Hot water extraction of Norway spruce (Picea abies [Karst.]) bark: analyses of the influence of bark aging and process parameters on the extract composition.

The hot water (HW) extraction of Norway spruce
(Picea abies [Karst.]) delivers condensed tannins and considerable
amounts of other compounds. Yield and composition
of the HW extracts were investigated as a function of
natural weathering for up to 15 months. Total phenol monomers
and oligomers were detected by Folin-Ciocaltau
assay after fractionation by solid phase extraction (SPE).
Procyanidins (PC) were determined by HPLC-UV after acid
thiolysis and carbohydrates by HPLC combined with acid
hydrolysis. Topochemistry of the bark before and after
extraction was investigated by UV-
microspectrometry
(UMSP) and non-extractable PC analyzed by direct thiolysis
on the bark. The influence of the parameters on
the yield and composition of the extracts were evaluated,
such as the extraction temperature, time and the addition
of sodium sulfate and urea. Prolonged weathering
resulted in a considerable decrease of the total extraction
yield, partly because of leaching of phenolic monomers,
mono- and oligosaccharides. The yield of phenolic
oligomers also decreased at a moderate rate, while the
yield of polysaccharides (pectins) was almost stable. Nonextractable
and non-leachable compounds deposited in
the cell lumens represent the majority of the phenolic
extractives in spruce bark. Sequential extractions performed
at increasing temperature proved to be a suitable
method for the recovery of tannin-rich extracts.