Effect of organic and inorganic zinc foliar application on the natural product composition and antioxidant activity of lemon balm (Melissa officinalis)

Lemon balm (Melissa officinalis L.) is known as one of the most important hormonal plants (anti-thyroid), sedative, wound healing agents, and flavorings in the food industry. The present work aimed to determine the effect of different zinc (Zn) sources on the natural product composition, and antioxidant activity of lemon balm. The experiments were performed in a greenhouse in Eram Garden (Shiraz, Iran) with three replications and five different treatments including T1: No zinc (control(, T2: EDTA-chelated Zn, T3: nano Zn, T4: Zn sulfate, and T5: citrate-chelated Zn. The results showed that all Zn resources improved the chemical composition of the lemon balm essential oil (EO), such as geranial, caryophyllene oxide, and phthalic acid. The highest amount of geranial (40.8%) was achieved in the plants treated with citrate-chelated Zn. The highest total content of caryophyllene oxide (8.8%) was achieved when Zn sulfate was applied. The highest phthalic acid (2.24%) was obtained in the plants treated with Zn sulfate and nano Zn. The highest antioxidant activity (162.86 mg L^-1) was found when nano Zn was applied. The results revealed that the application of Zn to therapeutic plants like lemon balm could be very useful for the production of active natural compounds such as geranial, phthalic acid, and caryophyllene oxide for use in drug industries and medical materials.