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.