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1. Introduction
The scientific name of lemon verbena is Lippia citriodora and it belongs to the Verbenaceae family. The genus Lippia includes approximately 200 species of herbs, shrubs and small trees which are spread widely in South America, Central America and Ttropical Africa (Pascual et al. , 2001; Terblanche and Kornelius, 1996). It is native in South America in Chile, Argentina, Peru and Uruguay and was transported to Europe at the end of the seventeenth century, spreading in southern Europe, especially Italy and Spain and in South Africa, particularly Morocco. Lemon verbena is used in folk medicine for the treatment of asthma, spasms, cold, fever, flatulence, colic, diarrhea, indigestion, insomnia and anxiety (Hellemont, 1986; Newal et al. , 1996; Graça et al. , 1996); it is also recommended as an analgesic, anti-inflammatory and antipyretic (Pascual et al. , 2001). It is believed that these properties are due to its essential oils and polyphenols (Carnat et al. , 1999; Santos-Gomes et al. , 2005), and its sedative and analgesic properties are due to the presence of verbascoside, which is present as one of the most important and major polyphenols (phenylpropanoids) in lemon verbena tea (Nakamura et al. , 1997). As reported, it is used in the treatment of Alzheimer's disease due to the presence of luteolin 7-diglucuronide as the major flavonoid compound (Sawmiller et al. , 2014; Carnat et al. , 1995). It is also used in the perfume industry and in food additives and flavoring beverages (Pascual et al. , 2001).
Published studies have shown the richness of lemon verbena leaf's infusion of polyphenols, especially phenolic acids, phenylpropanoids and flavonoids (flavones), which have antioxidants and scavengers of free radicals (Choupani et al. , 2014; Shahi et al. , 2014; Vinha et al. , 2013; Portmann et al. , 2012; Bilia et al. , 2007; Carnat et al. , 1999; Skaltsa and Shammas, 1988). According to the authors' knowledge, no one has previously studied the difference in the total content of phenols and flavonoids in lemon verbena leaf infusions during growth stages. However, lemon verbena was cultivated in Syria and used in folk and Arabian medicine, so the aim of this research is to compare and determine the total content of phenols and flavonoids of...