Volatile chemical profiling and distinction of Citrus essential oils by GC analyses with correlation matrix; evaluation of its in vitro radical scavenging and microbicidal efficacy

Abstract

Leaf volatile oil compositions of five Citrus species viz., Citrus aurantifolia, Citrus limon, Citrus maxima, Citrus medica and Citrus medica * Citrus limon were examined in this study by Gas Chromatography-Flame Ionisation Detector (GC-FID) and Gas Chromatography-Mass Spectrometry (GC–MS) analysis and percentage volatile compositions were compared. Thirty-eight compounds were identified that account for 90 to 99 % of essential oil composition from Citrus species, respectively. GC–MS profiling of essential oils revealed that Citrus leaf oils were predominantly characterized by limonene (15.76±0.01% to 29.36±0.46%) as one of the major constituents. Monoterpenoids (77.38±0.19% to 98.05±0.05%) are the prominent class of constituents present in the volatile oils of four Citrus plants under study whereas in one species (C. maxima), sesquiterpene hydrocarbons (38.97±0.21%) were the dominant category. The data from GC analyses were subjected to correlation study to analyse the correlation between the volatile constituents among the selected Citrus species. These essential oils were initially evaluated for their antioxidant capacity and the leaf oils exhibited promising radical scavenging property with an average IC50 value of 29.15±0.01 μg/mL. This study was further designed to evaluate antimicrobial efficacy of five Citrus leaf essential oils against various pathogenic bacterial and fungal strains. Four examined essential oils gave a comparative antibacterial activity with a minimum inhibitory concentration (MIC) value against tested bacterial strains ranging from 3.62±0.02mg/mLto60.0±0.32mg/mL.Citrus leaf oils were found to be more sensitive to Escherichia coli with MIC values ranged between 3.62±0.03 to 10.15±0.02 mg/mL. These essential oils also exhibited strong inhibitory potential against tested fungal strains, Aspergillus niger and Candida albicans, with MIC ranging from 3.22±0.02 to 28.17±0.04 mg/mL. Out of the five essential oils screened in this study, four of them have shown significant antimicrobial and antioxidant activities which can be attributed to synergistic potential of major monoterpenoid constituents present in these oils viz., geranial, neral, citronellal, nerol, geraniol, geranyl formate rather than the sesquiterpene dominated essential oil. Based on the findings obtained and conclusions derived, it is evident that the selected Citrus leaf essential oils are promising natural agents to fight free radical damage and antibiotic-resistant microbes.