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A major problem within forest industry is unwanted browsing on seedlings from mammalian herbivores. The aim of this study was to evaluate the effects of birch bark extracts as repellents towards fallow deer. Birch bark was extracted in a conventional way with ethanol as solvent at ambient temperature and with a new method, liquid CO 2 extraction. An analysis of the ethanol-extracted birch bark showed that it contained large amounts of terpenoids, of which the most abundant was betulin. In seven different treatment trials, we used 15 individually handled fallow deer. To investigate the binary taste preferences, birch bark extract was added to food and presented in two bowls in typical two-choice tests. We found that the amount of a food type consumed during a trial and the number of shifts between food bowls were dependent on the amount of the birch extract the food contained. Concentrations of above 1 % by dry weight of birch extract acted as a repellent. In addition, such concentrations produced shorter feeding bouts by a greater willingness to change bowls. Therefore, our conclusion is that birch bark extract acts as a repellent towards fallow deer and is therefore likely to act as a repellent against other deer species. In addition, we show that birch bark extract produced by the new and more environmentally sustainable method employing liquid CO 2 mixed with ethanol has the same repellent effect as the traditional ethanol extraction. [ABSTRACT FROM AUTHOR]

Pressurized hot (subcritical) water and ethanol were used to extract betulin and antioxidants from birch bark. Betulin was found to be the major compound (around 26% (w/w)), which was able to be extracted with ethanol (120 °C, 50 bar, 15 minutes) but not with water at any of the temperatures tested (40–180 °C, 50 bar). The obtained extraction result for betulin is supported by theoretical solvation parameter calculations. Furthermore, high antioxidant activity of the extract was obtained using both ethanol and water as solvent. The antioxidant activity, as determined by a DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, was found to be highest for the water extract of finely ground bark and it markedly increased with elevated extraction temperatures (90–180 °C). To elucidate if this was due to increased extraction efficiency or chemical reactions, a set of experiments was performed in which the samples were pre-treated with water at different temperatures before extraction. Results from liquid chromatography showed some differences in molecular composition between samples pre-treated at ambient and 180 °C, respectively. However, more detailed studies have to be performed to distinguish between hot-water extraction and reaction kinetics. [ABSTRACT FROM AUTHOR]