## 1 Introduction
In addition, the preparation of the paste for the malaxation is initially made with the crushing of the olives, which is the first mechanical process of the fruits, and it has a fundamental role in starting all the biochemical processes [34; 35; 36]. However, the degree of innovation in this step is relatively lower compared with other stages in the production, mainly malaxation. A relevant early innovation was the use of a hammer crusher as an alternative to stone crushers, which was later coupled with a continuous centrifuge system [17]. The latter allowed a higher degree of automatization to permit a simple management of the process and enhanced quality [37]. Furthermore, the innovation in olive crushing continued with the invention of new cutting elements for the crushers, such as knife crushers and disk crushers. The purpose of this innovation was to perform a differentiated crushing that considers the location of the endogenous enzymes in the olive fruit [38]. This differentiated crushing resulted in an improvement in the quality, related to an increase in concentrations of volatile compounds and phenols. One of the latest innovations in crushing is the \"double effect crusher\", which is a mixed system between a disk crusher and a hammer crusher [39]. It maintains the principle of differentiated crushing explained above, but it can also produce a more homogeneous olive paste by using a sieve located externally to the disks [39]. The thermal conditioning during the crushing phase was also studied as an innovation to avoid the rise in temperature that normally happened due to the high quantity of kinetic energy given by the hammers to the olives that put up the temperature of the olive paste at 5 \({}^{\circ}\)C to 10 \({}^{\circ}\)C higher than the temperature of the olives before crushing [40]. Previous works implementing modification in production have demonstrated the importance of oxygen in the enzyme activities and in their effect on quality. However, the quantity of oxygen during the malaxation phase has been modulated [41]. In addition, when higher oxygen quantities were supplied, the concentration of volatile compounds increased, and, at the same time, it was observed that oxygen may oxidize phenolic compounds at different degrees according to malaxation temperature and cultivar differences. Other studies showed that the maximum activity of the lipoxygenase pool enzymes takes place in the initial part of the process while olive fruits are breaking up [4; 42; 43; 44]. Thus,these studies evidence that it is important to evaluate the effect of different parameters regulating the activities of the lipoxygenase pathway [45; 46]. There is a strong interest in understanding how the parameters of the technological process should be managed to obtain the desired results, as is typically the case in the food industry, in which all the production processes are strictly managed, especially in those cases in which biotechnological activities are involved [47]. Thus, from the point of view of EVOO production, the operating conditions should permit the best quality possible according to the specific enzymes' activities, which are dependent on the cultivars of the olive fruits [7; 22; 23; 48]. With this purpose, much research has addressed the study of the main factors that influence the activity of lipoxygenase enzymes, such as optimal working temperature, oxygen availability, type and concentration of fatty acids in the olive, and gene expression that modulates protein production [49; 50; 51; 52; 53]. Furthermore, given the importance of oxygen and the optimization possibilities of the crushing step, this work focused attention on testing a new configuration to control oxygen during olive crushing and to examine the effect of the different variables on the volatile and phenolic composition. With the purpose of evaluating the impact on oil quality when this configuration is implemented in a real production system, the study was carried out in an industrial pilot plant.