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        BIOACTIVE STILBENES FROM NORWAY SPRUCE (PICEA ABIES) ROOT BARK.

Harri Latva-Mäenpää1,2*, Daniel Mulat2, Tapio Laakso1, Tytti Sarjala3, Kristiina Wähälä2 and Pekka Saranpää1

(1) Finnish Forest Research Institute (Metla), P.O. Box 18, 01370 Vantaa, Finland
(2) Laboratory of Organic Chemistry, Department of Chemistry, P.O. Box 55, FI-00014 University of Helsinki, Finland
(3) Finnish Forest Research Institute (Metla), 39700 Parkano, Finland
*harri.latva-maenpaa@metla.fi


In the world today, there is a need and also a desire for new natural and more environmentally friendly
products. Roots and stumps of conifer trees contain considerable amounts of wood biomass, usually left in
the forest after felling the timber or used for combustion and energy production. Conifer trees and
especially their bark contain bioactive polyphenolic compounds which could be utilized after extraction and
isolation. With already existing techniques the thick roots and stumps of Norway spruce might offer a base
for a sustainable value chain for producing novel biochemicals. They could be used for different
applications for example in food, healthcare or wood working industry.
       Norway spruce (Picea abies [L.] Karst.) bark contains stilbene glycosides. We have studied hydrophilic
extractives from Norway spruce stumps and different parts of thick roots. According to our results,
especially root bark next to the stem might be a rich source of stilbenes such as trans-astringin and
trans-isorhapontin. These stilbene glucosides could be hydrolyzed to their aglycones, which posses even
more bioactive properties. Stilbenes have been shown to be potent anti-inflammatory, anti-cancer,
antioxidant, anti-aging and chemoprotective agents. In addition, they have been found to be active against
termites.
       We have further developed a laboratory scale extraction and isolation of the stilbene glycosides and
aglycones from Norway spruce root bark. The freeze dried root bark powder was extracted by ASE
(Accelerated Solvent Extractor) with ethanol-water as a solvent. The extract rich in stilbene glucosides was
further hydrolyzed enzymatically after evaporation of the solvent. The enzymatic hydrolysis was performed
in buffer solution with β-D-glucosidase. The solution was incubated at 39 °C for three days. After hydrolysis,
polyphenolic compounds were purified directly from the hydrolysate mixture with the polymeric resin
sorbent. The hydrolysed and purified extract containing mainly stilbene aglycones trans-isorhapontigenin
and trans-piceatannol (including also minor compounds such as trans-resveratrol and residual stilbene
glycosides) was injected to preparative HPLC to collect the pure compounds. Also stilbene glycosides were
purified and isolated from the crude extract. The compounds were analysed and identified with GC- and
HPLC-MS and NMR.
       Stability of Norway spruce bark extract and its stilbene compounds has been under discussion. Solid
extract and its methanol solution as well as isolated stilbenes in methanol were monitored for their stability
when exposed to fluorescent light and stored in freezer (dark and at -20 °C). This study revealed that solid
trans-stilbenes were stable when exposed to light, but in solutions they were isomerized to mainly cis
isomers and in rare case oxidized to o-benzoquinones for those with a cathecol moiety. Our results also
showed that stilbenes in methanol were stable for at least 2 weeks when stored in glass vials and protected
from light. Verification of possible oxidation products of stilbenes is still in progress.
       In the future our aim is to optimise the extraction, analysis and isolation methods. Also bioactive
properties of isolated compounds and their possible chemical modification will be studied for different
applications.

				
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posted:12/7/2011
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