# Electrospinning of Essential Oils
## 1 Introduction  
Synthetic drugs, preservatives and pesticides used in pharmaceutics, cosmetics, medicine, the food industry and agriculture are a source of health and environmental concerns worldwide [1; 2]. The unregulated and extensive consumption of antibiotics to treat human and animal infections and stimulate the growth of food-producing animals (cattle, pigs, and poultry) has resulted in the emergence of antibiotic resistance in pathogens. The rate of hospitalisation and mortality of patients infected with drug-resistant microorganisms has increased, posing major health threats. lipophilic pesticides, such as organochlorines (OCs), although banned in many countries, are still being applied to eradicate pests [3; 4; 5]. They are hazardous organic pollutants that persist in the environment, bioaccumulate in terrestrial and aquatic ecosystems, and enter the food chain. The exposure to OCs has been linked to acute and chronic diseases in humans, such as type-2 diabetes, Parkinson, and cancer. The potentially disastrous consequences of synthetic chemicals on the global population and the environment have motivated the search for less toxic and more environmentally friendly alternatives. This has seen a renewed interest toward natural products and especially essential oils (EOs) for their antibacterial, antifungal, antiviral, antioxidant, anti-inflammatory, and insecticidal activity [6; 7; 8; 9]. Essential oils are complex mixtures of volatile compounds that are synthesised by plants for defence and signalling purposes [10; 11; 12; 13]. EOs protect plants against herbivores and harmful insects by inhibiting their appetite and attracting their natural opponents. They repel pathogenic microorganisms by targeting their nervous, digestive or endocrine systems, and reducing their growth. EOs promote plant adaptation to abiotic stresses, such as temperature, draught, light, carbon dioxide, and ozone levels, by protecting the photo synthetic apparatus and increasing thermal tolerance of photosynthesis. In addition, they play a crucial role in attracting beneficial animals, such as species-specific pollinators and seed dispersers, to facilitate plant reproduction. The functionality and scent of EOs derive from their main chemical components that belong to the class of isoprenoids and phenylpropanoids [10; 12; 14; 15]. Isoprenoids, also known as terpenoids,are the predominant constituents of EOs and derive from 5-carbon precursors (Figure 1a): isopentenyl pyrophosphate (IPP) and its isomer dimethylallyl pyrophosphate (DMAPP). Higher plants synthesise IPP and DMAPP via two independent pathways: the mevalonic acid (MVA) pathway in the cytosol, and the methylerythntitol phosphate (MEP) pathway in the chloroplasts (organelles used for the photosynthesis) [16; 17]. Phenyltransferase enzymes catalyse the condensation (head-to-tail) of one IPP molecule with one DMAPP molecule to yield geranyl diphosphate (GPP, C\({}_{10}\)), which further condensates with another IPP molecule to form farnesyl diphosphate (FPP, C\({}_{15}\)). The addition of another IPP molecule to FPP gives geranylgeranyl diphosphate (GGPP, C\({}_{20}\)). Then, monoterepne synthases, sesquiterpene synthases, and diterpene synthases convert GPP to monoterepenes (C\({}_{10}\)), FPP to sesquiterpenenes (C\({}_{15}\)), and GGPP to diterpenes (C\({}_{20}\)), respectively. Well-known representatives of terpen are: limonene (found in citrus oils), thymol (found in thymine oil), and menthol (found in mint oil) for monoterepenes; \(\beta\)-caryophyllene (found in clove oil), chamazulene (found in chamomile oil), and \(\beta\)-nerolidol (found in jasmine oil) for sesquiterpenes [18]. Phenylpropanoids are secondary plant metabolites synthetized by the amino acid phenylalanine (primary metabolite) via the general phenylpropanol pathway (Figure 1b) [19; 20; 21; 22]. Their biosynthesis starts with the formation of cinnamic acid from phenylalanine by the action of phenylalanine ammonia-lyase (PAL).