Polyphenolic compounds, antioxidant activity and l-phenylalanine ammonia-lyase activity during ripening of olive cv. "Cobrançosa" under different irrigation regimes

Changes in the polyphenol composition and content, l-phenylalanine ammonia-lyase and antioxidant activity in different water treatments applied (rainfed (T0), deficit irrigation (T1) and applying a dose of irrigation equivalent to 30% of evapotranspiration (ET) and well watered (T2)) to the Portuguese olive tree cultivar Cobrançosa were studied during olive fruit ripening. The polyphenol content, PAL and antioxidant activity decreased during fruit maturation and were significantly affected by the water treatment applied (PAL - 120.0 to 35.8μmol cinnamic acidh-1g-1 for T0, 52.5 to 28.3μmol cinnamic acidh-1g-1 for T1 and 45.5 to 23.4μmol cinnamic acid h-1g-1 for T2; polyphenol content - 61.3 to 15.7mgGAEg-1 for T0, 24.5 to 11.2mgGAEg-1 for T1 and 14.7 to 10.2mgGAEg-1 for T2; antioxidant activity - 236.6 to 43.2mmolTrolox/kg for T0, 98.8 to 27.3mmolTrolox/kg for T1 and 60.3to 27.8mmol Trolox/kg for T2).The content of the individual phenolic compounds including phenolic alcohols, phenylpropanoids, flavonoids and secoiridoids decreased during maturation and were affected by the irrigation treatment, being lower with the increase in the water applied during irrigation, although the difference decreases as olive became more mature. This decrease in polyphenols was highly correlated with the decrease in PAL activity of olive fruits. The rainfed conditions applied to the olive trees during fruit maturation yield olive fruits with higher total polyphenol and PAL activity, so the irrigation can have a negative impact on the olive oil quality obtained from Cobrançosa cv. due to a decrease in the amount of total polyphenols of the olive fruits.