Sensory-directed fractionation of extracts prepared from oat flour (Avena sativa L.) followed by LC-TOF-MS, LC-MS/MS, and 1D/2D-NMR experiments revealed avenanthramides and saponins as the key phytochemicals contributing to the typical astringent and bitter off-taste of oat. Besides avenacosides A and B, two previously unreported bitter-tasting bidesmosidic saponins were identified, namely, 3-(O-α-l-rhamnopyranosyl(1→2)-[β-d-glucopyranosyl(1→3)-β-d-glucopyranosyl(1→4)]-β-d-glucopyranosid)-26-O-β-d-glucopyranosyl-(25R)-furost-5-ene-3β,22,26-triol, and 3-(O-α-l-rhamnopyranosyl(1→2)-[β-d-glucopyranosyl(1→4)]-β-d-glucopyranosid)-26-O-β-d-glucopyranosyl-(25R)-furost-5-ene-3β,22,26-triol. Depending on the chemical structure of the saponins and avenanthramides, sensory studies revealed human orosensory recognition thresholds of these phytochemicals to range between 3 and 170 μmol/L.
A total of 59 taste-active molecules
were quantitated and then
rated for their individual taste impact on the basis of dose-over-threshold
factors in oat flour (Avena sativa L.).
A sensitive high-performance liquid chromatography–tandem mass
spectrometry method was developed to quantitate bitter-tasting steroidal
and furostanol saponins as well as avenanthramides. Four monoglycerides,
five free fatty acids and four saponins were confirmed for the first
time to be major contributors to the bitter off-taste of oats, among
them 1-linoleoyl-rac-glycerol, 1-stearoyl-rac-glycerol, 1-oleoyl-rac-glycerol, 1-palmitoyl-rac-glycerol, linoleic acid, linolenic acid, oleic acid,
palmitic acid, and stearic acid as well as avenacosides A and B and
the recently identified furostanosides 3-(O-α-l-rhamnopyranosyl(1→2)-[β-d-glucopyranosyl(1→3)-β-d-glucopyranosyl(1→4)]-β-d-glucopyranosid)-26-O-β-d-glucopyranosyl-(25R)-furost-5-ene-3β,22,26-triol and 3-(O-α-l-rhamnopyranosyl(1→2)-[β-d-glucopyranosyl(1→4)]-β-d-glucopyranosid)-26-O-β-d-glucopyranosyl-(25R)-furost-5-ene-3β,22,26-triol. By means of a stable
isotope dilution assay, quantitated avenanthramides 2c, 2p, 2f, 1p,
1c, 1f, and 3f were found in concentrations below their thresholds
and, therefore, did not contribute to the bitter sensation of the
tested oat flour.
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