GC-MS Analysis and Antimicrobial Activity of the Essential Oil of Trunk Exudates of Pistacia atlantica var. mutica

The genus Pistacia L. consists of 11 species, most of which are known to produce oleoresin. There are three kinds of pistachio in Iran, including P. vera, P. atlantica, and P. khinjuk. Four subspecies or varieties have been identified for P. atlantica: cabulica, kurdica, mutica, and atlantica [1]. P. atlantica var. mutica is native to a number of temperate countries in Asia. In Iran, this plant grows in the central, western, and eastern regions. The oleoresin of P. atlantica var. mutica, known as “Turk terebinth gum,” is used to make chewing gum in Iran. Mastic gum has been used in traditional medicine for various gastrointestinal disorders like gastralgia, dyspepsia, and peptic ulcer. Mastic gum has been reported to possess considerable in vitro antibacterial and antifungal activity. The total mastic extract without polymer might be effective in reducing Helicobacter pylori colonization as well as in the treatment of cutaneous leishmaniasis. This plant has also been used traditionally as an antiseptic and as a mouth freshener constituent 2 . The essential oil of P. atlantica var. mutica has also potential application as an antimicrobial agent in edible films [2, 3]. The objectives of this study were to report the GC-MS analysis as well as the antibacterial activity of the essential oil of the trunk exudate from Pistacia atlantica var. mutica in order to evaluate its potential application as a natural food preservative. GC-MS analysis has led to the identification of 21 components, listed in Table 1, representing 98.77% of total compounds. The major constituents of the essential oil of mastic gum were -pinene (54.97%), myrcene (11.44%), and limonene (10.08%). A high content of -pinene was also found in the essential oil extracted from the gum of P. atlantica var. mutica [2], P. atlantica var. kurdica [4], P. lentiscus [5, 6], P. khinjuk [7], P. vera [8, 9], and P. terebinthus [10]. A comparison between the results of Delazar [2] and this work shows that -pinene is the main constituent respectively of both essential oils (70.00 and 54.97%). On the other hand, no such similarity was found for the other components. The next two main components reported by Delazar are citral (5.72%) and myrtenol (5.31%), whereas our study showed that myrcene and limonene are ranked as the next two main components (11.44 and 10.08%, respectively). Such variations are most likely related to the geographical origin, harvesting time, growing conditions, as well as extraction method [9]. Disc diffusion is one of the most common assays used in the evaluation of antibacterial activity of essential oils [11]. The results of antimicrobial activity of the essential oil and positive controls are presented in Table 2. The essential oil prevented bacterial growth of all studied bacteria except Pseudomonas aeruginosa. Pseudomonas aeruginosa is considered one of the most resistant bacteria against antimicrobial compounds [12]. Antimicrobial activity analyzed by the disc diffusion method showed that the oil resin of P. atlantica var. mutica was most active against Bacillus cereus, followed by Staphylococcus aureus and Escherichia coli O157 H7. These bacteria are the most common bacteria causing food-borne diseases. With increasing essential oil concentration from 10 to 20 L per disc, antimicrobial activity was also increased. As can be seen, a concentration of 10 and 20 L of the essential oil per disc gives an inhibition zone greater than 7 mm, which is considered as a reasonable limiting inhibition zone for an antibiotic [5]. In the case of Staphylococcus aureus, the clear zones of essential oil were smaller in comparison with those of ampicillin and streptomycin. However, the results of clear zones for Bacillus cereus and Escherichia coli were comparable to positive controls. Finally, gram-positive bacteria (Bacillus cereus and Staphylococcus aureus) were more susceptible to the essential oil as compared to gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa).