Synergistic effects of L-theanine on umami perception: A multimodal investigation integrating sensory evaluation, molecular docking and neurophysiological responses.

L-theanine in tea markedly enhances umami perception, but the mechanism remains insufficiently understood. This study aimed to investigate the umami perception mechanism of L-theanine and its synergistic effect with monosodium glutamate (MSG) through sensory evaluation, molecular simulation, and electroencephalogram (EEG) analysis. The threshold of L-Theanine is 0.2-0.95 g/100 mL and an equivalent umami intensity to 0.2 g/100 mL MSG at 4 g/100 mL. In L-theanine-MSG system, molecular-docking analyses revealed a markedly reduced binding free energy of -8.9 kcal/mol relative to either compound alone. This cooperative interaction is stabilized by an extended hydrogen-bonding network (SER-148, THR-149, ALA-170, SER-276 and SER-107) and reinforced by salt-bridge formation with the cationic residues ARG-151 and ARG-277. EEG results further substantiated this synergy. L-theanine recruited the occipital lobe and generated greater inter-individual discriminability between high- and low-umami-sensitivity cohorts. This study provides novel insights into tea's umami modulation and paves the way for advancing natural flavor enhancement.