ISPM-15 HEAT-TREATMENT INDUCED CHANGES IN EXTRACTIVES OF SCOTS PINE AND THE EFFECT ON FUNGAL DISCOLORATION

Gerda LAMBERTZ
Dr.eng. - Johann Heinrich von Thuenen-Institute (vTI), Federal Research Institute for Rural Areas, Forestry and Fisheries, Institute of Wood Technology and Wood Biology (HTB)
Address: Leuschnerstrasse 91, 21031 Hamburg, Germany
E-mail: gerda.lambertz@vti.bund.de

Johannes WELLING
Dr.eng. - Johann Heinrich von Thuenen-Institute (vTI), Federal Research Institute for Rural Areas, Forestry and Fisheries, Institute of Wood Technology and Wood Biology (HTB)
Address: Leuschnerstrasse 91, 21031 Hamburg, Germany
E-mail: johannes.welling@vti.bund.de

Abstract: According to the International Standard of Phytosanitary Measures (ISPM No 15), heat treatment is one of the most important methods in order to avoid the spreading of harmful quarantine organisms like insects and nematodes when using wood-packaging material. The standard defines heat treatment at 56°C core temperature for at least 30 minutes without referring neither to the moisture content of the wood nor to the presence of fungi after the treatment. Under these conditions, i.e. a pure heat treatment without technical drying, the moisture content of the wood is not decreased. In consequence, it is a common problem that particularly fresh sapwood shows a great affinity to mould and blue stain. The infestation is much higher compared to corresponding samples of non-heat treated wood. Little is known about the reasons for this phenomenon.
        Recent studies illuminated several terms, which had been considered vital to the fungal growth within fresh pine sapwood after the heat treatment. It was shown that different parameters in the material changes significant during the heat treatment: the content of elutable lipid components as well as the content of free sugars increased whereas the ph-value of the wood decreased. However, a migration of free sugars into the outer layer as well as a stimulation of thermophilic fungi, or a change of the moisture distribution in the cross-section could not be proved. Further investigations led to environmentally compliant agents to inhibit temporarily the fungal germination on wood packaging surfaces. Alkaline agents reduce the content of fats, probably by saponification. Nevertheless, drying (either naturally or technically) is indispensable to avoid fungal hazard in the long run. A combination of temporary alkaline treatment immediately after sawing followed by air drying seems to be the most effective and economically method to protect ISPM No 15 treated wood packaging material against discoloring fungi.
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Key words: blue stain, free fatty acids, free sugars, mould, ph-value, phytosanitary treatment, wood packaging material.

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