Cold pressing
Cold pressing is an extraction traditional method specific to citrus species (orange, bergamot, grapefruit, lemon, etc.) to produce essential oil. During extraction, the oil glands break and release the volatile oils. The oil glands are located in the fruit rind or outside of the mezocarpe. Figure 5 shows a cross section of a citrus fruit (figure 5). This method is also called Expression [9, 22, 39]. In this physical method, at first, the rinds of the fruits are crushed, then ground and pressed to release the volatile oils in the skin. In this section, a mixture of water and oil is produced simultaneously. Finally, the mixture is allowed to settle. Then the collected oil is washed with water and separated by centrifuge [40]. The figure 6 represents a schematic of the cold pressing [22]. Today the systems of cold pressing can be classified into four categories: ”sfumatrici” machines and ”speciale sfumatrici”, ”Pellatrici” machines, ”FMC whole fruit process” and ”Brown oil extractors (BOEs)” [9,41].
Soto et al. [42] used an enzymatic hydrolysis combined with cold pressing to obtaining borage (Borago officinalis) seed oil for better yield. while Anwar et al. [43] studied the effect of different enzyme on the yield of cold pressing and showed this system has higher yield in compare to without the enzyme.