Salinity-dependent changes in Retronasal detection and dose-over-threshold of kokumi peptides in fermented soybean paste

Kokumi is a taste-enhancing sensation that adds complexity, mouthfulness, and continuity by modulating basic taste perceptions. γ-Glutamyl peptides, abundant in fermented foods, are known kokumi-active compounds. This study examined how salinity influences retronasal detection thresholds and dose-over-threshold (DoT) values of nine γ-glutamyl peptides commonly found in fermented soybean paste (doenjang). Most peptides showed higher best estimate threshold (BET) values as salinity increased, indicating reduced retronasal detectability. However, γ-Glu-Phe (γ-EF) showed decreasing thresholds and consistently maintained a DoT >1 across all salinity levels, suggesting stable, salt-resistant kokumi activity. To explore underlying mechanisms, p K a values of selected peptides were measured under different salinity conditions. No significant or consistent shifts were observed, indicating salinity's effect may not be related to ionization but rather to receptor-level interactions. Overall, γ-EF was identified as a key kokumi-active peptide in doenjang, and findings offer insights for improving kokumi flavor in fermented foods with reduced or varying salt levels.