## 4 Discussion  
In the European Pharmacopoeia, the oak bark is described as the bark of young branches and the lateral shoots of _Q. robur_, _Q. petraea_ and/or _Q. pubescens_. On the other hand, older bark is considered to be forest waste [2]. Considering the enormous quantities of forest waste, particularly from older bark [7], it is essential to successfully recover the active biomolecules from these sources. The combination of environmental consciousness, financial motivations and international legislation provide incentives for the recovery of the organic waste phytocompounds and the subsequent secondary utilization of those compounds. The present study describes the histo-anatomical structure of the older oak bark (_Quercus robur_ bark) together with the phytochemical composition and biological activity of the extracts. Studies on the biological activity of some of the extracts obtained from oak bark do not present clear information about the histo-anatomical structure of the plant matrix that was studied. It is clear that the chemical composition of the extracts were influenced by the type of tissue correlated with the age of the tree and the other external factors acting on the plant [21]. The histo-anatomical structure was described in order to define the plant tissue that was subjected for extraction. Thus, the histo-anatomical structure of the oak bark consists of a sequence of periderm and secondary phloem in accordance with the descriptions previously observed in the specialized literature [22]. Figure 3: Graphical representation of the dependence between the logC (of the concentration expressed as ug/mL) and the inhibition percentage against the \(\alpha\)-glucosidase of the _Q. robur_ older bark extracts, using the activity of acarbose as the positive control. The polyphenols and tannins content were in line with the anatomical observations. The bark of \(Q\). _robur_ was rich in polyphenols that could be solubilized by different polarity solvents. In this study, a significantly higher TPC was observed for the hydroethanolic bark extracts that were obtained using MAE. On the other hand, the higher values of tannins were quantified in the aqueous extracts. The TPC in the oak bark extracts indicates that the older oak bark is a valuable source of biomolecules. Similar reports were previously given for other oak bark extracts, even though the extraction procedures differed, or the plant matrix was not histo-anatomically characterized. For example, for ethanol-water extracts (50:50, \(v/v\), bark from a 17-year-old \(Q\). _robur_ tree, UAE extraction) the TPC was 610.63 mg GAE/g for the dried bark extract [23], which was higher compared to the older oak bark extracts that were characterized in this work (50:50, \(v/v\), bark from a 90 to100-year-old \(Q\). _robur_ tree, UAE/MAE extraction). Another study [24] reported a much lower TPC (54.3 mg GAE/g for the dried bark extract) compared to our results. In this case, the hydroethanolic extract was obtained from the bark of a 148-year-old tree using the Soxhlet extraction method. It can be considered that the extraction type and the age of the oak tree influenced the concentration of the biomolecules in the bark extracts., The differences between the TPC values could also be linked with a gradual decomposition of the phenolic compounds over time [24]. The presence of the phenolic compounds could be correlated with the biological potential (antioxidant, antimicrobial, antidiabetic etc.) of the bark extracts. Due to the differences in the methods and calculations, the comparison between the results and the literature data should be done with caution. However, our results are in agreement with those from the previously published literature [6; 8]. As can be observed, the older oak bark extracts exerted a high antioxidant activity, an expected activity given the high polyphenic content. According to research from the literature, ellagic acid - a key bioactive component - could be partially responsible for the antioxidant properties of the oak bark extracts [6].