Armando G. McDonald, Marc Fernandez, Bernhard Kreber, Frank Laytner
The Chemical Nature of Kiln Brown Stain in Radiata Pine
Summary
This paper presents results of a study on the chemical nature of kiln brown stain (KBS) that develops in
kiln dried radiata pine (Pinus radiata D. Don) sapwood. KBS is a chocolate brown discolouration which
develops approximately 0.5 mm under the timber surface. Stain free radiata pine was achieved during
drying trials on “green” radiata pine sapwood which had been treated to extensive cold and hot water
extraction. Differences in chemical composition between the sap and hot water extract were observed.
Chemical analyses (of the water-soluble extracts) by a combination of chromatographic and spectroscopic
techniques, demonstrated that carbohydrates, cyclitols, amino acids, protein, and phenolics were
the main compound classes present. The presence of reducing sugars (glucose and fructose) and amino
acids (glutamic acid) in the sap and hot water extracts support the theory that Amadori-Maillard type
reactions significantly contribute to the formation of colour in KBS. Furthermore, lignin was also detected
and is suspected to contribute to KBS formation. The relative contributions of colour formation to
KBS intensity from either phenolics or Maillard-Amadori mechanisms is unknown.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 54, 01/2000
Pages: 12 - 22
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