Decoding bitter peptides in soy sauce: From identification to mechanism in bitter taste formation.

The molecular basis of bitterness in soy sauce was investigated through an integrated approach combining peptidomics, sensory evaluation, cell biology, and molecular docking. Ethanol-extracted bitter peptides (BPs) were identified via liquid chromatography-tandem mass spectrometry. Seventeen BP candidates were shortlisted based on toxicity, allergenicity, bitterness predictions and hydrophobicity calculation. Sensory evaluation showed that 13 peptides exhibited bitterness, with 8 significantly enhancing bitterness of 6 key free amino acids in soy sauce. Using a HEK-293T cell-based cAMP assay, FYL and VLY were identified as hTAS2R4 ligands (EC₅₀ = 62.11 and 199.51 μM, respectively). Molecular docking revealed that both peptides bind primarily via hydrophobic interactions to residues such as VAL85, PHE88, and PHE62. These findings provide a theoretical basis for bitterness mechanism and flavor improvement of soy sauce.