Norway spruce (Picea abies (L.) Karst.) bark contains marked amounts of polyphenolic compounds. Condensed tannins (CTs) and stilbenes show commercial potential as antioxidants, antimicrobials, preservatives in food and cosmetic applications, technochemical products, and pharmaceuticals. Storing of bark before the conversion process leads to substantial losses of extractives compounds. In the present study, the potential of thermal drying for maintaining extractives content was assessed based on an experiment in which bark samples were dried in convection kilns at 40, 50, 60, and 70 °C temperatures. The development of CTs and stilbene contents and CT degradation were followed for 28–34 h. CTs were analysed from bark samples with thiolysis. Quantities of stilbene glycosides and stilbene aglycones in water-acetone extracts were analysed applying gas chromatography with flame-ionization detection (GC-FID). Multilevel regression analysis was used to analyse the statistical differences in moisture content and extractives composition between the drying schemes.

The initial CT content of 35–36 mg g⁻¹ in dry bark material declined to 25–31 mg g^-1 in 28–34 h. The average degree of polymerisation (DP) decreased slightly, and the relative proportion of prodelphinidins in CTs increased significantly in the 60 and 70 °C schemes. The proportion of A-type linkages slightly increased with the increase in drying temperature. The initial mean stilbene contents varied from 19 mg g⁻¹ to 22 mg g⁻¹ in dry bark mass. Isorhapontin was the major stilbene constituent, with a proportion of 45–49 % of the total stilbenes. Stilbene losses of up to 60 % were detected during the drying processes. In 10 h, for example, 36–43 % of total stilbenes were lost. Degradation activities by enzymes released from the bark and oxidative reactions after crushing at the debarking phase were concluded to be the primary mode of degradation. The results indicate that bark CT content can be preserved at a moderate temperature not exceeding 50 °C, but the degradation of CTs may affect their suitability for various applications. Sufficient stilbene content for industrial processes is unlikely to be maintainable through thermal drying. The permanence of the post-drying extractives content should be assessed based on a practical-scale storage experiment using bark dried to varying moisture contents.

挪威云杉 ( Picea abies(L.) Karst.) 树皮含有显着数量的多酚化合物。缩合单宁 (CT) 和芪作为抗氧化剂、抗菌剂、食品和化妆品应用中的防腐剂、技术化学产品和药物显示出商业潜力。在转化过程之前储存树皮会导致提取物化合物的大量损失。在本研究中，基于在 40、50、60 和 70 °C 温度下在对流窑中干燥树皮样品的实验，评估了热干燥在保持提取物含量方面的潜力。CTs和二苯乙烯含量的发展以及CT降解被跟踪28-34小时。用硫解法从树皮样品中分析 CT。应用气相色谱与火焰离子化检测器 (GC-FID) 分析水-丙酮提取物中二苯乙烯苷和二苯乙烯苷元的含量。多级回归分析用于分析干燥方案之间水分含量和提取物成分的统计差异。

干燥树皮材料中 35-36 mg g ^-1的初始 CT 含量在 28-34 小时内下降到 25-31 mg g ^-1。在 60 和 70 °C 方案中，平均聚合度 (DP) 略有下降，CTs 中原飞燕草素的相对比例显着增加。随着干燥温度的升高，A型连杆的比例略有增加。初始平均二苯乙烯含量从 19 mg g ^-1到 22 mg g ^{-1 不等}在干燥的树皮块中。Isorhapontin 是二苯乙烯的主要成分，占二苯乙烯总量的 45-49%。在干燥过程中检测到高达 60% 的芪损失。例如，在 10 小时内，总二苯乙烯损失了 36-43%。树皮释放的酶的降解活性和剥皮阶段破碎后的氧化反应被认为是主要的降解方式。结果表明，树皮 CT 含量可以在不超过 50 °C 的适中温度下保存，但 CT 的降解可能会影响其对各种应用的适用性。通过热干燥不太可能保持足够的二苯乙烯含量用于工业过程。