## 2 Materials and Methods
### Antimicrobial Activity Assay
The solvents are quite economical, but the standards compounds are expensive. The identification of standards, the wavelengths and the retention time of each compound are shown in Table 1. The response intensity and retention time of the chromatographic peaks from the three analyses almost overlap, which shows limited variations due to instrument errors. The chromatographic method was optimized for the quantitative analysis of 14 compounds in LAB strains within a run period of 60 min. Based on the results, the three standards (phenyllactic acid (28 min); hydrocinnamic acid (38 min); 34-Dihydroxyhydrocinnamic acid (45.3 min)) were identified at 255 nm (Figures 1 and 2). Compared to phenyllactic acid and 34-dihydroxyhydrocinnamic acid, all the tested standards showed higher absorbance at 255 nm. The main metabolites that were detected in the tested LAB strains are presented in Table 2. _Lactiplantiobacillus plantarum_ was a unique strain that produced all six detected metabolites (Figures 3-5). DL-p-Hydroyphenyllactic acid (OH-PLA) was identified in the metabolites of three of the tested LAB. The highest concentration (217.8 ppm) was found in _Lactiplantiobacillus plantarum_ and the lowest (103.4 ppm) in _Levilactobacillus brevis_ (Table 2). A similar quantity of vanillic acid range (2.6-3.4 ppm) was identified in _Levilactobacillus brevis_ and _Lactiplantiobacillus plantarum_, respectively. Ferulic acid was isolated in different concentrations in _Lacticaseobacillus rhamnus_ and _Lactiplantiobacillus plantarum_ ranged from 4.9 to 6.4 (Table 2). It was observed that the metabolites produced by the tested LAB species in the broth medium remained the same over a period of 30 days while the concentrations increased in the broth (Table 3). Thus, metabolites could be identified from the first day of incubation of the microorganism. None of these compounds was detected in the blank MRS broth. The analysis was implemented during a 30 day period. The concentration of each metabolite was determined at a 5 day interval, as shown in Table 3. In the present study, the concentration of metabolites increased until the 10 th day. Afterward, the metabolites' concentrations followed a stable pattern [27]. [PERSON] [28] et al., (2015), investigated the antifungal activity of _L. reuteri_ R29 and the production of antifungal carboxylic acids in wheat sourdough. The results of the study showed that _L. brevis_ R2D produced ferulic acid (22 mg/mL), salicylic acid (1 mg/mL), vanillic acid (8 mg/mL) and 3-phenylacetic acid (8 mg/mL). [PERSON] et al. (2014), studied the case of _Lactiplantiobacillus plantarum_ for the potential production of antimicrobial compounds. The results showed that the metabolic compounds identified in _L. plantarum_ were 4.8 mg/mL of OH-PLA, 1.03 mg/mL of 4-hydroxybenzoic acid, 0.04 mg/mL of caffeic acid, 43 mg/mL of phenyllactic acid, 0.46 mg/mL of coumaric acid, 0.13 mg/mL of 3-(4-hydroxy-3-methoxy) propanoic acid, 0.29 mg/mL of benzoic acid and 1.2 mg/mL of ferulic acid. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name of Standard** & _Levilactobacillus brevis_ & _Lactiplantiobacillus_ & _Lacticaseibacillus_ \\  & **(ppm)** & _plantarum_ **(ppm)** & _rhamouss_ **(ppm)** \\ \hline (A) 4-Hydroxybenzoic acid & - & - & - \\ (B) DL-p-Hydroyphenyllactic acid & 103.4 & 217.8 & 147.6 \\ (C) Phenyllactic acid & - & - & - \\ (D) 3-(4-Hydroxyphenyl) propionic acid & - & - & - \\ (E) Hydrocinamic acid & - & - & - \\ (F) Methylcinamic acid & - & - & - \\ (G) Salicylic acid & - & 1.8 & - \\ (H) 1,2-Dihydroxybenzene & - & - & - \\ (I) 3,4-Dihydrocinamic acid & - & - & - \\ (J) Vanillic acid & 2.6 & 3.4 & - \\ (K) 3,4-Dihydroxyhydrocinamic acid & - & - & - \\ (L) Ferulic acid & - & 6.4 & 4.9 \\ (M) Benzoic acid & - & 4.6 & - \\ (O) 4-Hydrocinamic acid & - & 1.4 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Concentration (in ppm) of the 14 tested compounds determined in _Levilactobacillus brevis_, _Lactiplantiobacillus plantarum_ and _Lacticaseibacillus_ chultures.