## 4 Discussion
Olive oils produced under deficit irrigation showed improved oxidative stability, as indicated by antioxidant capacity data, which is partly attributed to the higher concentration of phenolic compounds. These phenolics play a vital role in inhibiting the hydrolytic breakdown of triglycerides into free fatty acids,thereby protecting the oil from oxidation and helping to maintain low acidity levels [53]. In contrast, the presence of _Ailanthus_ led to increased ultraviolet absorbance indices. The competitive stress imposed by _Ailanthus_, an invasive weed [26; 27], may subject olive trees to various forms of physiological stress--such as water scarcity, nutrient imbalances, or potential toxicity--which can accelerate lipid oxidation and result in elevated extinction values in the extracted oil. Similar oxidative trends were reported by [PERSON] et al. [54] in oils from olive trees exposed to severe water deficit, reinforcing the connection between environmental stress and oil quality deterioration. Additionally, [PERSON] et al. [55] observed increases in both K232 and K270 values in olives grown under prolonged shading, which is a condition comparable to the canopy interference caused by fast-growing _Ailanthus_ stands. Likewise, [PERSON] et al. [56] demonstrated that potassium deficiency, a form of nutritional stress, can significantly raise K270 values. These findings support the idea that various abiotic stressors, including competition from invasive species, can negatively affect oil quality. The qualitative parameters of the olive oil analyzed in this study--including free acidity, peroxide value, K232, K270, and \(\Delta\)K--fall within the ranges reported in previous studies [57; 58; 59; 60]. Nonetheless, all oil quality parameters remained within the limits set by European Community regulations [31], confirming that all oils produced were of extra virgin quality. Deficit irrigation was found to significantly increase both the total polyphenol content and the antioxidant capacity of the olive oils produced in the present study. This result aligns with numerous previous studies that have reported a positive correlation between water stress and the accumulation of phenolic compounds in olive oil [39; 51; 61; 62]. The underlying physiological mechanism is believed to involve the activation of the enzyme phenylalanine ammonia-lyase (PAL), which plays a key role in the biosynthetic pathway of polyphenols. Water stress is known to enhance PAL activity, thereby promoting the accumulation of phenolic compounds in fruit tissues and, subsequently, in the resulting olive oil [63]. Furthermore, in the current study, deficit irrigation was associated with significant increases in both total ortho-diphenyl and total flavonoids, which are two major subclasses of polyphenols known for their potent antioxidant properties. These findings are consistent with earlier research [61; 64], which also demonstrated that deficit irrigation enhances the biosynthesis and accumulation of specific polyphen classes. The concentrations of total polyphenols measured in the present study fall within the range previously reported for the same olive cultivar in various regions of the country [59; 60], as well as in studies conducted in other countries [57]. Moreover, the findings are comparable to those documented for Mediterranean olive oils produced from other cultivars [65; 66; 67; 68]. The fatty acid profile, on the other hand, was not significantly affected by either the presence of _Ailanthus_ or deficit irrigation. However, [PERSON] et al. [69] and [PERSON] et al. [70] highlighted that limited irrigation can influence the fatty acid composition of olive oil. The ratio of monounsaturated to polyunsaturated fatty acids (MUFAs/PUFAs) appeared to remain unaffected by the irrigation regime, which aligns with the findings of [PERSON] et al. [21].