Structural and sensory characterization of bitter tasting steroidal saponins from asparagus spears (Asparagus officinalis L.)

Application of sequential solvent extraction and iterative chromatographic separation in combination with taste dilution analysis recently revealed a series of steroidal saponins as the key contributors to the typical bitter taste of white asparagus spears (Asparagus officinalis L.). Besides six previously reported saponins, (25R)-furost-5-en-3β,22,26-triol-3-O-[α-l- rhamnopyranosyl-(1→4)-β-d-glucopyranoside]-26-O-β-d- glucopyranoside, (25R)-furostane-3β,22,26-triol-3-O-[α-L- rhamnopyranosyl-(1→4)-β-d-glucopyranoside]-26-O-β-d- glucopyranoside, and (25S)-furostane-3β,22,26-triol-3-O-[α-l- rhamnopyranosyl-(1→4)-β-d-glucopyranoside]-26-O-β-d- glucopyranoside, and 3-O-[{α-l-rhamnopyranosyl-(1→2)}{α-l- rhamnopyranosyl-(1→4)}-β-d-glucopyranosyl]-(25S)-spirost-5-ene- 3β-ol were identified for the first time as key bitter compounds in the edible spears of white asparagus by means of LC-MS/MS, LC-TOF-MS, 1D/2D-NMR spectroscopy, and hydrolysis experiments. This paper presents the isolation, structure determination, and sensory activity of these saponins. Depending on their chemical structure, the saponins identified showed human bitter recognition thresholds between 10.9 and 199.7 μmol/L (water).