Phenolic Content and in Vitro Antioxidant, Anti-Inflammatory and antimicrobial Evaluation of Algerian Ruta graveolens L.

Plants constitute a valuable source of natural antioxidants such as polyphenols and are responsible for exhibiting many biologically significant functions. Ruta species including Ruta chalepensis L. and Ruta graveolens L. are widespread species in Algeria and are used as medicinal plants to treat various diseases; however, so far, most of the conducted studies focused on analyzing alkaloids and essential oils mostly on R. chalepensis. The aim of the present research is to investigate the phenolic profile of the aerial parts of Ruta graveolens L. from Algeria and assess its in vitro antioxidant, anti-inflammatory and antimicrobial properties. The total polyphenols and flavonoids were assessed using colorimetric methods, and the individual polyphenols were identified and quantified using HPLC-DAD-ESI-MS. The antioxidant activity was evaluated with DPPH and ß-carotene tests, and the anti-inflammatory activity with inhibition of bovine serum albumin denaturation and HRBC membrane stabilization methods. The results showed that Ruta graveolens extract is rich in phenolic compounds with a total phenol and flavonoid contents of 41.63±0.394 mg GAE/gE and 13.97±0.33 mg EQ/gE, respectively. Nine phenolic compounds were determined, including three phenolic acids and six flavonoids. Rutin was the major phenolic compound in Ruta graveolens (464.95 µg/g), followed by syringic acid (179.74 µg/g), and naringenin (109.78 µg/g). R. graveolens phenolic extract also showed good antioxidant activity with values of 0.77 mM TE/g DW and 0.37 mM ß-CE/g DW with DPPH and ß-carotene tests, respectively. For the anti-inflammatory activity, the highest tested concentration (200 µg/mL) gave 50.61 % of inhibition of the denaturation of albumin and 44.12 % of membrane stabilization. With regards to antimicrobial results, Staphylococcus aureus was the most sensitive bacteria with an inhibition zone of 14.37 mm and MIC value of 0.625 mg/mL, followed by Listeria monocytogenes (11.75 mm and MIC=1.25 mg/mL), and Escherichia coli (10.25 mm and MIC=1.25 mg/mL).

Antimicrobial Activity of Selected Polyphenols and Capsaicinoids Identified in Pepper (Capsicum annuum L.) and Their Possible Mode of Interaction.

Antimicrobial activity of pepper polyphenols and capsaicinoids (Coumarin, caffeic acid, narangin, kaempferol, rutin, quercetin, capsaicin, and dihydrocapsaicin) against 13 pathogen bacteria and three beneficial strains was studied using the disk diffusion and microdilution methods. In general, phenolic compounds had the most important activity with the highest inhibition zones obtained with caffeic acid (3.5-20.5 mm), quercetin (4.75-3.5 mm), and kaempferol (7-14 mm). In the determination of the minimal inhibitory concentrations, the effects of both quercetin and kaempferol were more important than caffeic acid. The clinical strains Staphylococcus aureus (319, 14, 8, 32, and 550) were more sensitive to quercetin (0.00195-0.0078 mg L-1) whereas kaempferol was more active against the strains S. aureus (ATCC 6538, 26), S. typhimurium ATCC 13311, and Pseudomonas aeruginosa ATCC 27853 (0.0156-0.125 mg L-1). The interaction between these three polyphenols was studied against S. aureus ATCC 6538 and P. aeruginosa ATCC 27853. Different modes of interaction were observed (synergism, additive, and indifferent), but no antagonism was obtained. The best combination was quercetin and caffeic acid for S. aureus with fractional inhibitory concentration index (FICI) of 0.37, and kaempferol with quercetin for P. aeruginosa (FICI = 0.31).