Abstract
The aim of this work was to determine the structural characteristics of the condensed tannins isolated from the aqueous extract of black spruce (Picea mariana Mill) bark. This is the first report on the structural characterization of condensed tannins from black spruce bark. The condensed tannins from the hot water extract prepared from Picea mariana bark were isolated by column chromatography on Sephadex LH-20 media. In this study, UV-visible and 13C-NMR spectroscopic techniques, along with pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and liquid chromatogramphy analyses were applied to determine the structural characteristics of black spruce bark tannins. We have confirmed for the first time the presence of methoxylated B-rings in the flavanol units of condensed tannins from black spruce bark, which could be regarded as further contribution to the chemotaxonomy of the genus Picea. The methoxylation of Norway spruce bark condensed tannins have been demonstrated previously.
Highlights
In the wood industry, large amounts of bark waste are produced
A maximum at 549 nm, observed in Condensed Tannins (CT) spectrum obtained in our research, indicates that the condensed tannins from black spruce bark are mainly PC rather than PD. 3.2. 13C-NMR Analysis The chemical characterization of the purified CT extracted from black spruce bark was initiated by 13C-NMR analysis, mainly with an aim to determine their degree of polymerization
Since the typical chemical signal for the C3’ and the C5’ of PD units is not detected, it can be concluded that the condensed tannins from hot water extract of black spruce bark are exclusively composed of PC units
Summary
Large amounts of bark waste are produced. This waste material is mostly used in energy production and is burned in large furnaces. Barks of several tree species are known to contain bioactive chemicals, such as the proanthocyanidins, which are known as condensed tanins and belong to the group of polymer polyphenols. The isolation and utilization of various polyphenols from bark, including polymer proanthocyanidins, could add value to the transformation of bark presently used solely as energy resource. Proanthocyanidins (PAs) can be classified as oligomers (dimers to pentamers) and polymers (hexamers and higher, known as condensed tannins, CT) of flavan-3-ol monomer units most frequently linked through either C4/C6 or C4/C8 C-C bonds (Figure 1). The most common classes are procyanidins consisting of catechin, epicatechin and/or their galloylated derivatives, and prodel-
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