Potential and utilization of water extracts from spruce bark

Abstract

The aim of this thesis was to investigate potential ways to utilize water extracts from spruce bark. Spruce bark has been found to contain three main stilbene glucosides (astringin, isorhapontin, polydatin), which have potential in the treatment of skin aging and cosmetics applications. Since stilbene glucosides are water soluble, they are dissolved into the debarking process waters of the pulp and paper industry. These waters are not fully utilized at the moment, and being considered as a waste stream, which adds to the costs of the mill by increasing COD levels of the waste water. This waste stream could potentially be transformed to a source of stilbene glucosides, to provide additional revenue to the mill.

In the experimental part, temperature effect on hot water extraction yields of industrial spruce bark was studied. Mechanical pressing of heated spruce bark was performed with a laboratory scale mechanical press to study the effect on the COD levels. Finally, bark press waters obtained from the mill were characterized, with partial purification of stilbene glucosides by ultrafiltration with 2 and 5 kDa filters. The yields were calculated by gravimetric and spectroscopic analysis. Two dimensional (2D) solution-state 1H–13C correlation NMR spectroscopy provided the structural verification of the stilbene glucosides and other compounds present in the samples.

Extraction yield of industrial spruce bark was increasing 1.4 times every 20 ◦C, on average, reaching yield of 5.0% at 80 ◦C. The mechanical pressing was able to press out 26±5% of the total mass of the sample. COD level was 75,100 mg/L for 80 ◦C sample. This was two times higher compared to bark press sample of taken from a paper mill, which had COD level of 37,500 mg/L. Ultrafiltration could remove 90% of polyphenols and permeated 14% of the stilbenes of the feed. With 2D-HSQC NMR, all three major stilbene glucosides were identified from the filtrate and the feed.