Improvement of Olive Oil Mechanical Extraction: New Technologies, Process Efficiency, and EVOO

 Most of the recent technological innovations applied to the mechanical oil extraction process are aimed at improving virgin olive oil quality and yield. Extra virgin olive oil (EVOO) quality is mainly based on the qualitative/quantitative composition of monounsaturated fatty acids, volatile and phenolic compounds that are strictly related to the health and sensory properties of the product, with particular attention given to the fraction of secoiridoid derivatives and C5 and C6 volatile compounds. The different levels of concentration of these compounds are due to some important variables: agronomic and technological. The chapter explains the recent approaches and innovations introduced in the oil extraction process to improve the working efficiency of the production system and to obtain high‐quality extra virgin olive oils.

Extra virgin olive oil (EVOO) is the main source of lipids in the Mediterranean diet. The marketable, healthy, and sensory quality of an EVOO has been ascribed to the presence of bioactive components such as monounsaturated and polyunsaturated fatty acids (MUFAs and PUFAs), squalene, phytosterols, phenolic, and volatile compounds [15]. Several factors such as the genetic and geographical origin of the olive fruit as well as agronomic practices and technological strategies affect the phenolic content and aromatic profile of EVOO.

Olives, EVOO, and the by‐products of the mechanical extraction system such as olive vegetation water and pomace contain several phenolic compounds with recognized biological and health properties. These substances are considered the principal bioactive compounds of EVOO, showing a high antioxidant activity with an important role in the ratio between EVOO consumption and chronic degenerative events, mainly inflammatory and age‐dependent diseases such as cardio‐brain‐vascular diseases and cancer [411].

Major phenolic compounds found in EVOO are phenolic acids, phenolic alcohols such as tyrosol (p‐HPEA) and hydroxytyrosol (3,4‐DHPEA), hydroxy‐isocromans, flavonoids, lignans, and secoiridoids. This latter class of compounds is represented by the dialdehydic form of decarboxymethyl elenolic acid linked to 3,4‐DHPEA or p‐HPEA (3,4‐DHPEA‐EDA or p‐HPEA‐EDA), an isomer of oleuropein aglycon (3,4‐DHPEA‐EA) and the ligstroside aglycon (p‐HPEA‐EA). They arise from the secoiridoid glycosides (oleuropein, demethyloleuropein, and ligstroside) through the enzymatic action of β‐glucosidase during the mechanical extraction process. Secoiridoids are exclusive compounds of olive leaves, fruits, EVOO, and milling by‐products (olive vegetation water and pomace). The secoiridoid derivatives, along with lignans ((+)‐1‐acetoxypinoresinol and (+)‐1‐pinoresinol), are the most abundant hydrophilic phenols of EVOO [6, 12, 13].

The geographical and genetic origin of olive fruits, the choice of agronomic practices, and the technological conditions of EVOO production affect the wide variability in its phenolic and volatile composition and, therefore, its healthy and sensory quality. The variability range of the content of total phenols and oleuropein derivatives in over 700 industrial EVOO samples analyzed is illustrated in the box and whiskers plots of Figure 1. Based on these results, the contents of the total phenols and oleuropein derivatives show a median of 534 and 398 mg/kg, with values ranging between 187–997 and 77–112 mg/kg, respectively [14].

Health‐promoting effects and organoleptic properties of EVOO have been mainly ascribed to its phenols content (hydroxytyrosol and secoiridoids, in particular) [5, 15]. Several epidemiological studies have in fact fully demonstrated the inflammatory, antioxidant, antimicrobial, anti‐proliferative, antiarrhythmic, platelet antiaggregant and vasodilatory effects of EVOO phenolic compounds [46]. Furthermore, based on scientific evidence, Regulation (EU) No 432/2012 granted the health claim to the EVOO polyphenols, fixing the quantity of 5 mg as the daily amount of hydroxytyrosol and its derivatives (e.g. oleuropein complex and tyrosol) that should be ingested, with a moderate consumption of olive oil (20 g/day) to reduce cardiovascular disease [16].

It has been clearly known that phenolic compounds also have antioxidant activity; therefore, they play a pivotal role in the prolonging of EVOO shelf life [6]. Furthermore, from a sensory perspective, EVOO phenols are the compounds responsible for the characteristic notes of “bitterness” and “pungency”. They stimulate the receptors of taste and the free endings of trigeminal nerve, which elicit the former the bitterness perception, the latter pungency and astringency interaction [15].

Another important part of EVOO flavor is characterized by many different olfactory notes, such as “cut grass,” “floral,” “green apple,” “tomato” and “almond,” which are often related to many volatile substances such as aldehydes, alcohols, esters, and hydrocarbons. In particular, C6 and C5 compounds, especially C6 linear unsaturated and saturated aldehydes, alcohols, and esters, represent the key odorants responsible for those perceptions of positive aroma [1719]. When the olive is intact, the concentration of those volatile compounds is still low. They greatly increase when the cell structures rupture during the mechanical extraction process and with the consecutive activation of the lipoxygenase (LOX). The C6 and C5 compounds are synthesized from linoleic (LA) and linolenic (LnA) acids by the enzymatic activities included in the lipoxygenase (LOX) pathway, and their concentrations depend on the level and the activity of each enzyme involved in this LOX pathway. Figure 2 depicts a schematic illustration of the LOX pathway, which was extensively studied and discussed [18, 19].

However, it is worth mentioning that even though the main pathways are known for the formation of olive oil volatiles, the only correlation that has been proved is that between the “cut grass” aroma and C5 and C6 aldehydes (saturated and unsaturated) [18, 20].

EVOO processing includes a series of mechanical operations for extracting the oil from olive drupes by physical means only, according to Regulation (EU) No 1348/2013 [21]. Among them, the most important as regards quality is the crushing of the olives, which allows the release of the droplets of oil from the vacuoles, breaking down the cellular structure of the olive fruit; the malaxation of the olive paste, which promotes the coalescence of the oil droplets, with the simultaneous release of phenolic compounds into the oil phase and the increase of EVOO aroma; the mechanical recovery of the oil by centrifugation (continuous process) or pressing (discontinuous process); and lastly, filtration, used for removing suspended particles and eliminating residual water responsible for EVOO oxidation and the onset of off‐flavors during its shelf life.

Many studies have been already developed during the last 10 years in order to optimize all the mechanical extraction steps that play a crucial role in the qualitative/quantitative composition of phenolic and volatile profile and, consequently, the sensory characteristics of the resulting EVOOs. Technological innovations have led to new extraction plants designed to improve the quality of oils obtained from olives with different genetic, geographical, and agronomic characteristics. More