The extraction method determines the chemical profiles of leaves and stems of Melissa officinalis L.

Context: Melissa officinalis L. is widely used in herbal medicine, primarily for its phenolic compounds, especially rosmarinic acid. While the leaves are commonly used in extemporaneous preparations, stems are often discarded as waste. Aims: To investigate how different extraction methods affect the chemical profile of M. officinalis leaves and stems, and to assess whether stems contain bioactive compounds that are typically attributed to the leaves. Methods: Infusions and ultrasound-assisted sequential extractions using hexane, ethyl acetate, and ethanol were performed on dried stems and leaves. Extracts were analyzed by HPLC-MS/MS, and the resulting data were processed using MZmine and evaluated by multivariate statistical tools (PCA and PLS-DA) through MetaboAnalyst. Results: Infusion extracts revealed marked chemical differences between leaves and stems, with rosmarinic acid absent in stem preparations. However, ultrasound-assisted extraction using polar organic solvents revealed a comparable chemical profile between both organs, including the presence of rosmarinic acid. PCA and PLS-DA confirmed these differences and similarities depending on the extraction method applied. Conclusions: The findings demonstrate that the extraction technique critically determines the chemical profile of M. officinalis, especially for identifying key bioactive compounds. Ultrasound-assisted extraction enables the recovery of important metabolites from plant parts commonly regarded as waste, promoting more sustainable and efficient use of medicinal plants.