Yield of stilbene glucosides from the bark of young and old Norway spruce stems

Bioactive stilbene glucosides are the major constituents of the acetone extracts of the phloem and bark of Norway spruce (Picea abies (L.) Karst.) trees. We studied their variation patterns across phloem and bark within the stems of Norway spruce. The total yields of stilbene glucosides (astringin, isorhapontin, and piceid) from trees were estimated. Bark samples were collected from young (18 years-old) and older trees (37 years-old), representing age and size typical for energy wood harvesting and the first commercial thinning, respectively. Different bark layers of younger trees had 10%–63% lower average amount of stilbene glucosides than the bark layers of older trees. The inner bark had the highest mass fraction of stilbene glucosides (2.7%–4.8% of dry weight (d.w.)) and the outermost bark showed the lowest amount (0.4%–1.2% d.w.). Axially along the stem, the highest amount of stilbene glucosides was found at the stem base in the young trees (average over bark zones 2.1% d.w.) and at the breast height and the base of the living crown in the older trees (average over bark zones 3.6% d.w.). Astringin and isorhapontin yielded the highest amounts, while the share of piceid was the smallest. The total yield of stilbene glucosides was dependent on the bark biomass, and positively correlated with total wood and bark volume. The basal stem was the most valuable stilbene source in both younger and older trees. The bark of Norway spruce from the first commercial thinnings, especially of butt and middle logs, can provide feasible source for high-value extracts.