Twenty-four plant lignans were analyzed by high-performance liquid chromatography-tandem mass spectrometry in bran extracts of 16 cereal species, in four nut species, and in two oilseed species (sesame seeds and linseeds). Eighteen of these were lignans previously unidentified in these species, and of these, 16 were identified in the analyzed samples. Four different extraction methods were applied as follows: alkaline extraction, mild acid extraction, a combination of alkaline and mild acid extraction, or accelerated solvent extraction. The extraction method was of great importance for the lignan yield. 7-Hydroxymatairesinol, which has not previously been detected in cereals because of destructive extraction methods, was the dominant lignan in wheat, triticale, oat, barley, millet, corn bran, and amaranth whole grain. Syringaresinol was the other dominant cereal lignan. Wheat and rye bran had the highest lignan content of all cereals; however, linseeds and sesame seeds were by far the most lignan-rich of the studied species.
Summary
The hydrophilic and lipophilic extractives in the heartwood of knots from 7 Norway spruce trees
were analysed by GC, GC-MS and HPSEC. The knots contained extremely large amounts of lignans,
6–24% (w/w), with hydroxymatairesinol comprising 65–85% of the lignans. Even the knots
of the young trees contained 4–8% (w/w) of lignans. The variation in the amount of lignans was
large among knots, both within a single tree and between trees. In addition to the lignans, knots
also contained 2–6% (w/w) of a complex mixture of lignan-like compounds with 3, 4 and even up
to 6 phenyl propane units, here called oligolignans. The amounts of lignans in the knots were similar
in the radial direction from the pith into the outer branch, but decreased dramatically outwards
in the branch, almost disappearing after 10–20 cm. The ratio of the 2 epimers of hydroxymatairesinol
differed between different knots and even within the knot. A new spruce lignan, nortrachelogenin,
or its enantiomer, wikstromol, was detected in knots from trees in northern Finland
as opposed to samples from southern Finland. The amount of lipophilic extractives was small compared
to the amount of hydrophilic extractives in the knots. Five of the dead knots contained more
resin acids and free diterpenyl alcohols than ordinary stemwood. In the other knots, the amount of
lipophilic extractives was on the same level as stem heartwood. The stem sapwood contained larger
amounts of esterified fatty acids than the knots.
The antioxidant potency and the radical scavenging capacity of superoxide and peroxyl radicals were assessed for 13 hydrophilic knotwood extracts of commercially important wood species, or fractions thereof, as well as for five pure wood-derived lignans and the flavonoid taxifolin. The chemical composition of the knotwood extracts was determined by gas chromatography combined with mass spectrometry. Most of the investigated wood species were rich in hydrophilic extractives (10-20% of the dry wood) with one or a few compounds dominating in each extract. All extracts had a high antioxidative potency and/or radical scavenging capacity as compared to the well-known antioxidants Trolox and butylated hydroxyanisole. The pure wood-derived lignans and taxifolin also had a high antioxidative potency and/or radical scavenging capacity. However, the antioxidant potency and/or radical scavenging capacity of several of the hydrophilic knotwood extracts were higher than that of the dominating compounds in pure form.
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