Kokumi and CaSR
Kokumi is a relatively recently characterized flavor quality — sometimes described as 'richness', 'mouthfulness', or 'continuity'. Unlike the basic tastes it doesn't add flavor of its own, but amplifies and prolongs the perception of sweet, salty, and umami signals. It's mediated by the calcium-sensing receptor (CaSR), a Class C GPCR expressed on Type I taste cells.
CaSR and γ-Glutamyl Peptides
Glutathione (γ-Glu-Cys-Gly) and other γ-glutamyl peptides are the primary CaSR ligands in food. They're found in high concentrations in aged cheeses, fish sauce, yeast extract, and long-simmered stocks — foods widely perceived as having unusual depth and persistence. CaSR activation extends the duration and intensity of co-presented taste stimuli without adding a distinct taste of its own.
Engineering Strategy
Increasing γ-Glu-peptide content in a crop requires overexpressing γ-glutamyltranspeptidase (GGT) — the enzyme that catalyzes the transfer of γ-glutamyl groups to amino acid acceptors. Alternatively, engineering glutathione biosynthesis (γ-glutamylcysteine synthetase and glutathione synthetase) increases the substrate pool from which kokumi-active peptides are derived. The IFI-K axis scores CaSR activation from construct-modified tissue extracts.