Investigating the bitterness of flavonoids in <i>Oroxylum indicum</i> : receptors, affinities, mechanism, and contribution

Abstract Although Oroxylum indicum is a widely consumed herb with many pharmaceutical qualities, no study has investigated its sensory properties, especially the bitterness. To thoroughly understand the bitter taste, we conducted machine learning (BitterX) screening of bitter taste receptors for beneficial flavonoids in the fruits, explored the interactions through molecular docking, and performed chemical quantification with electronic tongue analysis to determine the compounds contributing to the overall bitterness. The main flavonoids were found to bind to five bitter taste receptors with high predicted scores and low binding affinities, including TAS2R5, TAS2R7, TAS2R14, TAS2R39, and TAS2R43. Through multivariate data analysis, baicalein, baicalin, chrysin, oroxin A, oroxin B, and chrysin-7-O-glucuronide were highly correlated with the overall bitterness, ranging from R = 0.83 to 0.92. These compounds were present more in the seeds, making them more bitter than the coats. The principal component analysis biplot also indicated that saltiness could possibly mask the bitterness of O. indicum.