The Influence of Abiotic Factors on the Yield and Composition of the Essential Oil of the Mastic Tree (Pistacia lentiscus L.) Leaves

This study evaluated the effects of abiotic factors and extraction conditions on the yield, chemical composition, and antimicrobial activity of essential oil (EO) from Pistacia lentiscus L. leaves collected at four Adriatic locations during three phenological stages. Steam distillation was performed at 0.3, 0.7, and 1 bar. EO yield increased significantly with pressure, reaching a maximum at 1 bar, while the flowering stage provided the highest yields overall. Leaves from Vela Luka produced the highest EO yield, whereas Pag samples yielded the least. GC–MS analysis identified 56 components, accounting for 99.19–99.99% of total EO, with α-pinene, limonene, myrcene, and β-pinene as the dominant constituents, confirming a monoterpene-rich chemotype. All EO samples showed low but measurable inhibitory activity against Escherichia coli AB1157 and Erwinia amylovora EaED, as assessed by the disk diffusion method. Pearson correlation and PCA analyses indicated a positive association between monoterpene content and inhibition zone diameter against E. coli, and a positive association between monoterpene alcohol content and inhibition against E. amylovora. As antimicrobial activity was assessed exclusively by the disk diffusion method, the present findings may serve as an indicative basis for future investigations into the relationship between EO chemical composition and antimicrobial potential, and they require validation through quantitative, standardized antimicrobial testing.