Melissa officinalis extracts obtained using maceration, ultrasoundand microwave-assisted extractions: Chemical composition, antioxidant capacity, and physical characteristics

Even though Melissa officinalis L. (lemon balm, fam. Lamiaceae) is a well-known medicinal, aromatic, and spicy plant, and its physicochemical profile and biological activity have been investigated, there is no detailed research regarding the influence of solvent nature (polarity) on the extraction of active compounds (total polyphenols and total flavonoids) and antioxidant activities of the obtained extracts. Therefore, this study aimed to evaluate the polyphenol and flavonoid contents, as well as the antioxidant potential of lemon balm extracts obtained by varying the polarity of the extraction solvents (methyl alcohol, acetone, ethyl acetate, and deionized water) and using three extraction techniques (maceration-MAC, ultrasound-UAE, and microwave-assisted extraction-MAE). Two in vitro tests (ABTS and FRAP assays) were used to determine the antioxidant activity of the extracts. Total tannin and total protein contents, extraction yield, and physical properties of the selected extracts were measured as well. The highest content of polyphenols was found for the methanolic and water extracts obtained by all three extraction techniques, while the highest flavonoid yield was detected only in the mentioned methanolic extracts. The microwave reactor provided methanolic, ethyl acetate, and water extracts with the highest ABTS radical scavenging activity, while in the case of UAE, it was methanolic and water extracts, and in the case of MAC only water extracts. On the other hand, among lemon balm extracts from MAC, water extract possessed the highest ferric reducing power, whereas in UAE and MAE, it was ethyl acetate extract. Total tannin content determined in selected water extracts was 2.55, 4.53, and 1.83 mg tannic acid equivalent (TAE)/mL, while total proteins amounted to 1.34, 1.50, and 1.31 mg/mL using MAC, UAE, and MAE, respectively. The content of total extractive substances in the form of the extraction yield was also determined for selected water extracts and amounted to 12.6 % for MAC, 17.2 % for UAE, and 36.8 % for MAE. Further, this research has included the investigation of some physical properties of lemon balm water extracts, such as conductivity (3.68-4.14 mS/cm), pH (5.99-6.43), density (0.854-0.901 g/mL), surface tension (26.0-31.7 mN/m), and viscosity (1.18-1.21 mPa·s). This research represents the base for the future encapsulation of lemon balm extracts, enriched in polyphenol content, in a novel type of biofunctional carrier that potentially can be applied in the pharmacy, chemical industry, and biotechnics.