**1. Introduction**

Olive oil is one of a great interest in the vegetable oils world market. It is produced from the fruit of olive (*Olea europaea* L.). Virgin olive oil (VOO) is obtained exclusively by mechanical cold extraction [1]. It is not subjected to any chemical treatments apart from washing, decantation, centrifugation, and filtration. These processes may be carried out without refining, which makes the obtained oils highly appreciated by consumers thanks to their rich nutritional value, several health benefits, and unique organoleptic properties. Olive oil organoleptic and nutritional characteristics arise from noble compounds it contains. VOO composition consists of an unsaponifiable fraction (1 to 2%) along with essential unsaturated fatty acids contained in glyceridic

#### **Figure 1.**

*Publication trends of olive oil composition (based on data retrieved from Scopus database).*

fraction (98 to 99%) [2]. The composition of olive oil is well outlined in the literature. An updated analysis of the composition of olive oil reported in the literature is shown in **Figure 1**. In fact, on November 29th, 2021, the Scopus database was chosen to search for peer-reviewed literature regarding olive oil composition. The search string: ("olive oil\*" AND "composition\*") was utilized to extract bibliometric information from the Scopus online database. A total of 2980 publications were recovered through the literature search within the range of years from 2010 to 2021, 1892 of them representing about 65% are published in the interval of years from 2015 to 2021 (**Figure 1**).

## **2. Olive oil extraction technologies**

Olive oil is made from fresh olives, which are extracted by mechanical processes [3]. Olive oil extraction technologies are summarized in **Figure 2**. There are two main olive oil extraction processes: traditional oil mills, and a relatively new extraction process known also by continuous mills and characterized by two or three phases [4, 5] **Figure 2**. All the above processes aim at separating the liquid oil phase from the other constituents of the fruit [6]. Likewise, olives should be processed as rapidly as possible after harvesting to reduce oxidation and preserve their quality [7].

Concerning the traditional press method, olive fruits liberated from leaves are washed, crushed using mill stones, and malaxed into a paste containing solid matter (core debris, epidermis, cell walls, etc.) and fluids (oil and vegetation water contained in the cells of olives). This is then spread on spherical mats [6]. Pressure with a hydraulic piston press is exerted then to obtain, firstly, a solid fraction (known as pomace) and, secondly, the mixture of oil and water is filled into a container and, eventually, the oil and water are then separated by gravity and collected through decantation [5]. The pressing process is the oldest method of obtaining olive oil [8]. Owing to lower production efficiency and high labor costs, during the last decade, the discontinuous pressing systems have widely been substituted by continuous systems, along with the development of centrifuge technology [4, 9]. After the steps of washing, crushing, and *Olive Oil: Extraction Technology, Chemical Composition, and Enrichment Using Natural… DOI: http://dx.doi.org/10.5772/intechopen.102701*

**Figure 2.**

*Scheme of discontinuous and continuous extraction systems. OMWW = olive mill wastewater.*

mixing, the mechanical extraction of the oil occurs mainly by a continuous process based on centrifugation using a decanter. The decanter centrifuge is equipped with a rotary bowl as well as a screw conveyor, which allows the processing of great quantities of olives in a short time [7]. Continuous separation systems can be divided into twophase and three-phase systems, based on the decanter type used and the level of the phase of separation [9]. In the three-phase process, an additional amount of hot water is added to wash the oil, and then the three-phase decanter (insoluble solids, oil phase, and an aqueous phase), are separated following their density [7, 10]. Firstly, the solid wastes (insoluble solids), are separated from the remaining two phases in the decanter, and the liquid phases (oil phase as well as aqueous phase), are then subjected to vertical centrifugation to separate the olive oil from the olive mill wastewater [7].

Owing to the significant issue of wastewater produced, this three-phase system is preferred over the two-phase system since it is more eco-friendly [11]. This latest uses only a semi-liquid slurry (vegetation water along with insoluble solids) phase and the oil phase, a semi-liquid slurry, which is also known as two-phase olive mill waste [7]. This process has a reduced environmental impact owing to the reduced requirement of water as well as the amount of waste produced [7].
