Polyphenolic profile and biological properties of Arbutus unedo root extracts

Introduction: Arbutus unedo (Ericaceae) is a medicinal plant used traditionally to treat several diseases including oxidative stress related diseases and infectious diseases. However, the antimicrobial and antioxidant actions of A. unedo and its bioactive compounds have not been well studied. Therefore, the aim of this study was to evaluate the antioxidant and antibacterial activities of Arbutus unedo roots extracts and to investigate the action of their major compounds. Methods: The roots were exhaustively extracted by high-pressure static extraction using the Zippertex® technology, with different solvents (water, methanol, ethyl acetate, and dichloromethane). The antioxidant activity of A. unedo root extracts were examined using DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging and FRAP (Ferric Reducing Antioxidant Power) procedures. The root extracts were tested against four reference health-damaging bacteria (Escherichia coli, Salmonella Typhimurium, Staphylococcus aureus, and Pseudomonas aeruginosa) by the agar well diffusion and broth dilution assays. Results: The results of this study showed that ethyl acetate extract of A. unedo roots have the highest contents of phenols and flavonoids with a value of 590.31±17.62 mg GAE/g extract and 47.42 ± 1.80 mg RE/g extract, respectively. Moreover, the same extract exhibited the most potent antioxidant activity with the half maximal inhibitory concentration (IC50) and half maximal effective concentration (EC50) doses of 0.02±0.01 and 0.15±0.01 mg/mL, respectively. This result is similar to those showed by ascorbic acid and quercetin. According to the broth microdilution method, the methanolic plant extract revealed the highest antibacterial activity against S. aureus with a minimal inhibitory concentration (MIC) value of 12.5 mg/mL. This extract was most effective against S. aureus (inhibitory zone=15.4±0.2 mm), E. coli (inhibitory zone=12.2±0.2 mm), and Salmonella (inhibitory zone=10.2±0.1 mm) as revealed in the disc diffusion assay. The antibacterial activity of the extracts confirmed by the predicted results of molecular docking studies, and same amino acids in dihydrofolate reductase (DHFR) enzyme interact with both catechin and reference adenosine diphosphate (ADP) in similar modes. Conclusion: The present data suggest that A. unedo the root extracts have potential antioxidant activity and antibacterial effect against selected bacterial strains, which may have a potential therapeutic use against oxidative stress related pathologies and infectious diseases. However, other investigations on A. unedo extracts and their bioactive compounds are needed to consider their application as nutraceuticals and functional foods.