## 3 Results and Discussion
### The Effect of Essential oils on the Viability of Bifidobacterium in In Vitro Conditions
This suggests that the action of a particular essential oil on a given bacterial species depends on the composition of the essential oil, the interaction between its components, and the concentration of the essential oil used. The effect of an essential oil is also influenced by the conditions under which its activity is tested and by the bacterial species and strains used for the analysis, as each strain is different and exhibits different sensitivities. [PERSON] et al. [55] emphasized that it is difficult to compare the results obtained by various authors regarding the antibacterial action of different essential oils. This is due to the fact that the composition of oils obtained from the same plants may differ due to changes that occur in plants under the influence of climatic and environmental factors. Essential oils with the same name can often be produced from different plant species. Moreover, the type of method used to measure the sensitivity of microorganisms to the essential oil is of great importance. Depending on the methods used, the tested microorganisms may experience different growth conditions and may be exposed to the essential oil to different degrees. The solubility of the emulsifier and essential oil, as well as its components in a given environment, may also vary. To the best of our knowledge, studies such as those performed in our work, i.e., using a well-diffusion method and exploring the influence of various concentrations of clove bud, lemon peel, and juniper berry essential oils on the survival of _Bifidobacterium_ bacteria have not been conducted earlier (the well-diffusion method is applied in experiments concerning plant extracts rather than essential oils). The Effect of Essential Oil Concentrations on the Viability of B. animals Subsp. lactis Bb-12 in Cream during Fermentation and after 21 Days of Storage  
The strain _B. animals_ subsp. _lactis_ Bb-12 that was selected for the experiments was identified as the most sensitive to the tested essential oils. If there was no influence of the tested essential oils and their concentrations on the viability of the most sensitive strain (_B. animals_ subsp. _Lactis_ Bb-12) in the cream, we assumed, with a high degree of certainty, that the other tested bifidobacterial strains would also not show a sensitivity to the tested essential oils added to the fermented cream. The number of _B. animals_ subsp. _lactis_ Bb-12 cells present in our samples of fresh cream (before fermentation) ranged from 8.1 to 8.3 log(CFU/mL), regardless of the type of oil used and the concentration of the oil tested (Table 3). After fermentation, a change in the population of bifidobacterial cells was recorded and the statistical analyses showed that the final population of _B. animals_ subsp. _Lactis_ Bb-12 cells in the obtained sour cream was not influenced by the type of essential oils, or the concentration used. The sour cream samples were stored for 21 days under refrigeration conditions to investigate the deferred or cumulative influence of the tested essential oils on the viability of _B. animalis_ subsp. _lactis_ Bb-12. It was noted that refrigerated storage caused a statistically significant reduction in the population of _B. animalis_ subsp. _lactis_ in the sour cream samples; however, the dynamics of changes did not depend on the type of essential oils, or the concentration of the oils used. In all stored sour cream samples, the number of live _B. animalis_ subsp. _lactis_ Bb-12 cells ranged from 7.5 to 7.8 log(CFU/mL). Our previous study examined the effect of commercial essential oils on the growth of selected LAB [56; 57], as well as the effect of plant extracts on the populations of LAB, which showed that LAB cultures tolerated the extracts present in milk well, at an amount of up to 3.0% [58]. The effects of coriander essential oils (concentrations from 1% to 100%) on the growth inhibition of the studied _Lactobacillus_ bacteria (7 _L. acidophilus_ strains, 7 _L. casei_ strains, 3 _L. delbrueckii_ strains, 3 _L. plantarum_ strains, 3 _L. rhamnus_ strains, _L.