## 3 Results & Discussion
### Elucidation of the Phytochemical Composition of LRE  
The phytochemical composition of extracts is strongly linked to their antimicrobial potential. Previous works focused on glabridin, a prenylated flavonoid that could be extracted from licorice roots and has shown antimicrobial activity against _Listeria_ bacteria and other foodborne pathogens and spoilage microorganisms [38; 39]. Glabridin can reduce _L. monocytogenes_ motility and hemolytic activity, but was not found to have antimicrobial activity [38; 39]. Furthermore, prenylated (iso)flavonoids and chalcones from roots exert potent inhibitory effects on many bacteria and yeasts [40]. Thus, the phytochemical composition of LRE was elucidated using an advanced LC-DAD- qTOF-MS set-up to accurately identify its active phytoconstituents. Peak identification was based on retention times, UV-Vis spectra, mass spectra, and mass information from the literature. Chromatographic \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{_Listeria_ **Strains and Serotypes**} & \multicolumn{2}{c}{**MIC (\(\upmu\)g mL\({}^{-1}\))**} & \multicolumn{2}{c}{**MBC (\(\upmu\)g mL\({}^{-1}\))**} \\ \cline{2-5}  & **Ethanol** & **Water** & **Ethanol** & **Water** \\ \hline _L. monocytogenes_ ATCC 23,074 (serotype 4b) & 31.3 & 125 & 62.5 & 500 \\ _L. monocytogenes_ EGD (serotype 1/2a) & 31.3 & 125 & 250 & 500 \\ _L. monocytogenes_ Scott A (serotype 4b) & 62.5 & 250 & 125 & 500 \\ _L. monocytogenes_ NCTC 7973 (serotype 1/2a) & 31.3 & 125 & 62.5 & 250 \\ _L. monocytogenes_ NCTC 4885 (serotype 4b) & 62.5 & 125 & 125 & 250 \\ _L. monocytogenes_ NCTC 4994 (serotype 4b) & 62.5 & 125 & 125 & 250 \\ _L. monocytogenes_ NCTC 1792 (serotype 4b) & 62.5 & 125 & 125 & 500 \\ _L. ivanovii_ NCTC 11846 & 62.5 & 250 & 125 & 500 \\ _L. grayi_ NCTC 10815 & 62.5 & 250 & 250 & 500 \\ _L. seeligeri_ NCTC 11856 & 31.3 & 250 & 250 & 500 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of licorice root extract dissolved in ethanol and water against _Listeria_ strains. MIC and MBC values are expressed as (\(\upmu\)g mL\({}^{-1}\)). analysis revealed an extract rich in phytochemicals with great structural diversity. Table 2 summarizes the identified compounds; the presence of all phytochemicals has been previously described in plants belonging to the _Glycyrrhiza_ genus and their derivatives [41; 42; 43; 44; 45]. The majority of LRE phytochemicals belong to the flavonoid class, as previous studies reported [46; 47]. More specifically, a great variety of flavanones, as well as flavones and chalcones, were found in the extract. In addition, LRE contains triterpenols typical of licorice extracts, while the presence of coumarins and phenolic acid was also confirmed. The presence of all these compounds has been reported in licorice extracts in previously published works. Table 2 also clearly demonstrates that the liquiritin-apioside isomers are the major constituents of LRE, as their total content reaches 133.1 mg g\({}^{-1}\) of extract. The results show a concentrated content of these isomers in LRE compared to licorice root extracts of different geographical origins [48]. [(2Z)-3-(4-tert-Butyl-2-hydroxyethyl)-3-hydroxypropyl-2-enoyl]benzoic acid was also found at high concentrations in LRE (32.9 \(\pm\) 0.8 mg g\({}^{-1}\) extract). Licorice glycoside isomers are also prominent constituents in LRE. These are glycosylated flavonoids, which are typical compounds in _Glycyrrhiza glabra_ roots. In addition, LRE contains significant amounts of flavanone-type compounds: namely, kanzonol C, kanzonol W, and kanzonol Y. Unfortunately, the triterenoid content of LRE could not be determined. According to previous works, the glycyrrhizin contents in _G. glabra_ roots vary from 11 to 80 mg g\({}^{-1}\), depending on genetic and environmental factors, while glycyrrhetic and oxo glycyrrhetic acids, hydrolytic products of glycyrrhizin, are present in licorice root extracts at very low levels [49; 50].