Essential oils are secondary metabolites formed in aromatic plants. They are volatile, terpenoids, and usually isolated by distillation methods. They have odor and several pharmaceutical, medical, and biological properties such as antiseptic, bactericidal, virucidal, and fungicidal, as well as against liver and lung carcinogenesis, colon tumors, and gastric cancer (Davis 1982; Yeung 1999; Khursheed et al. 2016). The Administration of Food and Drug (FDA) indicated that EO of citrus is safe natural product, so it can be added to canned food and cosmetics to prevent the propagation of pathogens and spoiling microorganisms (Fisher and Phillips 2006; Nannapaneni et al. 2009; Velázquez-Nuñez et al. 2013). The residues of different organs of citrus tree such as peels, leaves, and flowers that are produced after juice extraction, pruning of branches and change to precipitation flowers are very important sources of EO (Viuda-Martos et al. 2009), as well as citrus residues which can serve as raw material for the extraction of EOs needed for various domestic and industrial uses (Giwa et al. 2018). Sweet lemon (Citrus limettioides Tan.), one of the citrus species, belongs to family Rutaceae. Just one literature was carried out in México to isolate and characterize the constituents of sweet lemon EO that was isolated from peels and leaves (Pino et al. 2010); this study reported that different variations were observed in the chemical constituents due to the differences in plant organs, and the major component of peel EO was limonene while the main constituents of leaf EO were limonene, citronellal, and linalool.
The yield and chemical constituents of EO can be changed by various conditions such as fertilizers, irrigation, climate, location, plant organ, and others (Krayni et al. 2015). The highest yield of EO and major constituents (thymol and carvacrol) of thyme were detected in the EO isolated from the aerial parts during the flowering stage (Jordan et al. 2006; Nejad-Ebrahimi et al. 2008; Omidbaigi et al. 2010). Different changes were recorded in the composition of oregano (Origanum onites) EO due to various plant organs (Kizil et al. 2008). The EO extracted from Eucalyptus cinerea fruits produced higher amount of 1,8-cineole (81%) than that isolated from leaves (75%) and flowers (78.8%) (Silva et al. 2011). The EO of Sodom apple extracted from the leaf, stem, flower, and fruit was analyzed by GC/MS (Wahba and Khalid 2018); leaf EO resulted in the highest values of E-phytol, myristicin, myristic acid, oxygenated sesquiterpenes (OS), and oxygenated diterpenes (OD); fruit EO recorded the greatest amounts of E,E-farnesyl acetone, monoterpene hydrocarbons (MH), oxygenated monoterpenes (OM), and sesquiterpenes hydrocarbons (SH). The EO components of Sarcopoterium plants were evaluated by Sipahi et al. (2017); the major components of EO isolated from the stem were aldehydes (40%), aromatic constituents (34.0%), and OM (21%); aldehyde component (43%), OS (26%), and aliphatic hydrocarbons (21%) were detected as the main components in leaf EO, while aldehydes (52%) and aromatic components (48.4%) were identified as the main constituents of root EO.
There are no investigations on the EO composition of sweet lemon extracted from various part residues (leaves, flowers, peels) in Egypt, so the aim of this study was to describe the composition of sweet lemon EO extracted from different residues. This study may increase the sources of natural products (EO) used in food and drug industries.