Untargeted metabolomics approach of essential oils to differentiate five Ocimum species and their anti-choline-sterase and anti-tyrosinase activity

Abstract

Chemical profiling of essential oils (EOs) from Ocimum species can lead to species identification and the valorization of their potential use in the food and flavour industries. This research was undertaken to discriminate chemometrically between five very closely related species of Ocimum, viz., O. tenuiflorum (green basil), O. tenuiflorum (purple basil), O. gratissimum, O. kilimandscharicum, and O. basilicum, based on their leaf EOs, to identify the differential volatile organic compounds (VOCs), and to determine their anti-cholinesterase and anti-tyrosinase activities. The leaf EO compositions were determined using GC-MS, and a total of 67 metabolites were identified. Untargeted metabolomics and multivariate analysis showed clear discrimination among the studied species based on their VOCs composition. PLS-DA (Partial least squares-discriminant analysis) identified the characteristic VOCs responsible for discrimination among the species. Based on VIP scores, the top 10 metabolites for discrimination among the selected species were detected, viz., linalool, α-cadinol, γ-murrolene, β-ocimene, α-eudesmol, γ-eudesmol, α-selinene, E-β-farnesene, humulene epoxide II and linalyl acetate. The quantification (mg/μL) of eugenol, β-caryophyllene, linalool, β-ocimene, and neo-allo-ocimene of the isolated leaf EOs were done by comparing with the standards. O. basilicum showed the highest AChE inhibitory activity whereas, O. tenuiflorum (green basil) showed the highest tyrosinase inhibition. These results led to the conclusion that the EOs of edible Ocimum species exhibit important enzyme inhibitory activities and can be potential sources of natural active ingredients for memory-enhancing as well as progressive neurodegenerative disorders and also as non-toxic skin lightening and anti-browning agents for fruits, vegetables, and other food substances.