## 4 Conclusions  
This study evaluated the antifungal activity of three commercial natural plant extracts against three industrial _S. cerevisiae_ strains: a wine, a beer, and a baker's strain. _S. cerevisiae_ is widely used as model eukaryotic microorganism but comprises numerous strains with significant genetic and phenotypic differences that are not well investigated [15,16]. In this study, _S. cerevisiae_ strains were used as yeast models that are sustainable and well adapted to environmental pressures to assess the potential application of the natural plant extracts against yeast food spoilage. The antifungal activity of the natural plant extracts was assessed using three different methods, and it can be concluded that the degree of antimicrobial activity detected varied according to the applied method. In the agar disc diffusion method, only the rosemary extract appeared to be fungistatic against all the tested yeasts compared to the other two extracts. The spot assay method revealed mild antifungal activity against the wine and beer yeast by all of the natural extracts; the carrier oils showed similar antifungal activity, thus the antimicrobial activity of the extracts was \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **Hypericum** & **Rosemary** & **Liquid Mastic** \\  & & **Extract** & **Extract** & **Extract** \\ \hline
1 & Pyrogallic acid & 5.4 \(\pm\) 0.01 & 5.4 \(\pm\) 0.01 & 5.4 \(\pm\) 0.01 \\ \hline
2 & Na-salicylate & 17.5 \(\pm\) 0.01 & n.d * & 17.5\(\pm\) 0.01 \\ \hline
3 & Catechol & 32.0 \(\pm\) 0.01 & 32.0 \(\pm\) 0.01 & 32.0 \(\pm\) 0.01 \\ \hline
4 & Tartaric acid & n.d & 31.1 \(\pm\) 0.02 & 31.1 \(\pm\) 0.02 \\ \hline
5 &
\begin{tabular}{c} 3,5-dimethoxy-4- \\ hydroxy tannic acid \\ \end{tabular} & 29.7 \(\pm\) 0.02 & 29.7 \(\pm\) 0.02 & 29.8 \(\pm\) 0.02 \\ \hline
6 & Quercetin & 22.2 \(\pm\) 0.02 & 22.2\(\pm\) 0.01 & 22.2 \(\pm\) 0.02 \\ \hline
7 & Rutin & 33.2 \(\pm\) 0.02 & n.d & 33.2 \(\pm\) 0.02 \\ \hline
8 & Curcumin & 62.5 \(\pm\) 0.01 & 62.5 \(\pm\) 0.01 & 62.5 \(\pm\) 0.01 \\ \hline
9 & Tannic acid & n.d & 26.5 \(\pm\) 0.01 & n.d \\ \hline
10 & Catechin & 12.4 \(\pm\) 0.01 & 12.4 \(\pm\) 0.01 & 12.4 \(\pm\) 0.01 \\ \hline
11 & Silymarin & n.d & n.d & 47.4 \(\pm\) 0.06 \\ \hline
12 & Deosmin & 37.5 \(\pm\) 0.03 & 37.5 \(\pm\) 0.03 & 37.5 \(\pm\) 0.03 \\ \hline
13 & Kampferol & 49.9 \(\pm\) 0.03 & 49.9 \(\pm\) 0.03 & 49.9 \(\pm\) 0.03 \\ \hline
14 & Coumaric acid & 24.8 \(\pm\) 0.01 & 24.8 \(\pm\) 0.01 & 24.8 \(\pm\) 0.01 \\ \hline
15 & Ascorbic acid & n.d & n.d & 2.8 \(\pm\) 0.01 \\ \hline
16 & Cinnamic acid & n.d & n.d & 2.9 \(\pm\) 0.01 \\ \hline
17 & Gallic acid & 4.4 \(\pm\) 0.001 & 4.4 \(\pm\) 0.001 & 4.4 \(\pm\) 0.001 \\ \hline \hline \end{tabular}  
* n.d: non detected.  
\end{table} 
Table 1: Detection and Retention time (min) of phenolic compounds in hypericum (_H. perforatum_), liquid mastic (_P. lentiiscus var. Chia_), and rosemary (_R. officinalis_) extracts. not demonstrated. However, a more comprehensive analysis of the fungistatic activity was observed in the growth curve analysis, which revealed statistically significant slower growth rates of all yeasts in the presence of the natural plant extracts. Therefore, it was shown that the natural plant extracts delayed the growth of the _S. cerevisiae_ strains studied. Also, the three yeast strains in this study exhibited differences in their susceptibility to pharmaceutical antifungals, and two of them were found to have acquired resistance to itraconazole (beer yeast and baker's yeast). A common characteristic of the samples was the carrier oils, which most likely hindered the inhibitory effect of the natural extracts due to low diffusivity in the agar disc method [43]. Yet, it is important to underline that mild antifungal activity of the oil carriers was only detected in the spot assay method.