*3.3. Identification and Quantification of Individual Polyphenols*

The optimized extracts obtained from the beech bark (water—BBE1, 50% (v/v) ethanolic—BBE2 and 80% (v/v) ethanolic—BBE3) were investigated in terms of their phytochemical profile. For the individual polyphenols identification and quantification, the previously described LC-MS/MS analytical methods were employed. The results of this analysis are summarized in Table 4 [15].


**Table 4.** Quantitative (μg/g dry plant material) evaluation of the recovery of main bioactive compounds in samples of BBE.

Notes: NF—not found, below limit of detection; BBE1—extracts obtained with water 100%, BBE2—extracts obtained with ethanol–water 50:50, BBE3—extracts obtained with ethanol–water 80:20. Data are shown as mean ± standard deviation (SD).

From the 18 phenolic compounds analyzed by the LC-MS/MS method, chlorogenic acid, ferulic acid and isoquercitrin, were identified in all tested BBEs. Quercetin was identified only in beech bark extract obtained with 100%water (BBE1). From the phenolic compounds identified by this method, only ferulic acid found in BBE1, was quantified (43.7 ± 5.03 μg/g dry plant material). The polyphenols (epicatechin, catechin, syringic acid, protocatechuic acid, and vanillic acid) analyzed by the other LC-MS method were identified and quantified in all tested BBEs (Table 4). Gallic acid was identified only in BBE1.

In previous studies some of the phenolic compounds obtained from beech bark were identified, including catechin, epicatechin, quercetin, taxifolin, procyanidins, syringic acid, coumaric acid [11,12].
