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. KeywordsAmino acids Kiln brown stain Kiln drying Maillard reaction Radiata pine Reducing sugars Sap Brought to you by |

Keywords ft a dint a pine Kiln brown stain Kiln drying Migration of water-soluble sugars Nitrogen containing compounds SummaryKiln drying of radiata pine (Pinus radiata D. Don) sapwood causes the formation of a brown discolouration, commonly called kiln brown stain. Kiln brown stain occurs just under (0.5-2mm) the wood surface but subsequent skim-dressing exposes the stain causing substantial economic loss in the New Zealand high-value lumber export markets. The present study quantified the changes in water-soluble compounds occurring at the wood surface and the centre of radiata pine sapwood boards (100 χ 40mm) during kiln drying at 90/6()°C and 120/7()°C. The results of the study showed that during kiln drying redistribution and concentration of water-soluble sugars and nitrogen containing compounds occur from the centre to the surface of radiata pine and this induces kiln brown stain. An Amadori-Maillard reaction is the likely cause of kiln brown stain formation in drying of radiata pine.

Nitrous acid deaminative depolymerisation was used to prepare three chitosan oligomer (CO) mixtures from high-molecular weight chitosan. These mixtures of chitosan oligosaccharides were analysed by electrospray ionisation mass spectroscopy, potentiometric titration and gel permeation chromatography. A method based on potentiometric titration of the amino groups of the oligomers gave an average degree of polymerisation (DP) for the three preparations of 5 (CODP5), 9 (CODP9) and 14 (CODP14). Chitosan acetate and the chitosan oligomer mixtures were assayed against Leptographium procerum, Sphaeropsis sapinea and Trichoderma harzianum on nutrient media. Leptographium procerum and S. sapinea growth was prevented by chitosan acetate and chitosan oligomers at concentrations of 0.3–0.4% (w/v), whereas T. harzianum was able to overcome the fungistatic action of these compounds. The oligomer preparation CODP14 exhibited superior specific activity to both CODP5 and chitosan acetate, suggesting an optimum molecular weight for bioactivity. All oligomer preparations were more effective at pH 4 than at pH 6. This result, in combination with the inactivity of N-acetylated CODP14, indicated that amino group protonation was an important factor for fungistatic activity. The CODP14 preparation was reduced with sodium borohydride and fractionated by alkali precipitation and ion exchange chromatography. Bioassays of these fractions pointed towards DP and degree of deacetylation (DD) as key factors in chito-oligosaccharide bioactivity. Conversely, the terminal aldehyde groups generated by depolymerisation did not contribute to the activity observed.

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