**4. Conclusions**

The results of this study indicate that MAE is an efficient extraction method of phenolic compounds from beech bark. The optimum conditions which gave the highest TPC (76.57 mg GAE/g dry plant material) were reached when the microwave power was 300 W, the extraction time was 4 min, and the solvent was a mixture of ethanol–water (50:50). The practical value of TPC after a control experiment was 76.49 mg GAE/g dry plant material.

The extracts obtained in optimum conditions were characterized by HPLC-MS/MS. The identified compounds in all tested BBEs were: vanillic acid, epicatechin, catechin, protocatechuic acid, chlorogenic acid, ferulic acid, and isoquercitrin. Quercetin and gallic acid were identified only in beech bark extract obtained with 100%water.

The beech bark extracts exhibited free-radical-scavenging activity in all assays, and were active against *S. aureus, P. aeruginosa, S. typhimurium,* and *E. coli*. All tested *Candida* species were sensitive to beech bark aqueous extract. Additionally, all extracts were active on α-glucosidase. The beech bark extracts assayed may be considered to have low or no antimutagen effects.

This study documented that *Fagus sylvatica* L. bark possesses antioxidant activity and has α-glucosidase inhibitory effects, by several *in vitro* experiments. Ethanol and water extracts can be considered as promising sources of natural antioxidants, antimicrobian agents, and α-glucosidase inhibitors. The isolation of bioactive constituents and investigations on several biomedical properties of *F. sylvatica* bark should be conducted in future experiments.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-3921/8/9/417/s1, Table S1: ANOVA—complete summary of the regression and residual analysis.

**Author Contributions:** Conceptualization, C.T. and A.M.; methodology, C.T., A.M., O.C., A.G., S.C., A.N.; software, A.G.; resources, C.T., D.C.V., O.C.; data curation, C.T., A.-M.G., S.C., D.C.V., O.C., A.-M.G.; writing-original draft preparation, C.T.; visualization, A.M., D.-L.M.; supervision, D.-L.M., O.C.; project administration, C.T.; funding acquisition, C.T.

**Funding:** This work was supported by a grant of Ministry of Research and Innovation, CNCS-UEFISCDI, project number PN-III-P1-1.1-PD-2016-0892, within PNCDI III.

**Conflicts of Interest:** The authors declare no conflict of interest.
