Increase in the content of extractives in Scots Pine (Pinus sylvestris L.) during ISPM-15 heat-treatment and correlation with fungal discoloration
2009
Lambertz, Gerda | Welling, Johannes
According to International Standard of Phytosanitary Measures (ISPM No 15), heat treatment is the most important method to avoid the spreading of harmful quarantine organisms like insects and nematodes when using wood-packaging material. The standard defines heat treatment at 56 degrees 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 particulary 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 origin of this occurrence. - Recent studies illuminated different parameters, which had been considered vital to the fungal growth within fresh pine sapwood after the heat treatment. 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. But it was shown that the content of some extractives increased during the heat treatment. By further investigations environmentally compliant agents could be identified, which inhibit temporarily the fungal germination on wood packaging surfaces. Alkaline agents reduce the content of lipophilic fraction, 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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