**3.3. Olive crushing**

The main hydrophilic phenols of VOO, such as secoiridoid aglycons, develop during crushing from the hydrolysis of oleuropein, demethyloleuropein and ligstroside, catalysed by the endogenous *β*-glucosidases (Servili et al., 2004a; Obied et al., 2008).The impact of crushing in the VOO phenolic and volatile compounds can be related to the differentiated distribution of the endogenous oxidoreductases and phenolic compounds in the constituent parts of the olive fruit (pulp, stone and seed). As reported in previous papers, the POD, in combination with the PPO, are the main endogenous oxidoreductases responsible for phenolic oxidation during processing. POD occurs in high amounts in the olive seed. The phenolic compounds, on the contrary, are largely concentrated in the pulp, whereas the stone and seed contain only small quantities of these substances (Servili et al., 2004a; 2007). As a result, the crushing methods, such as the olive stoning process or the use of mild seed crushers, which enable degradation of the seed tissues to be reduced by limiting the release of POD in the pastes, prevent the oxidation of hydrophilic phenols during malaxation, thus improving their concentration in the VOO (Figure 2) (Servili et al., 1999a, 2004a, 2007).

The operative conditions of crushing also affect the volatile composition of VOO (Table 1). As previously mentioned, almost all volatile compounds are responsible for the flavour of high quality VOOs when the olive pulp tissue is ruptured, thus the effectiveness of the crushing plays an important role in their production.

The traditional olive crusher used for many centuries was the stone crusher. The stone crusher consists of a basin formed by a plinth and a stainless steel edge with an opening for the unloading of olive paste at the end of milling. Two or four granite wheels rotate and revolve on a rough granite base at different distances from the centre of the tank. Rotation speed is normally 12- 15 rpm.

#### *Cv. Frantoio*

Technological Aspects of Olive Oil Production 157

*stoned* 

*crusher with a low number of rotations* 

degradation process of the olive tissues should be strong for the skin and pulp, in order to facilitate the release of oil and pigments, whereas impact on the seed should be limited. This reduces the transfer of POD found in the seed to the olive paste pulp, which can increase the oxidation of phenolic compounds during malaxation. The new generation of mild seed crushers, which include the blade crusher, teeth crusher and double stoker crusher, reduce the phenolic degradation and simultaneously improve the concentration of volatile compounds, especially of hexanal, trans-2-hexenal and C6 esters, with a consequent positive increase of the intensity of "cut grass" and "floral" sensory notes (Table 1) (Angerosa et al.,

*blade crusher* 

Pentanal 236.5 ± 4 273.4 ± 2.1 17.9 ± 1 66.5 ± 6.7 Hexanal 280 ± 2.9 511.4 ± 35.7 553.7 ± 0.3 579.6 ± 5.3 2-Hexenal (*E* ) 43600.6 ± 327 44718.9 ± 208 39811.6 ± 587 52228.1 ± 521

(*E,E*) 19.4 ± 0.1 42 ± 3.5 341.6 ± 14.4 88.9 ± 5.4

1-Pentanol 167 ± 5.2 94.5 ± 4.7 23.3 ± 0.7 62.6 ± 1.7 2-Penten-1-ol (*E*) 166 ± 11.3 91.4 ± 5.1 52.4 ± 3.5 104.0 ± 2.1 1-Penten-3-ol 960.3 ± 53.2 899 ± 43.3 522 ± 49.2 300.0 ± 4.6 1-Hexanol 1788 ± 57 2152 ± 74 512 ± 41 1501.0 ± 18.4 3-Hexen-1-ol (*Z*) 88.4 ± 22.2 103.6 ± 10.1 49.2 ± 2.3 77.0 ± 8.0 3-Hexen-1-ol (*E*) 22.2 ± 0.2 20.2 ± 0.1 9.9 ± 0.2 20.4 ± 2.3

**Table 1.** Effect of different crushing methods on the volatile composition of VOO in Cv. *Frantoio* (μg/Kg).Results are the mean value of three independent experiments ± standard deviation.

