Isolation and Identification of Three γ-Glutamyl Tripeptides and Their Putative Production Mechanism in Aged Garlic Extract

J Agric Food Chem. 2018 Mar 21;66(11):2891-2899. doi: 10.1021/acs.jafc.7b05480. Epub 2018 Mar 8.


We analyzed aged garlic extract (AGE) to understand its complex sulfur chemistry using post-column high-performance liquid chromatography with an iodoplatinate reagent and liquid chromatography high resolution mass spectrometry (LC-MS). We observed unidentified peaks of putative sulfur compounds. Three compounds were isolated and identified as γ-glutamyl-γ-glutamyl- S-methylcysteine, γ-glutamyl-γ-glutamyl- S-allylcysteine (GGSAC) and γ-glutamyl-γ-glutamyl- S-1-propenyl-cysteine (GGS1PC) by nuclear magnetic resonance and LC-MS analysis based on comparisons with chemically synthesized reference compounds. GGSAC and GGS1PC were novel compounds. Trace amounts of these compounds were detected in raw garlic, but the contents of these compounds increased during the aging process. Production of these compounds was inhibited using a γ-glutamyl transpeptidase (GGT) inhibitor in the model reaction mixtures. These findings suggest that γ-glutamyl tripeptides in AGE are produced by GGT during the aging process.

Keywords: aged garlic extract; garlic; γ-glutamyl transpeptidase; γ-glutamyl tripeptide.

MeSH terms

  • Chromatography, High Pressure Liquid
  • Fruit / chemistry*
  • Fruit / growth & development
  • Garlic / chemistry
  • Garlic / growth & development*
  • Peptides / chemistry*
  • Peptides / isolation & purification
  • Plant Extracts / chemistry*
  • Plant Extracts / isolation & purification
  • Sulfur Compounds / chemistry
  • Sulfur Compounds / isolation & purification
  • Tandem Mass Spectrometry


  • Peptides
  • Plant Extracts
  • Sulfur Compounds