# Phenolic Compounds in Trees and Shrubs of Central Europe
## 3 Results
### Phenolic Compounds
#### 3.1.4 Stilbenes  
Stilbenes are metabolites of the phenylpropanol pathway, activated under biotic and abiotic stress. They are compounds with a 1,2-diphenylethylene skeleton. Only some unrelated plant species are capable of synthesising and accumulating stilbenes. The enzyme facilitating this synthesis is stilbene synthase (STS). In plants, stilbenes serve several functions, among which the most significant is related to strong antimicrobial properties; thus, they are classified as phytoalexins [142]. Other known functions also include their repellent action against herbivores, as well as their allebotathic and antioxidant properties. Stilbenes are produced in small amounts; however, biosynthesis is activated primarily post infection, while it is also triggered by wounding, UV radiation, ozone and aluminium ions. Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is one of the most extensively described stilbenes [142; 143; 144]. Resveratrol is found in the form of two isomeric forms: cis and trans (Figure 1). Transresveratrol is a phenol stilbene found in many plants, e.g., the grape family (Vitaceae), and is particularly common in grape vines (_Vitis vinifera_). The other form of resveratrol, i.e., cis, is formed as a result of the  
Figure 4: Dimeric 4\(\rightarrow\)8 B type proanthocyanidin chemical structure [140; 141]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Tree and Shrub Species** & **Proanthocyanidins** & **Literature** \\ \hline \multirow{4}{*}{Scots pine _Pinus sylvestris_ L. _Pinus_ _densiflora_ L. needles} & \multirow{4}{*}{Proanthocyanidins (OPC)} & \multirow{4}{*}{[124; 125; 126; 127; 128]} \\  & & procyanidins, prodelphinidins and \\  & & propelargonidins catechin \\  & & derivatives, both dimers \\  & & and trimers. \\ \hline \multirow{2}{*}{_Quercus petraea_ L. and _Q. _robur_} & Proanthocyanidins & [129; 130; 131; 132] \\ \cline{2-3}  & & \\ \cline{2-3}  & & \\ \hline \multirow{2}{*}{Bird cherry _Prunus padus_} & Cyanidin-3-trutinoside and & \multirow{2}{*}{[135]} \\  & & cyaniding-3-glucose & \\ \hline \multirow{2}{*}{_Salix purpurea_ L.} & Cyanidin-3-glucose, myrtillin & \multirow{2}{*}{[136]} \\  & & (delphinidin-3-glucose) & \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Proanthocyanidins (condensed tannins) found in trees and shrubs. isomerisation of trans-resveratrol and after the decomposition of resveratrol polymer molecules during the fermentation of grape skins, due to the action of UV radiation, and at high pH [144]. Resveratrol was first isolated in 1940 from the roots of _Veratum gradiforum_[145]. Its highest concentration was recorded in the roots of Japanese knotweed (_Polygonum cuspidatum_). In folk medicine, this plant was successfully used to treat pyoderma, mycoses and venereal diseases [146]. Moreover, resveratrol has been applied in cancer prevention and treatment thanks to its ability to effectively inhibit each stage of neoplasia, i.e., the initiation, promotion and progression of the disease [147,148]. Stilbenes are secondary metabolites that are relatively rarely found in nature (Table 10). To date, they have been reported in almost 70 unrelated plant species belonging to approx. 30 genera and 12 families. The greatest stilbene contents are detected in plants from the pine family (_Pinaceae_), the grape family (_Vitaceae_), the beech family (_Fagaceae_), the mulberry family (_Moraceae_) and the grass family (_Poacae_) [141]. The presented literature sources indicate that phenolic substances of plant origin, particularly those obtained from trees and shrubs growing in a temperate climate zone, exhibit a beneficial effect on human health. Thanks to the presence of bioactive compounds in those plants, they have found applications as detoxicants, vitamin supplements, as well as preparations boosting immunity and adjunctive medication in the treatment of various diseases. There is a considerable body of data indicating that a diet rich in bioactive compounds plays a significant role in the prevention of cardiovascular diseases and cancer.