Discolouration of birch wood: analysis of extractives from discoloured surface of vacuum-dried European white birch (Betula pubescens) board |
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Authors: | Eveliina Hiltunen Kirsi Mononen Leila Alvila Tuula T Pakkanen |
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Institution: | (1) Department of Chemistry, University of Joensuu, P.O. Box 111, 80101 Joensuu, Finland |
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Abstract: | A discolouration that appeared on the surfaces of a European white birch (Betula pubescens) board during vacuum drying was studied by means of colour measurements (CIEL*a*b*), elemental analysis and the analysis of extractives. The discoloured surface layer of the dried board contained substantially
more methanol-soluble extractives than did the light-coloured part (50.7 mg g−1 vs. 26.7 mg g−1 dry wood), and the colour difference (ΔE*
ab
20.0) between the two extracts was notable. Characterization by means of GC and 13C NMR spectroscopy showed that the extracts contain sugars (mainly glucose and fructose), low-molecular-weight phenolic compounds,
proanthocyanidins, Brauns’ lignin and fatty acid esters. Concentrations of sugars, low-molecular-weight phenols, proanthocyanidins
and Brauns’ lignin were higher in the discoloured surface layer than in the light-coloured part. The yellowness of the surface
layer was associated with the accumulation of low-molecular-weight phenolic extractives, and the redness with Brauns’ lignin
and possibly proanthocyanidins. |
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Keywords: | |
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