## 4 Discussion
### Effect of Si Foliar Application on Olive Oil Polyphenols  
The effect of phenolic compounds in olive oil has been investigated, and it was shown to have a decisive positive influence on the oxidative stability of olive oils, and that they determine the bitterness and pungency as distinctive sensory characteristics of olive oils [68; 69]. Si foliar fertilization has increased levels of oleupropin, apigenin-7-O-glucose, luteolin-4-O-glucose, rutin, and tyrosol in olive leaves [36]. Effects of foliar fertilization on the polyphenolic contents of olive oil has been researched much less commonly than its effect on leaf polyphenols. [PERSON] et al. [27] showed that foliar application of kaolinite and chabazite (CHA)-zeolithic can modulate the contents of some polyphenols in olive oil; increased contents of apigenin and pinoresinol and decreased content of vanillic acid. Foliar application of silicon nanoparticles on summer savory showed that it can modify the contents of major polyphenolic components in oil [70]. Our investigation showed that none of the investigated polyphenols were affected singularly by the applied Si treatments, and only a few were affected by the two-way interaction of Si application and cultivar. These were tyrosol, apigenin, phenolic acids and flavonoids. Contrary to the application of CHA-zeolitite and kaolinite by [PERSON] et al. [27], apigenin content decreased with Si3 treatment for the L cultivar, and for the IB cultivar with Si2 treatment. Significantly higher values of hydroxytyrosol acetate in the L cultivar could potentially provide a beneficial effect against murine collagen-induced arthritis [71]. Cultivar can have a very large influence on the polyphenolic content of olive oil (reviewed by [PERSON] et al. [69]), which was evident in our research, as only a few polyphenolic compounds were affected by treatment, and almost all were affected by cultivar. In the research of [PERSON] et al. [61], oil produced from the IB cultivar had a significantly higher content of total phenols compared to the L cultivar. [PERSON] et al. [72] reported that IB cultivar extra virgin olive oil showed higher contents of hydrophilic phenols compared to L cultivar during two years of research. This was also confirmed by [PERSON] et al. [73] in a two-year experiment, where the IB cultivar had significantly higher total polyphenic content compared to the L cultivar. This is in concordance with our results, as total phenols were also higher in the IB cultivar, as well as antioxidant activity and several of the most abundant polyphenols, such as oleupopein and its aglycone, hydroxytyrosol, luteolin and apigenin. Effect of Si Foliar Application on Fatty Acid Composition and Physico-Chemical Quality Parameters of Olive Oil  
The fatty acid composition has been shown by previous research to be highly dependent on olive cultivar and crop year. Cultivar especially influences the oleic to linoleic acid ratio and triglyceride content [69]. Generally, the cultivar effect dominates over the crop year effect, especially in some Portuguese cultivars (e.g., Redondal and Verdeal Transmontana) that have shown consistently and homogenously high contents of MUFA [21]. Authors have also shown that cultivar highly influences the relative content of both oleic and palmitic acids, i.e., cultivar effects on fatty acid composition were sufficiently large that, by using linear discriminant analysis, cultivar could be correctly classified with 92% sensitivity based on nine fatty acids. Similar results were obtained by [PERSON] et al. [8], as they were able to classify 199 virgin olive oil samples from four olive cultivars with 99% accuracy. Their chemometric analysis used 11 fatty acids and several parameters calculated from their contents.