## 3 Results and Discussion
### Chemical and Physical-Chemical Parameters
#### 3.1.1 Effect of the Organic Production (Organic vs. Conventional)  
In the case of the type of production system (Organic vs. Conventional), the effect was significant on the peroxide value (PV), the total phenols and the oxidative stability of oils (Table 1). The values averaged over the six week period for the Organic and Conventional oils are shown in Figure 1. Compared with the Conventional group, the Organic one had lower values for PV (\(9.63\pm 1.93\) vs. \(11.26\pm 2.12\) mEq O\({}_{2}\) kg\({}^{-1}\)), and higher for the total phenols (\(166.7\pm 15.0\) vs. \(149.0\pm 12.2\) mg kg\({}^{-1}\)) and the oxidative stability (\(26.3\pm 2.1\) vs. \(22.9\pm 2.0\) h). However, most quality parameters (free acidity and the extinction coefficients) were not affected (\(p>0.730\) for all of them) (Table 1). \begin{table}
\begin{tabular}{c c c c} \hline  & **Type of Production** & **Harvesting Method** & **Harvesting Time** \\ \hline Free acidity (\%) & 0.953 & \(<\)0.001 & 0.388 \\ PV (mEq O\({}_{2}\) kg\({}^{-1}\)) & 0.026 & \(<\)0.001 & 0.006 \\ \(K_{232}\) & 0.965 & 0.016 & 0.488 \\ \(K_{270}\) & 0.823 & 0.024 & 0.506 \\ \(\Delta K\) & 0.738 & \(<\)0.001 & 0.276 \\ Total phenols (mg kg\({-1}\)) & 0.039 & \(<\)0.001 & 0.650 \\ Oxidative stability (h) & 0.006 & \(<\)0.001 & 0.146 \\ \hline \end{tabular}
\end{table} 
Table 1: \(p\)-Values from a three-way ANOVA (type of production, harvesting method and harvesting time) performed on the chemical and physical-chemical data of Verdial de Badajoz olive oil. Figure 1: Mean values and standard deviation for the chemical and physical-chemical parameters over the six week period for the Organic (\(\blacksquare\) ), Conventional (\(\blacksquare\) ) and Ground (\(\blacksquare\) ) oils. Different letters indicate statistical differences (Tukey test’s \(p<0.05\))The lack of a marked effect on most of the quality parameters might be expected as the agronomic practices were very similar (no irrigation in both cases, and little vs. no use of phytosanitary chemicals) except for fertilisation. Currently, there is no general agreement on what the effect of the organic practices on the virgin olive oil quality is, apparently because of the difficulty of dealing with a relatively weak effect without excluding other environmental sources of variation. In this sense, a three-year study on the Leccino and Frantoio olive cultivars showed non-consistent differences in the oil quality parameters and phenol content due to the organic practices, suggesting that genotype and year-to-year variations in climate have a stronger effect [9]. However, both a decrease and an increase in oil quality have been reported in other studies. On the one hand, a decrease in oil quality (free acidity and \(K_{270}\)) was reported and attributed to infestation and fungal infection in the organic fruits as a consequence of the absence of pesticides [21]. Likewise, lower phenol contents have been reported in organic Picaual and Hojiblanca oils than in the conventional ones [13]. On the other hand, an increase in oil quality or/and in phenol content was also reported as a result of the organic practices. A study on Picaul oil showed lower values for PV, greater stability and higher phenol content in the organic oil than in the conventional one [22], which is in line with our results for Verdial de Badajoz oil. More recent research on Leccio and Frantoio olive oils found no effect on the quality parameters but showed an increase in the phenol content, which was attributed to the decreased availability of soil nitrogen when using organic practices, as phenol content increases with decreased soil nitrogen availability [23], suggesting that, under controlled environmental conditions, the effect of the agronomic practices on plant metabolism is clear [8]. Similarly, organic practices on Kolovi olive orchards resulted in an increase in phenols, including luteolin, which was proposed as a marker for organic production [24].