRMS) was employed for DKP identification and quantification.
• Electron-spray ionization tandem mass spectrometry (ESI-MS/MS) in positive-ion mode was used for structural elucidation.
• Quantitative analysis was performed using authentic standards in powdered coffee and aqueous infusions.

Main Results:

• A total of 33 DKPs were identified, with 23 reported as novel compounds.
• Bicyclic forms of DKPs containing polar residues like glutamic acid and lysine were detected.
• Cyclo(Pro-Leu), cyclo(Pro-Val), and cyclo(Pro-Tyr) were the most abundant DKPs, with concentrations varying by roasting conditions.

Conclusions:

• LC-HRMS is effective for identifying and quantifying DKPs in coffee.
• The identified DKP concentrations in coffee infusions align with reported bitterness thresholds.
• This study provides valuable insights into DKP formation and presence in coffee, impacting flavor profiles.