Enrichment of antioxidant compounds from lemon balm (Melissa officinalis) by pressurized liquid extraction and enzyme-assisted extraction

In this work enzyme-assisted extraction (EAE) and pressurized liquid extraction (PLE) are applied for extraction of natural compounds from lemon balm (Melissa officinalis). Cellulase, endo-β-1,4 xylanase and pectinase were studied in order to degrade cell wall of lemon balm leaves and to release phenolic compounds. On the other hand, in order to compare the performance obtained with EAE, PLE using water and ethanol was employed maintaining 150 °C as extraction temperature. The obtained extracts were characterized in terms of antioxidant capacity by using DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging and trolox equivalent antioxidant capacity (TEAC) in vitro assays, whereas the Folin–Ciocalteu procedure was employed to estimate the total phenols content. On the other hand, extracts were chemically characterized by liquid chromatography tandem mass spectrometry (LC–MS/MS). The results showed that EAE enhanced the total phenolic content and the antioxidant capacity compared to a non-enzymatic control. PLE extracts presented higher amount of phenols and antioxidant capacity than enzyme-assisted extracts, reaching the highest values on water extracts (193.18 mg gallic acid/g extract and EC50 = 6.81 μg/mL). Among the bioactive phenolic compounds identified in lemon balm, rosmarinic acid was the main component, although other important compounds were also identified, such as caffeic acid derivatives (salvianolic acids, lithospermic acid) and rosmarinic acid derivatives (rosmarinic acid hexoside, sagerinic acid, sulfated rosmarinic acid). The present study confirms that EAE and PLE can be considered alternative methods for the extraction of natural compounds with biological activity from natural sources.

► EAE and PLE are employed for the first time to obtain antioxidant compounds from lemon balm.
► Enzyme treatment increases the extraction of total phenols and antioxidant capacity of extracts.
► PLE allows extracting more efficiently phenolic compounds from this sample.
► LC–MS/MS is employed to identify a diverse group of phenolic compounds present on the extracts.