Ocimum Gratissimum essential oil: A review of extraction methods, phytochemical constituents, pharmacological uses and formulation approaches

Abstract

Ocimum gratissimum is a plant native to Africa. Its leaves have been used in local dishes over the years, with documented evidence of varying pharmacological uses of its essential oil. This review focuses on the extraction methods, phytochemical constituents, pharmacological uses and formulation approaches of Ocimum gratissimum essential oil. The traditional extraction methods that have been widely used include the solvent, cold press and hydrodistillation methods. However, newer methods such as steam distillation, ultrasound and microwave assisted hydrodistillation, supercritical fluid extraction, pressurized liquid extraction and pressurized hot water extraction methods have not been fully reported. These methods provide more yield of the essential oil compared with the traditional methods and their processes are less laborious. Furthermore, they are often limited to analytical applications as they cannot handle large quantities of samples. The phytochemical constituents of Ocimum gratissimum essential oil vary, based on location of the plant and the time of the season the plant parts were harvested for extraction. The African species have more thymol than eugenol. Other notable constituents are saponins, terpenes and flavonoids in both African species and others. The essential oil of Ocimum gratissimum bears the scent of the plant and other important properties such as protection of the plant from pests and to attract insects for cross-pollination. The essential oil of this plant has been noted to possess various pharmacological properties which explains its use in inflammatory conditions and the treatment of diarrhoeal disease, wound healing and cerebrovascular disorder, amongst others. The essential oil of Ocimum gratissimum has been embedded in gels, cream, silver nanoparticles and nanoemulsion to improve its pharmacological activity and bioavailability. This review article highlights the potentials of the essential oil of this ubiquitous plant as a therapeutic source for the treatment of different tropical diseases.