Insights into the taste of organic acids via TAS1Rs

Organic acids contribute significantly to the flavor of fermented foods by imparting sourness. Although mice generally avoid sour taste, previous studies have reported greater consumption of l-lactic acid than its d-enantiomer, suggesting enantiomer-specific recognition. This behavior is hypothesized to involve TAS1Rs, which consists of sweet/umami receptors. However, it remains unclear whether TAS1Rs additionally contribute to the recognition of other chiral organic acids. This study aimed to evaluate the role of TAS1Rs, particularly TAS1R3, in the modulation of enantiomer-dependent behavioral responses to organic acids in mice.

Behavioral responses were evaluated using 48-h and 1-h 2-bottle tests. Binding of organic acids to TAS1Rs was investigated by differential scanning fluorimetry (DSF) with the ligand-binding domain (LBD) of medaka Tas1r2a/Tas1r3.

Wild-type mice consumed more d-malic acid than l-malic acid in the 48-h test, whereas Tas1r3-KO mice showed no such difference. This pattern was not observed in the short-term 1-h test, which minimized the contribution of post-ingestion and learned effects. DSF analysis revealed no binding of any of the tested organic acids to the LBD of medaka Tas1r2a/Tas1r3.

Organic acids may elicit TAS1R3-dependent post-ingestion signals that contribute to enantiomer-selective consumption in mice. Electrostatic interactions and hydrogen-bonding networks within the orthosteric pocket of TAS1Rs may account for the differences in binding affinity to the LBD of medaka Tas1r2a/Tas1r3 between organic acids and L-alanine, a known ligand.