Untargeted metabolomics and targeted approach of essential oils to differentiate five Ocimum species using gas chromatography coupled with mass spectrometry

The chemical profile of essential oils (EOs) obtained from Ocimum species can be used to identify species and assess the potential applications for them. Some kinds of basil (Ocimum L.) are used as medicinal herbs because of the distinct biological activity of their essential oils. The goal of this study was to use chemometrics to distinguish between five closely related species of Ocimum, viz., O. basilicum Linn., O. canum Sims., O. citriodorum, O. gratissimum Linn. and O. sanctum Linn. to distinguish between different volatile organic compounds (VOCs) based on their EOs. Through the use of gas chromatography-mass spectrometry (GC-MS) operated under screening mode to determine the compositions of the EOs, total 119 metabolites were found. The VOC composition of the investigated species allowed for distinct differentiation, as demonstrated by untargeted metabolomics and multivariate analysis using Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA). Simultaneously using GC-MS selected ion monitoring (SIM) method was established for the simultaneous four major components like Linalool, Caryophyllene, Estragole and Eugenol of quantitative estimation in five different Ocimum species, as well as providing methodological reference for quality control. Based on chromatographic data, Principal Component Analysis (PCA) and Hierarchical Clustering Analysis (HCA) heat map experimental design were able to successfully distinguish between the five related species. The content was detected in varying proportions between batches of the same species, according to quantitative evaluation i.e., (i) Three different of batches Ocimum basilicum Linn., Estragole was 52.9 %w/w as higher content, Linalool 18.19 %w/w, Caryophyllene 0.3 %w/w, and Eugenol were not detected, (ii) Three different of batches Ocimum canum Sims., Linalool was founds as > 70.82 %w/w as higher content, Caryophyllene 3.41 %w/w, Eugenol 0.8 %w/w and Estragole were not detected in all three different batches, (iii) Three different of batches Ocimum citriodorum., Caryophyllene was found around 34.36 %w/w, Linalool 6.29 %w/w; Eugenol 10.64 %w/w and Estragole were not detected in all three different batches, (iv) Ocimum gratissimum Linn., in three different of batches, Eugenol was found in high content up to 65.77 %w/w, Linalool 1.77 %w/w respectively, Caryophyllene 10.8 %w/w and Estragole not detected in all three different batches, (v) Ocimum sanctum Linn., Eugenol were in high content at 57.21 %w/w, Caryophyllene up to 19.85 %w/w, Linalool and Estragole both were not detected in all three different batches; this could be because of the species nature and the varying climatic circumstances. Ocimum essential oil is a potent antibacterial, antioxidant, repellent, insecticidal, larvicidal, nematocidal, and therapeutic agent (anti-inflammatory, antinociceptive, antipyretic, analgesic, immunomodulatory, etc.) with a vast range of biological action.