## 3 Results and Discussion
### The Effect of Essential oils on the Viability of Bifidobacterium in In Vitro Conditions
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Bifidobacteria** & **The Concentration of** & \multicolumn{2}{c}{**Lemon Peel**} & \multicolumn{2}{c}{**Clove Bud**} & \multicolumn{2}{c}{**Juniper Berry**} \\
**Strain** & **the Essential Oil [\%]** & **Mean** & \(\pm\)**SD (mm)** & **Mean** & \(\pm\)**SD (mm)** & **Mean** & \(\pm\)**SD (mm)** \\ \hline \multirow{5}{*}{HN 019} & 100 & 0.0 & \(\pm\)0.0 \({}^{\text{a}}\) & 5.6  
[PERSON] et al. [43] referred to the research of other authors on the influence of essential oils on the growth of microorganisms. Based on the studies that analyzed the antibacterial effects of essential oils and their active substances, these authors argued that the bioactivity of essential oils was generally associated with phenolic compounds. Phenolic compounds dissolve in a lipid diaphragm layer and change their membrane liquidity, as well as causing the leakage of intracellular components and the scattering of transmembrane gradient H\({}^{+}\). Thus, the inhibitory effect of the citrus extract on the growth of bacteria can be linked with the substances it contains. Citrus extract was found to be a natural source of antioxidants, flavonoids (rutin, naringin, quercetin, and naringenin), and other phenolic compounds, such as limonene, linalool, and citral. Therefore, it has been proposed that the bioactivity of the citrus extract may be the effect of the synergistic activity of these components. The results reported by [PERSON] et al. [42] on of the antibacterial effects of lemon essential oils differed from that obtained in our work. [PERSON] et al. [42] showed that lemon oil exhibited a stronger antibacterial effect than that observed in the present work. This could be due to the differences in the methods used for analyses, as well as the bacterial species tested. In their study on the influence of lemon essential oils on anaerobic bacteria that affect the teeth and oral cavity, which were grown from materials collected from patients, [PERSON] et al. [44] found that the essential oil decreased the number of the analyzed bacteria. These results confirmed that Gram-positive bacteria were more sensitive to the antibacterial effects of lemon essential oils compared to Gram-negative bacteria. Among the Gram-positive bacteria group analyzed by [PERSON] et al. [44], there were two _B. breve_ strains, and these bacteria were inhibited by the citric essential oil. The minimum inhibitory concentration (MIC) values determined for both strains were the same, and amounted to 15 mg/mL. In summary, lemon oil inhibited the growth of certain types of bacteria, with a stronger effect on Gram-positive bacteria. However, its activity was weaker compared to the essential oils obtained from other plants such as cloves, cinnamon, and bergamot. In our study, the clove bud essential oil was particularly distinguished from other tested essential oils due to the size of the bacterial growth zone (Table 2). This essential oil had a statistically significantly higher inhibitory effect on the growth of all tested _Bifidobacterium_ strains. Compared to the other two essential oils, clove oil appeared to have significantly higher amounts of carnation oil. [PERSON] et al. [43] showed that eugenol did not inhibit the growth of _Lactobacillus_ bacteria (_L. plantarum_ and _L. brevis_). [PERSON] et al. [45] compared the antimicrobial activity of three spices, cardamom, cinnamon, and clove, and essential oils obtained from them, using 13 strains of Gram-positive and Gram-negative bacteria, seven fungal strains, and two yeast strains. They showed that the clove essential oil had the strongest effect. Clove oil also showed stronger antimicrobial activity than phenol. Furthermore, this essential oil was one of the three tested essential oils that showed antibacterial effects on pathogenic _S. aureus_ bacteria. These results confirm the strong antibacterial effect of clove bud essential oils observed in our work.