The effect of irrigation and harvest time on bioactive properties of olive fruits issued from some olive varieties grown in Mediterranean region

In this study, the effect of irrigation, variety (Ayvalık, Çöpaşı, Gemlik and Yağlık) and harvest time from August to December in both 2017 and 2018 on total phenolic content, DPPH and ABTS free-radical scavenging activities and phenolic compounds by HPLC of olive fruit was investigated. Limited study on the combined effects of the irrigation and harvest time in olive varieties with commercial value in Turkey was conducted. The current study is important for detecting the differences in bioactive properties of irrigated and rain-fed olives based on harvest time. The highest total phenolic content (8457.80 mg/kg) and antioxidant activity values (8.63 mmol TE/100 g) were obtained in the Yağlık olive, followed by the Çöpaşı variety. The verbascoside (1088.40–2634.20 mg/kg) was found as the major phenolic compound in all olive varieties for this location. In both harvest years, hydroxytyrosol (307.30–1449.10 mg/kg) and oleuropein (577.40–1404.80 mg/kg) contents of the Yağlık variety were higher than other varieties. Total phenolic contents and antioxidant activities of olives (especially Ayvalık and Gemlik varieties) decreased by irrigation. According to the results, Yağlık olive was the most outstanding one in terms of bioactive components. Irrigation time and amount should be determined separately for each variety. Additionally, irrigation would not be recommended for Ayvalık and Gemlik varieties in this location because it caused a significant decrease in the bioactive properties.