Birch in the Northern hemisphere is a very widespread tree genus, which is extensively used in the furniture, pulp and plywood manufacture where, as a by-product, it accumulates birch bark (BB) in the process, which does not find industrial application, and is often burned as fuel. BB comprises about 12.5 wt.% of the tree mass. Outer BB actually consists of a mixture of pentacyclic triterpenes (35–40 wt.%) and biopolyester suberin (45 wt.%). Betulin, betulinic acid and lupeol, representatives of triterpenes, are biologically active substances, whose efficiency can be enhanced by synthetic modification. Betulin in the outer BB powder form is used in folk-medicine as an anti-inflammatory agent. Betulinic acid selectively kills human melanoma cells while leaving healthy cells intact and is found to delay the progression of the HIV 1 infection, which eventually leads to AIDS, by preventing the formation of syncytia. Freshly isolated BB, left over at a plywood factory, was chosen as a representative of industrial waste. Milled dry BB samples were soaked by mixing from time to time in deionized water for 24 h. Outer BB floated on the top of water and this component were collected and dried at room temperature and in a drying cabinet at 50oC up to a moisture content of 1–10 wt.%. Milled outer BB (≤ 2 mm) was pelletized on a laboratory flat die type pelletizer with holes of diameter 6 mm. The temperature equilibrium on the die was approximately 100oC. Extraction of triterpenes was carried out in Soxhlet apparatuses by the selected solvents (ethanol – water mixtures in the range of 75 to 95 vol%, acetone, cyclohexane and heptane) for 1-11 h. The components were identified with gas chromatography/mass spectroscopy by comparison of the spectra with those of the standards. The properties and composition of BB were evaluated to gain information for selecting a technology, convenient for obtaining triterpenes. In the case of the flotation method, the pure outer BB yield was around 40 wt.%. Pelletization increased the outer BB bulk density up to 470 kg/m3. The yield of cyclohexane and heptane extractives was considerably lower than that in the case of acetone and ethanol. However, the more selective solubility eliminated the amount of undesirable substances, e.g., polyphenols, tannins, etc. from the total extract.
Keywords: Outer birch bark, Flotation, Pelletization, Extraction, Triterpenes
Authors
Pazhe A.
Department of Technological Research, Latvian State Institute of Wood Chemistry, Riga, Latvia
Zandersons J.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Rizhikovs J.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Dobele G.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Spince B.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Jurkjane V.
Latvian State Institute of Wood Chemistry, Riga, Latvia
Tardenaka A.
Latvian State Institute of Wood Chemistry, Riga, Latvia
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