Several researches have shown that olive stoning during the mechanical extraction process of VOO increases the phenolic concentration in VOO (Figure 2) (Angerosa et al., 1999; Mulinacci et al., 2005; Lavelli & Bondesan, 2005; Amirante et al., 2006) and, at the same time, modifies the composition of volatile compounds produced by the LOX pathway, increasing the concentration of those volatile substances correlated to the "green" sensory notes (Table 1) (Servili et al., 2007). These results are particularly important, because they would appear to demonstrate that the enzymes involved in the LOX pathway have a different activity in the pulp and in the seed of the olive (Table 1)

The stoning process, moreover, produces a significant reduction in industrial oil yields. This problem is caused by stone elimination which, when present in the pastes, produces an important draining activity, which increases the efficiency of the separation of the oil from

*hammer crusher pre-crusher +* 

2004).

**Aldehydes** 

2,4-Hexadienal

(Servili et al., 2007).

the olive paste during solid-liquid extraction.

**Alcohols** 

**Figure 2.** Effect of different crushing methods on the phenolic composition of VOO in Cv. *Frantoio* (mg/kg). The vertical lines are the mean value of three independent experiments ± standard deviation.

The popularity of the stone crusher extraction system using pressure gradually declined. In comparison with continuous crushers, this apparatus shows significant limitations in terms of olive oil quality. In particular, it reduces the phenolic concentration as the olive pastes are in long, extensive contact with the air during processing. Contact with the air stimulates PPO and POD, producing a high oxidation of phenolic compounds. Other weaknesses of the stone crusher are its low working capacity, the high hourly machine footprint, and its low ability to release the chlorophyll found in the olive skin, responsible for the green colour of EVOO, into the oil. This aspect is particularly relevant when the stone crusher is combined with a solid-liquid centrifugal separation. The crushing operation in oil extraction by centrifugation is generally replaced by the use of continuous crushers.

Continuous crushers include the hammer crushers, which were historically the first to be introduced as an alternative to stone crushers. These machines have some benefits that are attributable to their high working capacity, low footprint, and low installation costs compared to the stone crushers. At the same time, the hammer crushers show some disadvantages, such as the strong emulsifier effect produced on olive paste during crushing, a considerable increase in paste temperature and the high degradation of the seed tissues which, as mentioned earlier, can encourage phenolic oxidation (Angerosa & Di Giacinto., 1995; Servili et al., 1999a; Servili & Esposto 2004).

The new approach to olive crushing is based on the differentiated crushing of the constituent parts of the fruit, such as the skin, pulp and seed. In other words, the degradation process of the olive tissues should be strong for the skin and pulp, in order to facilitate the release of oil and pigments, whereas impact on the seed should be limited. This reduces the transfer of POD found in the seed to the olive paste pulp, which can increase the oxidation of phenolic compounds during malaxation. The new generation of mild seed crushers, which include the blade crusher, teeth crusher and double stoker crusher, reduce the phenolic degradation and simultaneously improve the concentration of volatile compounds, especially of hexanal, trans-2-hexenal and C6 esters, with a consequent positive increase of the intensity of "cut grass" and "floral" sensory notes (Table 1) (Angerosa et al., 2004).

156 Olive Germplasm – The Olive Cultivation, Table Olive and Olive Oil Industry in Italy

**Figure 2.** Effect of different crushing methods on the phenolic composition of VOO in Cv. *Frantoio* (mg/kg). The vertical lines are the mean value of three independent experiments ± standard deviation.

hammer crusher pre-crusher + blade crusher crusher with a low number of

centrifugation is generally replaced by the use of continuous crushers.

1995; Servili et al., 1999a; Servili & Esposto 2004).

0

50

100

150

200

**mg/kg** 

250

300

350

400

The popularity of the stone crusher extraction system using pressure gradually declined. In comparison with continuous crushers, this apparatus shows significant limitations in terms of olive oil quality. In particular, it reduces the phenolic concentration as the olive pastes are in long, extensive contact with the air during processing. Contact with the air stimulates PPO and POD, producing a high oxidation of phenolic compounds. Other weaknesses of the stone crusher are its low working capacity, the high hourly machine footprint, and its low ability to release the chlorophyll found in the olive skin, responsible for the green colour of EVOO, into the oil. This aspect is particularly relevant when the stone crusher is combined with a solid-liquid centrifugal separation. The crushing operation in oil extraction by

rotations

stoned

*Cv. Frantoio*

Sum of the phenolic compounds Sum of the oleuropein derivatives Sum of the lignans Sum of the ligstroside derivatives

