Influence of sugar and starch content of palm wood on fungal development and prevention of fungal colonization by acid treatment
Schmidt, Olaf | Magel, Elisabeth | Frühwald, Arno | Glukhykh, Lidia | Erdt, Katharina | Kaschuro, Sergej
Freshly harvested palm trunks and timber with their high moisture content (MC) are susceptible to fungi due to the high content of easily consumable sugars and starch as long as MC of the tissue is above fiber saturation point (FSP). To test the influence of sugars and starch on fungal development, small wood samples from oil palm (Elaeis guineensis) were watered and their contents of the non-structural carbohydrates were measured. Glucose was the most abundant substance in the extract, followed by starch, fructose, and sucrose. Watering for 3 and 10 days with daily water exchange reduced the content of sugars and starch considerably. Untreated and watered samples were then subjected to spore suspensions of the moulds Aspergillus niger, Penicillium commune, to a natural infection by air-born spores and to the blue-stain-fungi Alternaria alternata and Aureobasidium pullulans. The former colonized the surface of the untreated samples within a few days, while the latter caused considerable mass loss. With increasing watering both fungal activities were reduced as the nutrients for the fungi were removed. The woods of E. guineensis and Phoenix dactylifera (date palm) with MC above FSP were treated with acetic and propionic acid and subsequently infected by moulds, staining and decay fungi. Short dipping in solutions of 2% acetic acid and 2% propionic acid, respectively, protected all samples for 3 months against the mould fungi. Staining fungi and wood-decay fungi were slightly inhibited by a treatment with 5% acid concentration. Treatment with these acids offers a protection technique for the practice. Their sodium salts were ineffective due to their high pH-value.
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