## 3 Results  
### Effect of PEF Technology on Oil Yield  
As previously mentioned in the introduction, increasing malaxation time and temperature up to a certain degree increases oil extraction yield but negatively affects oil quality. In this sense, new extraction technologies focus on reducing malaxation time and temperature without reducing the oil yield [12]. Thus, in the first pilot trials, the effect of applying a PEF treatment in combination with a reduced malaxation stage (45 min) was compared to the standard industrial protocol with longer malaxation times, 90 min. for 'Manzanilla' fruits at turning stage (Table 1). Under these conditions, the standard process (control) gave rise to an oil yield 1% higher than the PEF process, using any of the methods to evaluate the efficiency of the extraction, mass balance or quantification of the remaining oil content in the olive pomaces (Table 2). However, when a short malaxation time was fixed (30 min) to compare exclusively the effect of PEF technology on the oil extraction process, it was observed that in general a higher oil yield was obtained in the pilot extractions conducted with PEF technology on both cultivars 'Manzanilla' and 'Hojiblanca' (Table 2). The best results in terms of oil yield were obtained in the industrial trials conducted with 'Manzanilla' fruits, in which the oil content of the olive pomace obtained was reduced by about 23% (from 16.6 to 12.7%) by applying PEF technology compared to the controlprocess. Previous studies had already highlighted the potential of the PEF to increase the oil yield. However, in many of these studies oil extractions were conducted with a lab scale. Thus, increases of up to 1.7% oil yield have been described from 'Arbequina' fruits in tests conducted with a lab scale [19]. Working on a similar scale (close to 1 kg of olive fruits extraction), oil yield increases of around 1% have also been described for the Greek olive cultivars 'Anfisis' and 'Manaki' although the application of PEF technology had no effect on the olive cultivar 'Isounati' [16]. At semi-pilot and pilot scales, positive results have been obtained with some Italian cultivars such as 'Carolea', 'Coratina' and 'Nocellara del Belice' [18; 28] though negative results were obtained with cultivar 'Ottobratica' in similar conditions. These results and those that we have found in terms of oil yield with the cultivars 'Hojiblanca' and 'Manzanilla' suggest that it seems reasonable that the use of PEF technology must be specifically adjusted to the different characteristics of the olive fruits that arrive at the olive oil extraction plant.  
Processing temperature seems also to be a critical point according to differences observed in terms of oil yield in the extraction trials conducted with 'Manzanilla' fruits. Thus, the oil extraction yield is inversely proportional to the malaxation temperature used, showing higher yields when the extraction was conducted below 20 \({}^{\circ}\)C (Tables 1 and 2). Similarly, [PERSON] et al. [19] reported significant increases in oil yields in samples treated with PEF technology and extracted at 15 \({}^{\circ}\)C, but not when the experiments were conducted at 25 \({}^{\circ}\)C. More recently, [PERSON] et al. [17] also concluded that the best results in terms of oil yield and quality were obtained when low malaxation temperatures were used in the combined application of PEF technology and high pressure on a lab scale. In relation to malaxation temperature, it is important to point out that only minor, non-significant increases of the temperature were detected in PEF-treated olive pastes (Table 1).