Fate of Antioxidative Compounds within Bark during Storage: A Case of Norway Spruce Logs

Abstract

Softwood bark is an important by-product of forest industry. Currently, bark is under-utilized and mainly directed for energy production, although it can be extracted with hot water to obtain compounds for value-added use. In Norway spruce (Picea abies [L.] Karst.) bark, condensed tannins and stilbene glycosides are among the compounds that comprise majority of the antioxidative extractives. For developing feasible production chain for softwood bark extractives, knowledge on raw material quality is critical. This study examined the fate of spruce bark tannins and stilbenes during storage treatment with two seasonal replications (i.e., during winter and summer). In the experiment, mature logs were harvested and stored outside. During six-month-storage periods, samples were periodically collected for chemical analysis from both inner and outer bark layers. Additionally, bark extractives were analyzed for antioxidative activities by FRAP, ORAC, and H2O2 scavenging assays. According to the results, stilbenes rapidly degraded during storage, whereas tannins were more stable: only 5–7% of the original stilbene amount and ca. 30–50% of the original amount of condensed tannins were found after 24-week-storage. Summer conditions led to the faster modification of bark chemistry than winter conditions. Changes in antioxidative activity were less pronounced than those of analyzed chemical compounds, indicating that the derivatives of the compounds contribute to the antioxidative activity. The results of the assays showed that, on average, ca. 27% of the original antioxidative capacity remained 24 weeks after the onset of the storage treatment, while a large variation (2–95% of the original capacity remaining) was found between assays, seasons, and bark layers. Inner bark preserved its activities longer than outer bark, and intact bark attached to timber is expected to maintain its activities longer than a debarked one. Thus, to ensure prolonged quality, no debarking before storage is suggested: outer bark protects the inner bark, and debarking enhances the degradation.

The Bark of Picea abies L., a Waste from Sawmill, as a Source of Valuable Compounds: Phytochemical Investigations and Isolation of a Novel Pimarane and a Stilbene Derivative

“…A novel finding of this work is the isolation of two new compounds, and this result indicates that further studies are needed to deepen the knowledge regarding Norway spruce bark composition. Furthermore, it suggests that storage of the bark can also contribute to chemical modification of some of the constituents, as previously indicated [ 40 ], since the highly oxygenated new terpenoids may be formed during bark storage. This paper reports the isolation of 15 main constituents, namely 21 α -metoxy-serrat-14-en-3-one ( 1 ), 21 α -hydroxy-serrat-14-en-3-one ( 2 ), pinoresinol ( 3 ), dehydroabietic acid ( 4 ), 15-hydroxy dehydroabietic acid ( 5 ), 7-oxo dehydroabietic acid ( 6 ), pimaric acid ( 7 ), 9 β -pimara-7,15-dien-19-ol ( 8 ), and 13-epimanoyl oxide ( 9 ) from the lipophilic extracts, and taxifolin-3′-O-glucopyranoside ( 11 ), trans-astringin ( 12 ), and piceasides G and E ( 14,15 ) from the methanolic fraction.…”

“…The present study aimed to fully characterize the phytochemical components of Norway spruce bark waste, and results indicate its possible use as source of phytoconstituents. Other groups have previously considered this bark as valuable source of phytoconstituents [ 38 , 39 , 40 ], but our work and results give new approaches in the exploitation of this waste. The approach based on sequential extractions allowed the characterization of several classes of compounds and led to a more complete knowledge of the chemical composition of Norway spruce bark extract.…”

Characterisation, Recovery and Activity of Hydrophobic Compounds in Norway Spruce Log Soaking Pit Water: Could they be Used in Wood Preservative Formulations?

“…The crude SLSW contained phenolic acids, lignans, flavonoids, stilbenes and procyanidins eluted from the woods soaked on them. These constituents identified in crude SLSW are commonly present in Norway spruce bark [43].…”

“…Overall, it is important to highlight that despite the lowor negative-antifungal and wood-preserving properties of the crude SLSW and EHC solution, this cheap and abundant liquor contains several constituents of interest to the wood-preserving industry; once purified, it also has high antioxidant activity. It must be highlighted that the concentration of these constituents in Norway spruce bark might vary depending on the felling season [55], storage duration [43,56], and the water temperature used to soak the liquid, as different temperatures will cause variations in the extraction yield of extracts from Norway spruce [57].…”

Behaviour of Extractives in Norway Spruce (Picea abies) Bark during Pile Storage

“…However, it seems practically inevitable that some forms of raw material storage must be used, and finding a solution that does not compromise the quality of the raw material ought to be considered to be of great importance. Storing bark in an intact form on saw logs has already been discussed in previous studies [10,11]. It seems evident that such a form of storage has many advantages, as compared to pile storage, in preserving extractives in bark.…”