Phenolic composition and antioxidant properties of some traditionally used medicinal plants affected by the extraction time and hydrolysis.

Polyphenolic phytochemicals in traditionally used medicinal plants act as powerful antioxidants, which aroused an increasing interest in their application in functional food development. The effect of extraction time (5 and 15 minutes) and hydrolysis on the qualitative and quantitative content of phenolic compounds and antioxidant capacity of six traditionally used medicinal plants (Melissa officinalis L., Thymus serpyllum L., Lavandula officinalis Miller, Rubus fruticosus L., Urtica dioica L., and Olea europea L.) were investigated. The content of total phenols, flavonoids, flavan-3-ols and tannins was determined by using UV/Vis spectrophotometric methods, whilst individual phenolic acids, flavones and flavonols were separated and detected by using HPLC analysis. Also, to obtain the relevant data on the antioxidant capacity, two different in vitro assays (ABTS and FRAP) were used. The extraction efficiency of phenolics, as well as the antioxidant capacity of plant extracts, was affected by both prolonged extraction and hydrolysis. The overall highest content of phenolic compounds was determined in hydrolized extract of blackberry leaves (2160 mg GAE/L), followed by the non-hydrolized extract of lemon balm obtained after 15 minutes of extraction (929.33 mg GAE/L). The above extracts also exhibited the highest antioxidant capacity, while extracts of olive leaves were characterized with the lowest content of phenolic compounds, as well as the lowest antioxidant capacity. The highest content of rosmarinic acid, as the most abundant phenolic compound, was determined in non-hydrolized extract of lemon balm, obtained after 15 minutes of extraction. The distribution of detected phenolic compounds showed a wide variability with regard to their botanical origin. Examined medicinal plants showed to be a valuable supplement to a daily intake of bioactive compounds.