Quantitation and bitter taste contribution of saponins in fresh and cooked white asparagus (Asparagus officinalis L.)

A sensitive HPLC–MS/MS method was developed enabling the simultaneous quantification of bitter-tasting mono- and bidesmosidic saponins in fresh and processed asparagus (Asparagus officinalis L.). Based on quantitative data and bitter taste recognition thresholds, dose-over-threshold factors were determined for the first time to determine the bitter impact of the individual saponins. Although 3-O-[α-l-rhamnopyranosyl-(1 → 2)-α-l-rhamnopyranosyl-(1 → 4)-β-d-glucopyranosyl]-(25R/S)-spirost-5-ene-3β-ol was found based on dose-over-threshold factors to be the predominant bitter saponin in raw asparagus spears, 3-O-[α-l-rhamnopyranosyl-(1 → 2)-{α-l-rhamnopyranosyl-(1 → 4)}-β-d-glucopyranosyl]-26-O-[β-d-glucopyranosyl]-(25R)-22-hydroxyfurost-5-ene-3β,26-diol, 3-O-[α-l-rhamnopyranosyl-(1 → 2)-{α-l-rhamnopyranosyl-(1 → 4)}-β-d-glucopyranosyl]-26-O-[β-d-glucopyranosyl]-(25S)-22-hydroxyfurost-5-ene-3β,26-diol, and (25R)- and (25S)-furost-5-en-3β,22,26-triol-3-O-[α-l-rhamnopyranosyl-(1 → 4)-β-d-glucopyranoside]-26-O-β-d-glucopyranoside were found as key bitter contributors after cooking. Interestingly, the monodesmosidic saponins 5a/b were demonstrated for the first time to be the major contributor to the bitter taste of fresh asparagus spears, while the bidesmosides 1a/b and 2a/b may be considered the primary determinants for the bitter taste of cooked asparagus.