Chemical Composition and Antimicrobial Activity of Essential Oil from Seeds of Pimpinella heyneana

Published in Khimiya Prirodnykh Soedinenii, No. 4, July–August, 2022, pp. 637–638.

Apiaceae is one of the largest flowering plant families of angiosperm having more than 3700 species in 434 genera [[1]]. The members of this family are mostly native to the tepid climate region of the northern hemisphere and are often used for several medicinal applications [[2]–[5]]. The plant species in the Apiaceae family are often rich in essential oils, which is one of the pivotal reasons for the pharmaceutical importance of many of the apiaceous drugs. There are several plant species from the Apiaceae family that have been explored for essential oils, among them, the plant species belonging to the Pimpinella genus have attracted considerable attention due to their ethno-pharmaceutical history [[4]–[7]]. More than 150 species under this genus are distributed throughout Asia, Europe, and Africa [[6], [8]]. Still, there are a lot of species under this genus that are yet to be explored for their pharmaceutical activities. In India, Western Ghats has become a hot spot for a number of different plant species that are yet to be explored. One of such unexplored plant species, Pimpinella heyneana is indigenous to India and has been mainly used in folk medicine. There is some evidence in ethnomedicine where different parts of Pimpinella heyneana have been used for various medicinal applications such as gum swelling, gas flatulence [[10]], and diarrhoea [[12]]. Despite ethno-pharmaceutical evidence, no information is available on the content and composition of the essential oils of Pimpinella heyneana. In this context, the present study mainly focuses on identifying phytoconstituents present in essential oils extracted from Pimpinella heyneana seeds by using GC-FID, GC-MS, and its antimicrobial activity against gram-positive and gram-negative bacteria.

The herb of Pimpinella heyneana Wall. was collected from North Western Ghats (Nashik District, Maharashtra, India) in October 2019. The plant was authenticated by the plant taxonomist Dr. Ravikiran Pagare at Sandip University, Nashik, India, and the herbarium was assigned to voucher specimen No. SUN20190001. The collected plants were dried in the shade. After drying, the seeds were collected and filtered to remove any unwanted materials. As per the conditions of Indian Pharmacopoeia, seeds (100 g) of P. heyneana were subjected to hydrodistillation for 6 h in a Clevenger-type apparatus. The collected oil sample was dehydrated over anhydrous sodium sulfate and stored in sealed vials and protected from the light at 4°C before analysis. After removing water droplets from the extracted oils, it appeared colourless with a characteristic odour. The average yield of the essential oil was found to be 1.8% v/w. The volatile bioactive compounds present in essential oil were identified by GC and GC-MS analysis. The essential oil elements were identified by reference to a homologous series of normal alkanes (C8–C40) as well as by comparison of their mass spectral fragmentation patterns with those recorded in the literature and retention index-based similarities search stored in the MS Library (NIST/EPA/NIH Mass Spectra Library 2017). GC analysis of the essential oil was performed on Thermo Scientific (Trace-1110) gas chromatography coupled with an FID detector as well as equipped with a TG-5MS silica column (30 m × 0.25 mm, 0.25-μm film thickness). GC-MS analysis was performed on Shimadzu GCMS-QP Series, Model GCMS-QP2020 with Sh-Rxi-5Sil MS capillary column (30 m × 0.25 mm × 0.25-μm film thickness).

Twenty-seven different compounds were detected from the essential oil of P. heyneana. The active compounds along with their retention time, retention index, and content (%) are tabulated in Table 1. The total run time required for complete GC analysis was 46 min and for GC-MS analysis it was 53 min. The fragmentation pattern of compounds obtained in mass spectra was matched with Wiley 9.0 and National Institute Standard and Technology libraries.

Table 1. Phytoconstituents Identified in Essential Oil of P. heyneana Seeds

RI: retention index calculated on Sh-Rxi-5Sil MS capillary column (30 m × 0.25 mm × 0.25 μm).

Of the 27, allyl tetramethoxy benzene (51.7%) and myristicin (27.2%) were the major compounds, while the minor compounds were tyranton (5.9%), eudesma-4(14),11-diene (2.7%), elemicin (2.3%), apiol (2.1%), borneol acetate (1.5%), and α-selinene (1.2%). In addition to these, monoterpene along with its esters and sesquiterpenes were found.

The antimicrobial activity of essential oil was performed using the agar disk diffusion method. It was observed that the extracted oil showed inhibition against both gram-positive microorganisms, i.e., Staphylococcus aureus and Bacillus subtilis, and the one gram-negative microorganism, i.e., E. coli. The essential oil did not show any effect against Pseudomonas aeruginosa (Table 2). The antibacterial activity of the oil may be attributed to the presence of phenylpropanoid derivatives at a high percentage.

Table 2. Antimicrobial Activity of the Essential Oil of P. heyneana Seeds Expressed as Diameter of Zone of Inhibition, mm

Diameter in mm calculated by Vernier Caliper; Values are given as mean ± SD. NCIM: National Collection of Industrial Microorganisms. N.a.: no zone of inhibition; the undiluted samples were tested, standard – chloramphenicol.