Continuous crushers include the hammer crushers, which were historically the first to be introduced as an alternative to stone crushers. These machines have some benefits that are attributable to their high working capacity, low footprint, and low installation costs compared to the stone crushers. At the same time, the hammer crushers show some disadvantages, such as the strong emulsifier effect produced on olive paste during crushing, a considerable increase in paste temperature and the high degradation of the seed tissues which, as mentioned earlier, can encourage phenolic oxidation (Angerosa & Di Giacinto.,

The new approach to olive crushing is based on the differentiated crushing of the constituent parts of the fruit, such as the skin, pulp and seed. In other words, the


**Table 1.** Effect of different crushing methods on the volatile composition of VOO in Cv. *Frantoio* (μg/Kg).Results are the mean value of three independent experiments ± standard deviation.

Several researches have shown that olive stoning during the mechanical extraction process of VOO increases the phenolic concentration in VOO (Figure 2) (Angerosa et al., 1999; Mulinacci et al., 2005; Lavelli & Bondesan, 2005; Amirante et al., 2006) and, at the same time, modifies the composition of volatile compounds produced by the LOX pathway, increasing the concentration of those volatile substances correlated to the "green" sensory notes (Table 1) (Servili et al., 2007). These results are particularly important, because they would appear to demonstrate that the enzymes involved in the LOX pathway have a different activity in the pulp and in the seed of the olive (Table 1) (Servili et al., 2007).

The stoning process, moreover, produces a significant reduction in industrial oil yields. This problem is caused by stone elimination which, when present in the pastes, produces an important draining activity, which increases the efficiency of the separation of the oil from the olive paste during solid-liquid extraction.

It should be noted that the use of enzymatic preparations with depolymerizing activities, degrading the colloidal structure of fruit might partly solve the problem of low yields due to the extraction of pastes for stoning. So far, however, the European Union (EU regulation) does not currently allow the addition of enzymatic preparations.

Technological Aspects of Olive Oil Production 159

These results are, in any case, obtained by performing malaxation with the pastes under continuous contact with air, as shown in the traditional mixer (Servili et al., 1998, 2003a).

However, when the process is performed in the new-generation malaxer, known as a "covered malaxer", which can control contact of the olive pastes with oxygen during mixing, the results obtained in terms of relationships between phenol concentrations in VOO and

During processing, the olive pastes release CO2 and the dissolved O2 is simultaneously consumed by the oxidoreductase activities. As a result, the reduction of the O2 content obtained in the covered malaxer inhibits the PPO and POD activities, improving the concentration of hydrophilic phenols in the olive pastes and in the corresponding VOO

Sum of the phenolic compounds Sum of the oleuropein derivatives

Sum of the ligstroside derivatives Sum of the lignans

**Figure 3.** Phenolic composition (mg/Kg) of VOOs obtained after malaxation in different initial

values of three independent experiments, standard deviation is reported in brackets.

0 kpa saturated with N2; 30 kpa corresponding to the air composition. The vertical lines are the mean

O2 0 Kpa O2 30 Kpa O2 50 Kpa O2 100 Kpa O2 0 Kpa O2 30 Kpa O2 50 Kpa O2 100 Kpa Cv. CORATINA Cv. OGLIAROLA

As a result, the oxidative reactions occurring in the pastes during malaxation can explain the relationships between VOO phenolic concentration and malaxation temperatures (Servili et al., 2004a; 2009a; 2009b). The O2 dissolved in the pastes during malaxation, activate POD and PPO, which oxidize phenolic compounds according to the temperature and consequently reduce their concentration in VOOs obtained by pastes malaxed at high temperatures. The traditional malaxer, which contains a high amount of O2 dissolved in the paste during the process due to contact with the air, represents a classical example of the aforementioned relationship between high temperatures and VOO phenolic loss. Low

the processing temperature are completely different.

(Figure 3) (Servili et al., 2008).

atmospheric compositions (Servili et al., 2008).

0

200

400

600

800

**mg/kg** 

1000

1200

1400
