Bioactive Compounds and Antioxidant Activity in Lemon Balm (Melissa officinalis L.) Grown Under Different Growing Conditions

The aim of this study was to evaluate the bioactive compounds and antioxidant activity of lemon balm (Melissa officinalis L.) grown under two farming systems (conventional vs. organic farming). From the content of photosynthetic pigments, total phenolics, and total flavonoids, as well as individual phenolic acids and flavonoids, the antioxidant potential was evaluated in 95% and 50% ethanol extracts. Moreover, GC-MS analysis of lemon balm essential oils was used to reveal the detailed composition. Forty-three compounds were detected in the essential oil from organic farming lemon balm, representing 99.70% of the total content. Among these, several compounds, such as α-pinene, n-octan-3-ol, bergamal, trans-rose oxide, dihydro-linalool, cis-isocitral, and trans-anethole, were found exclusively in the organic essential oil. In comparison, thirty-six compounds were detected in the essential oil from conventionally grown plants, representing 99.80% of the total content. The organically grown lemon balm demonstrated higher values of phenolics, flavonoids and antioxidant activity in comparison to the conventional ones. The levels of natural pigment were more than twice as high in the conventionally grown samples. Moreover, the 50% ethanol extracts contained 1.5 to 2 times more phenolic compounds with the highest antioxidant potential by the CUPRAC method. A positive linear correlation (r2 = 0.98) was found between total phenolics and electron transfer-based antioxidant methods. Therefore, the organic farming led to the production of lemon balm with more secondary metabolites, such as phenolic acids and flavonoids, with higher antioxidant activity.