Effect of harvest date on yield and secondary compounds of lemon balm (Melissa officinalis L.)

The quality of the drug of lemon balm (Melissa officinalis L.) is influenced by several factors, among which the effect of ontogenesis has practically not been studied before. Five varieties ('Lorelei', 'Lemona', 'Quedlinburger Niederliegende,', 'Gold Leaf', 'Soroksar') were sampled at vegetative, budding, full flowering and after flowering phases at two locations (Budapest and Poznan) and their dried leaves analysed. The accumulation of volatile compounds showed maximum values (0.08-0.46 ml/100 g dry weight) in budding phase (Budapest) or during flowering (Poznan). The content of total phenolics was highest (226-431 mg gallic acid equivalent/g dry weight) in vegetative stage and in some cases similar values were measured until budding. After a sharp decrease at flowering time in several cases, a second peak was detected at the end of the vegetation period. Similarly to the total phenolics, also the total flavonoid content reached the highest level (0.239-1.152% dry weight) at the first half of the vegetation period however, with characteristic differences between habitats. In cultivation, the highest essential oil content may be reached later than highest polyphenol content, however harvesting at budding time may assure a good quality from both aspects with advantageous fresh and drug yields. The described dynamics of the accumulation of the investigated secondary metabolites was depending more on the habitat and less from the cultivar.