Chemical composition, antibacterial and antioxidative activities of Monotheca buxifolia (Falc.) A. DC leaves essential oil

Abstract Monotheca buxifolia (Sapotaceae) is used against different heath aliments due to auspicious biological properties. Essential oil was extracted from leaves of M. buxifolia through steam distillation. Gas chromatography coupled with mass spectrometry (GC-MS) showed presence of 34 compounds. Geranyl acetone (12.6%), nonanal (9.0%) and champhor (8.0%) were abundant while (E)-β-ionone, cis-carvone oxide and caryophyllene oxide were also found. The oil presented 50.2% free radical scavenging activity while total antioxidant potential and total reducing power potential were 40.0 µg AAE/mL and 38.7 µg AAE/mL, respectively. The extracted oil presented moderate activity against Escherichia coli (14 mm) and Bacillus subtilis (11 mm). The study concludes that the essential oil of M. buxifolia leaves has diverse chemical composition and biological activities therefore can be explored for therapeutic potential. Graphical Abstract


Introduction
Volatile compounds have got more attention in recent years due to their ease of extraction, fragrance, and therapeutic potential. Phytochemically, essential oils are constituted by mono, sesqui-terpenes, benzenoids and short chain aromatic and aliphatic alcohols, aldehydes, and ketones. The essential oil interrelates with body by four distinct modes of actions due to presence of aromatic compounds, that is, pharmacological, physiological, psychological, and spiritual (Kaiser 1993).
Monotheca buxifolia (Falc.) A. DC. (family Sapotaceae) is known as Gurgura by local community. The local community uses it as fodder for domestic animals, and as hedge around fields. The wood is also used as roof material (Khan et al. 2011). This plant is used by the local community to cure many diseases, that is, it reduces temperature, works as digestive and laxative agent, provides relief in urinary tract problems, and others (Jan and Khan 2016;Ullah et al. 2017;Khan et al. 2020). Recently, lupeol and benzene derivatives have been isolated from leaves of M. buxifolia (Ali et al. 2021) while many phenolics and flavonoids were identified by HPLC-PDA analysis (Ali, Saleem, et al. 2020).
Here we reported the chemical composition of essential oil extracted from leaves of M. buxifolia. This plant species has not been explored for essential oil composition. The essential oil extracted from leaves was analyzed by GC-MS for the identification of compounds and their percentage composition. Further antioxidant and antibacterial properties of extracted oil were also explored.

Results and discussion
M. buxifolia leaves contained little amount of volatiles constituents. The steam distillation process yielded 0.03% essential oil. Studies have reported low yield of essential oils in many plant species, that is, Azadirachta indica (0.028%), Azadirachta siamensis (0.018%) and Azadirachta excels (0.028%) (Kurose and Yatagai 2005). Likewise leaves of Origanum majorana contained 0.49% while Lantana camara and Nerium oleander have 0.18% and 0.07% essential oil, respectively (El-Seedi et al. 2017). The percentage yield of essential oil is depended on many factors such as climatic and environmental conditions. M. buxifolia wildly grows on dry mountains where water deficient stress imposed by climatic conditions may decrease essential oil content percentage (Petropoulos et al. 2008).
The oil presented moderate (50.2%) DPPH based free radical scavenging activity. Total antioxidant potential and total reducing power potential were 40.0 mgAAE/mL and 38.7 mgAAE/mL, respectively. The oil presented less phenolic contents, 20.8 mg GAE/mL (Table S2). The oil presented moderate antibacterial activity against Gram positive and Gram negative bacterial strains. Maximum zone of inhibition 14 mm was depicted against Escherichia coli while against Bacillus subtilis the average zone on inhibition was 11 mm (Table S2). Biological activities, that is, antibacterial, free radical scavenging, antioxidant and reducing power potential etc. have been reported by polar and non-polar solvents extracts of M. buxifolia Ali, Saleem, et al. 2020;Khan et al. 2020;Ali et al. 2021). The present activities are in line with reported activities and these are due to diversity of biochemical constituents. It has also been reported that Sapotaceae is rich with triterpenes while low amount of saponins and sterol, alkaloids are also present (do Nascimento et al. 2015). Presence of camphor and 1,8-cineole in argan fruit essential oil, also in M. buxifolia leaves, can be the reason that it is used locally as an insect repellent (Harhar et al. 2010). 1,8-cineole has also been reported for antinociceptive, anti-inflammatory antibacterial and antifungal activities (Murata et al. 2013); Camphor retains antidiuretic, antiseptic, anti-infective and anti-seborrheic proctor (Zaidi et al. 2019); Geranyl acetone has anti-psoriatic, antiinflammatory, anti-ulcerative, and anticancer properties (Zhang et al. 2020).

Experimental
The materials used in this study and methodologies followed for extraction, identification, and biological assessment is described in supplementary file.

Conclusion
The study concludes that M. buxifolia leaves oil has diverse phyto constituents and also bears antioxidative and antibacterial properties therefore can be further explored based on traditional therapeutic properties.

Disclosure statement
Authors declare no conflict of interest.

Funding
The research work was funded by Higher Education Commission, Pakistan under Indigenous PhD Fellowship program to Miss Joham Sarfraz Ali.