## 3 Results  
Selected medicinal plant fruits, air- and freeze-dried (Table 1), were analyzed using UHPLC-ESI-MS/MS to determine the presence of individual polyphenols: EA and Q. Additionally, the total phenolic content (TPC) and total flavonoid content (TFC) were measured using spectrophotometric methods. Although rosehips also belong to one of the most frequently used wild fruits, they were excluded from this study, as they have already been extensively investigated for EA content [25]. LC-MS/MS using electrospray ionization (ESI) is susceptible to sample matrix components, which may lead to either suppression or enhancement of the signal of the analyte (so-called matrix effect). Through the determination of TPC and TFC, we can obtain general information about the compositional characteristics and diversity of the studied material, as well as predict potential matrix effects. Matrix-matched calibration can be used for compensation of the matrix effect and helps to obtain quantitatively accurate results [26]. Thus, we decided to apply this strategy in our study. Regarding the unique composition of the studied fruits, for quantitative analysis, matrix-matched calibration curves were built for each plant material. The parameters of the calibration curves, LODs, and LOQs are summarized in Table 2.  
Examples of chromatographic results for EA and Q determined in wild fruit extracts are presented in Figure 1.  
The calculated contents of free EA and Q were expressed in \(\mu\)g per gram of dry material, and the obtained results are presented in Table 3. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Type of Fruit Matrix** & **Analyte** & **LR [\(\mu\)g/g]** & **EC** & **R\({}^{2}\)** & **LOD [\(\mu\)g/g]** & **LOQ [\(\mu\)g/g]** \\ \hline \multirow{2}{*}{Barberry} & EA & 1.51–151.10 & \(y=24.9x-57.3\) & 0.997 & 0.45 & 1.36 \\  & Q & 1.51–151.10 & \(y=579.9x-1274.3\) & 0.992 & 0.45 & 1.51 \\ \hline \multirow{2}{*}{Blackthorn} & EA & 1.51–151.10 & \(y=35.4x-83.6\) & 0.989 & 0.45 & 1.51 \\  & Q & 7.55–151.10 & \(y=880.6x-8440.7\) & 0.986 & 2.42 & 7.10 \\ \hline \multirow{2}{*}{Chokeberry} & EA & 1.51–151.10 & \(y=46.7x+42.2\) & 0.997 & 0.45 & 1.51 \\  & Q & 1.51–151.10 & \(y=690.5x-892.9\) & 0.992 & 0.45 & 1.36 \\ \hline \multirow{2}{*}{Elderberry} & EA & 0.76–151.10 & \(y=34.3x-16.4\) & 0.999 & 0.30 & 0.76 \\  & Q & 1.51–151.10 & \(y=655.3x+6699.2\) & 0.998 & 0.45 & 1.36 \\ \hline \multirow{2}{*}{Hawthorn} & EA & 0.76–151.10 & \(y=59.5x+25.0\) & 0.998 & 0.24 & 0.76 \\  & Q & 0.76–151.10 & \(y=723.2x-701.9\) & 0.994 & 0.21 & 0.66 \\ \hline \multirow{2}{*}{Lingenberry} & EA & 1.51–151.10 & \(y=39.1x+29.5\) & 0.998 & 0.45 & 1.36 \\  & Q & 1.51–151.10 & \(y=398.0x+768.7\) & 0.996 & 0.45 & 1.51 \\ \hline \multirow{2}{*}{Rowanberry} & EA & 1.51–151.10 & \(y=32.3x-0.5\) & 0.990 & 0.45 & 1.36 \\  & Q & 1.51–151.10 & \(y=451.1x+9411.4\) & 0.993 & 0.45 & 1.21 \\ \hline \multirow{2}{*}{Sea-buckthorn} & EA & 0.76–151.10 & \(y=52.6x+104.1\) & 0.998 & 0.15 & 0.60 \\  & Q & 0.76–151.10 & \(y=520.3x+3036.8\) & 0.994 & 0.30 & 0.76 \\ \hline \end{tabular}  
* LR—linear range of the calibration curve; EC—equation of the calibration curve; \(y\)—concentration of the analyte [\(\mu\)g/g] \(x\)—peak area of the analyte; R\({}^{2}\)—the coefficient of determination.  
\end{table} 
Table 2: Parameters of calibration curves, LODs, and LOQs for EA and Q determined for the studied fruit matrices. The determined EA contents varied among samples, ranging from below the LOD (in some chokeberry and hawthorn fruit samples) to over 3 \(\mathrm{\SIUnitSymbolMicro g}\)/g dw. Blackthorn, barberry, and sea-buckthorn exhibited significantly (\(p<0.05\)) higher EA content compared to other studied fruits (Figure 2A). The highest EA contents were found in sea-buckthorn (from 2.53 to 4.80 \(\mathrm{\SIUnitSymbolMicro g}\)/g of dry material, mean 3.84 \(\mathrm{\SIUnitSymbolMicro g}\)/g, n = 3).