Biological value and essential oil composition of two Monarda species flowers

In this study the quantity of the main nutritional and bioactive compounds, as well as the antioxidant activity (DPPH, FRAP and ABTS methods) and essential oil composition of Monarda fistulosa L. and Monarda citriodora subsp. austromontana Cerv. ex Lag. ‘Bees’ Favourite’ flowers were investigated. The field experiment was carried out for three years (2014–2016) and the laboratory analyses in the years 2015–2016. The obtained results showed that M. citriodora flowers were characterized by a dry matter (22.42%), total ash (1.86% FW), crude fibre (4.89% FW), sucrose (0.31% FW), total flavonoids (0.795% DW) and antioxidant activity in FRAP test (7.96 mg TE g⁻¹ FW), while M. fistulosa showed the highest values of total sugars/titratable acidity ratio (4.05), antioxidant activity in DPPH test (7.35 mg TE g⁻¹ FW) and contents of reducing sugars (1.46% FW), total chlorophyll (401.10 μg g⁻¹ FW), chlorophyll a (271.74 μg g⁻¹ FW) and b (92.07 μg g⁻¹ FW), L-ascorbic acid (48.99 mg 100 g⁻¹ FW) and total polyphenols (7.64 mg GAE g⁻¹ FW). The essential oils were obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC-MS). The main compounds of M. fistulosa oil were carvacrol (28.16 and 23.66% in 2015, and 2016, respectively), p-cymene (20.10 and 17.94%), thymoquinone (12.60 and 16.30%) and γ-terpinene (8.72 and 4.07%), whereas linalool (34.86 and 26.96%), thymol (17.83 and 37.34%), β-thujene (6.12 and 2.00%) and camphene (5.80 and 5.64%) were the major constituents of M. citriodora Cerv. ex Lag. ssp. austromontana ‘Bees’ Favourite’ oil.