Identification of mozambioside roasting products and their bitter taste receptor activation

Arabica coffee contains the bitter-tasting diterpene glycoside mozambioside, which degrades during coffee roasting, leading to yet unknown structurally related degradation products with possibly similar bitter-receptor-activating properties. The study aimed at the generation, isolation, and structure elucidation of individual pyrolysis products of mozambioside and characterization of bitter receptor activation by in vitro analysis in HEK 293T-Gα16gust44 cells. The new compounds 17-O-β-D-glucosyl-11-hydroxycafestol-2-on, 11-O-β-D-glucosyl-16-desoxycafestol-2-on, 11-O-β-D-glucosyl-(S)-16-desoxy-17-oxocafestol-2-on, 11-O-β-D-glucosyl-15,16-dehydrocafestol-2-on, and 11-O-β-D-glucosyl-(R)-16-desoxy-17-oxocafestol-2-on were isolated from pyrolyzed mozambioside by HPLC and identified by NMR and UHPLC-ToF-MS. Roasting products 11-O-β-D-glucosyl-(S)-16-desoxy-17-oxocafestol-2-on, 11-O-β-D-glucosyl-15,16-dehydrocafestol-2-on, and 11-O-β-D-glucosyl-(R)-16-desoxy-17-oxocafestol-2-on had lower bitter receptor activation thresholds compared to mozambioside. Molecular docking simulations revealed the binding modes of the compounds 11-O-β-D-glucosyl-15,16-dehydrocafestol-2-on and 11-O-β-D-glucosyl-(R)-16-desoxy-17-oxocafestol-2-on and their aglycone 11-hydroxycafestol-2-on in the two cognate receptors TAS2R43 and TAS2R46. The newly discovered roasting products 17-O-β-D-glucosyl-11-hydroxycafestol-2-on, 11-O-β-D-glucosyl-(S)-16-desoxy-17-oxocafestol-2-on, 11-O-β-D-glucosyl-15,16-dehydrocafestol-2-on, and 11-O-β-D-glucosyl-(R)-16-desoxy-17-oxocafestol-2-on were detected in authentic roast coffee brew by UHPLC-ToF-MS and could contribute to coffee's bitter taste impression.