# Filtration Scheduling: Quality Changes in Freshly Produced Virgin Olive Oil
## 3 Results and Discussion
### Volatile Compound Contents
#### 3.3.1 Pleasant LOX Pathway Volatile Compound Contents  
Experimental data has identified several statistically significant differences (\(p\)-value \(<\) 0.05) in the LOX pathway [7; 8; 12; 40; 41; 42; 43] related to the filtration treatment, storage time, and their interactions.  
Figures 2 and 3 show the kinetics of LOX volatile compounds from the C6 and C5 branches, respectively. In all samples, there is a statistically significant decrease in the LOX volatile compound contents as a result of filtration; the ANOVA highlighted a significant (\(p\)-value \(<\) 0.05) main effect of filtration. On average, 27.3% of the LOX compounds were removed by filtration, but this varied as a function of the chemical properties of specific compounds. The smallest decrease was found for Z3-hexen-1 ol (\(-\)8.5%), compared to \(-\)53.1% for hexanal. These observations are consistent with data reported in the literature [44] and could explain the less fruity perception of the filtered samples compared to the veiled samples measured by the panel test at the beginning of storage.  
Figure 2: Mean contents of the lipoxygenase (LOX) compounds for the C6 branch in veiled (blue squares) and filtered (red circles) olive oil samples during storage.  
A statistically significant interaction between filtration and storage time (\(p\)-value \(<\) 0.05) was found for the following LOX volatile compounds: 1-hexanol, E2-hexen-1-ol, Z3-hexen-1-ol, Z3-hexenyl acetate, and 1-penten-3-ol. All showed the same behaviour. After a specific storage time, the organic compound content in the veiled oil samples started to increase, while it remained constant in the filtered samples. For example, the 1-hexanol content remained at 0.4-0.5 mg/kg until the fifth day of storage in both the filtered and veiled samples. However, at 30 days, it reached 1.7 mg/kg in veiled oils compared to 0.4 mg/kg in filtered oils. Similarly, the E2-hexen-1-ol content was below the detection threshold until the third day of storage in all samples but reached a mean of 25 mg/kg at the end of storage for the veiled oils. This behaviour could be related to the enzymes that are responsible for the LOX pathway. They remain active in veiled samples thanks to the residual water content and high water activity; however, they are inhibited in filtered samples due to the almost complete absence of water and low water activity.  
Some authors have claimed that the increase in LOX compounds in veiled oil samples is responsible for an increase in the pleasant fruity attribute; on the other hand, other research has found that several of the compounds that increased in veiled oils, which are considered as positive at low concentrations, have an unpleasant odour at higher concentrations. Specifically, 1-hexanol has been perceived as \"rough mouthfeel and rancid\"; E2-hexen-1-ol as \"wine-like, undesirable\"; Z-3-hexen-1-ol, Z-3-hexenyl acetate, and 1-penten-3-ol as \"wet earth, undesirable\"; and 1-penten-3-one as \"unpleasant\" [12; 40; 41; 43].  
We were unable to establish whether the observed changes in the volatile compound contents represented an improvement or a deterioration in the odour of veiled oil, as our panel test did not perceive any of the above defects. Nor did it reveal any significant increase in the fruity attribute as the storage time increased. It is possible that the formation of the frusty defect (see next paragraph) masked the increase in the fruity attribute to the point that the filtered samples appeared fruitier than the veiled samples.