Characterization of essential oil composition of Juglans regia bark, comparison of secondary metabolites and biological activities of its extracts

Aromatic and medicinal plants form a reservoir of active molecules; among them, Juglans regia is a plant of the Juglandaceae family, and it is used thanks to its medicinal properties. The present study was conducted to investigate the secondary metabolite content and biological activities of the infusion, methanolic extracts, and essential oil of the bark essential oil (EO) of Juglans regia harvested from North Tunisia, as well as its chemical composition. Essential oil, infusion, and methanolic extracts were prepared. Identification of essential oil composition was determined using GC-MS. Phenolic content, antioxidant, and antimicrobial activities were evaluated with the colorimetric method. The obtained data indicate that J. regia is very abundant in bioactive compounds. The infusion extract of J. regia bark has been found to contain elevated amounts of phenolic compounds. The infusion extract showed stronger antioxidants and radical scavenging action than methanol. The studied methanolic extract displayed antimicrobial activity against all ten tested microbial strains but with variable degrees according to the microbial strain. The infusion extract, instead, was inactive. The use of gas chromatography coupled with mass spectrometry (GC-MS) revealed the existence of 34 components in the bark (EO). The main compounds were: carvacrol (13.82%), isoeugenol (13.71%), β-caryophyllene (7.81%), 1,8-cineole (8.60%), and bornyl acetate (7.13%). Our results suggest that Juglans regia is a natural source of potent antioxidants and antimicrobials and may be useful as preventive agents in some diseases.