Spruce bark extracts may be lost during storage

FM Eelis Halmemies In his doctoral dissertation in chemistry at the University of Jyväskylä, he studied various industrial side streams from spruce: their chemical composition, how the composition changes during storage, and how different extractive fractions can be separated using different solvents.

In Finland, industrial processing of spruce produces millions of cubic meters of spruce bark as a side stream each year, which mainly ends up being burned in energy production.

"However, spruce bark contains valuable compounds, such as those with health benefits, that could be utilized in products with much higher processing value," says Halmemies.

In order for biorefineries to utilize industrial side streams in a usable form, further processing requires researched information on the chemical changes in the raw material during storage.

Cancer cure from the bottom of a stump?

Interesting compounds obtained from spruce include stilbenes, tannins and lignans.

"For example, lignans, which are known to have anti-cancer properties, are found at the bottoms of spruce stumps and the inner bases of branches," says Halmemies.

Stilbenes and tannins are found in spruce bark. Stilbenes are natural antioxidants that protect wood. Tannins are polyphenolic compounds that have a wide range of applications, for example in wastewater treatment.

The research developed both gas and liquid chromatographic methods that were able to separate and identify different types of compounds.

Storage matters

Storage experiments revealed that when spruce bark was stored in a pile as usual, the stilbene content decreased rapidly.

“Microbiological processes begin to break down the material quickly, and within just a few weeks, stilbene concentrations decrease significantly. Stilbenes were preserved significantly better in the logs.”

If the extractives are to be preserved, the side streams should be stored in as large pieces as possible and protected from moisture.

“Many beneficial substances are leached out if the material is exposed to water. In addition, the material should be protected from sunlight and stored in a cool place to minimize the decomposition process – water-soluble extractives are often bound to sugars, which is why insects, fungi and microbes use them as food.”

The carbohydrate and lignin contents of the bark were also examined. A surprising result was that the amount of lignin seemed to increase, especially during pile storage.

"It would be interesting to investigate in more detail what causes it," says Halmemies.

Link to Eelis Halmemiehen dissertationn