Chemical Composition and Biological Activities of Essential Oils from Selected Medicinal Plants of Soon Valley

Abstract

Plants are recognized as the richest source of biologically active components called as plant secondary metabolites such as steroids, phytolipids, alkaloids, phenolics and antimicrobial agents. Many plant species are popular due to containing complex mixtures of volatile compounds, mainly composed of terpenoids, with specific essence and odour. The complex mixture of these components obtained from plants is regarded as essential oils. Recently, the essential oils are gaining valuable importance as a good source of antioxidants in nature and harmless bioactives with promising biological and pharmacological applications. During the recent few years, a lot of research is happening to appraise the composition and biological potential of plant EOs (essential oils). The present research work was mainly planned to appraise the variations in physicochemical parameters, composition as well as biological attributes of EOs isolated from four selected medicinal plants such as Euclayptus (Eucalyptus camaldulensis), Basil (Ocimum basilicum), Coriander (Coriandrum sativum) and Mentha (Mentha piperita) using two different techniques including hydro-distillation (HD) and super critical fluid extraction (SCFE). The selected plants were harvested from Soon Valley of Punjab, Pakistan which has specific agroclimatic conditions compared with the adjacent areas. The yields of essential oils from the areal parts of the selected medicinal plants by SCFE and HD revealed significant (P <0.05) variations between the extraction techniques. Overall, the yields of hydro-distilled plants essential oils were higher than the SCF extracted essential oils; hydro-distilled Eucalyptus essential oil gave the highest yield among others. Nevertheless, among the selected plants, the least essential oil yield was obtained from Eucalyptus using SCFE. The results regarding physicochemical parameters showed that the tested SCF extracted essential oils were somewhat denser and had higher refractive index than the essential oils obtained by HD. According to GC/GC-MS compositional analysis, the major chemical component identified in Eucalyptus essential oil, isolated using both the SCFE and HD techniques, was found to be eucalyptol; other important components detected were α-pinene, spathulenol, globulol etc. Linalool was the principal chemical component in Basil EO isolated by either of the techniques while estragole, piperitone oxide, and α- xix bergamotene were some of the other key chemical compounds detected in this oil. Mentha essential oil, produced by either of the techniques, was mainly composed of menthol and menthone. Meanwhile, SCF extracted and hydro-distilled Coriander essential oil contained linalool as a major component followed by α-pinene, phytol, camphor etc. Statistically notable variations were observed in quantitative chemical composition in the selected plant essential oils in relation to SCFE & HD that can be linked to the operational conditions and efficacy of the technique employed. The biological activities of the tested essential oils were evaluated by studying their antioxidant (TPC, TFC, DPPH free radical scavenging capacity and reducing power), antimicrobial (using bacteria and fungus), biofilm inhibition and hemolytic activities. The results showed that the maximum TPC, TFC and DPPH radical scavenging capacity were exhibited by SCF extracted essential oil of Coriander while the essential oil of Eucalyptus obtained by SCFE had superior reducing power among others. Overall, the plants essential oils isolated by SCFE had superior antioxidant capacity as compared to the essential oils obtained by HD. While from the data of antimicrobial activity it was noted that among the selected plants essential oils, isolated by either technique, Coriander essential oil acted as a better antibacterial and antifungal agent against the tested microorganisms. The essential oil of Eucalyptus obtained by SCFE exhibited superior biofilm inhibition potential while the hydro-distilled EO from Coriander gave the minimum hemolytic activity. Based upon the findings of this research project this can be inferred that the biological attributes and composition of the selected plant EOs not only varied within the plant species but also in relation to the two isolation techniques employed (P<0.05). Overall, the SCF extracted essential oils were found to be superior to the hydro-distilled essential oils in terms of antioxidant and biological attributes studied. It can be accepted that the essential oils from the selected medicinal plants of Soon Valley are good source of biologically active components and possessed appreciable antioxidant and other biological activities thus supporting their potential utilization as components for the functional food, pharmaceutical and nutraceutical applications. In this direction, further studies can be conducted in future towards evaluation of broader spectrum antioxidants using in-vivo trials.