## 3 Results and Discussion
### Growth Stimulatory Activity  
The Greek endemic plant extracts of _A. citrodota_ were tested for their potential growth stimulatory effects on two lactobacilli strains. The results indicated significant (\(p<0.05\)) growth stimulatory of _L. rhamns_ GG and _L. rhamns_ OXLAL-1 strains at 0.5 mg (dry matter)/mL of the aqueous extract (Figure 4a). Furthermore, _A. citrodota_ ethanolic extract stimulated the growth of both lactobacilli only at 0.25 mg (dry matter)/mL (\(p<0.05\)), while no stimulatory activity was recorded at the other concentrations tested (\(p>0.05\), Figure 4b). In addition, the prebiotic index ranged above 1 for both _L. rhamns_ strains incubated with _A. citrodota_ aqueous extract at all concentrations with a significantly increased value at 0.5 (dry matter)/mL (\(p<0.05\), Figure 5a). For the ethanolic extract, prebiotic index values ranged at lower levels, but a significantly increased prebiotic index was recorded at 0.25 mg (dry matter)/mL (\(p<0.05\), Figure 5b). A prebiotic index exceeding the value of 1 suggests a positive stimulatory effect on probiotic growth, while values below 1 indicate low effectiveness. The results of the osmotic stress using NaCl at various concentrations demonstrated that _A. citrodota_ aqueous extract significantly promoted the cell growth of _L. rhamns_ GG at 0.5 mg (dry matter)/mL in NaCl-supplemented MRS (1-4% \(w/v\), \(p<0.05\)), while no significant growth was observed at 6-10% \(w/v\) NaCl (\(p>0.05\)) (Figure 6a,b). On the contrary, _A. citrodota_ aqueous extract reported no substantial contribution to _L. rhamns_ OXLAL-1 growth in the presence of NaCl (1-10% \(w/v\), \(p>0.05\)). Bile salt tolerance assay showed an increased survival rate of _L. rhamns_ OXLAL-1 incubated with _A. citrodota_ aqueous extract [0.5 mg (dry matter)/mL, \(p<0.05\)] after 4 h (Figure 7b). Interestingly, no effect was observed for _L. rhamns_ GG incubated with the _A. citrodota_ aqueous extract (\(p>0.05\)) (Figure 7a). The results of the stimulatory activity of the aqueous _A. citrodota_ extract [0.25-0.5 mg (dry matter)/mL] on the lactobacilli strains regarding their performance under thermal stress at 52 \({}^{\circ}\)C revealed that the plant extract had a positive effect on _L. rhamns_ GG cell growth (\(p>0.05\)) even after 30 min of exposure. On the other hand, no growth stimulatory effect was reported for _L. rhamns_ OXLAL-1 at 52 \({}^{\circ}\)C, since the final cell counts ranged at similar levels between the examined cases and the control (\(p>0.05\)) (Figure 8a,b). The above mentioned result might suggest that _L. rhamns_ OXLAL-1 possibly possesses thermally resistant properties. Figure 3: Chemical structures of the main identified phytochemicals. When subjected to alcohol stress, cell growth of \(L\). _thamosus_ OLYAL-1 was positively affected by \(A\). _citrodot_ aqueous extract at 0.5 and (dry matter)/mL (\(p\) < 0.05) compared to the controls, even at the highest alcohol concentration, 12% \(v/v\) (Figure 9b). A positive effect was also documented on \(L\). _thamosus_ GG (\(p\) > 0.05), only at 4% and 6% alcohol, where the addition of 0.5 (dry matter)/mL \(A\). _citrodot_ aqueous extract significantly promoted cell growth (\(p\) < 0.05, Figure 9a). No stimulatory activity was reported for \(L\). _thamosus_ GG in other alcohol concentrations. Figure 4: Effect of (**a**) aqueous and (**b**)_ethanolic \(A\). _citrodot_ extracts [mg (dry matter)/mL] as growth stimulators of _Lactiaseibacillus rhamnosus_ GG and _Lactiaseibacillus rhamnosus_ OLYAL-1. Significant difference (\(p\) < 0.05) compared to the control (MRS broth) is indicated with *. Similar results regarding the stimulatory effect of plant extracts were observed in benoidin-based anthocyanins extracted from purple sweet potato (_Ipomoea battats_ ([PERSON].) [43], as well as in culinary spice extracts on various beneficial microbes, including _L. rhamnosus_ strains [44].