EFFECT OF IRRIGATION AND PRUNING ON THE AMOUNT OF SUBSTANCES RELATED TO THE OXIDATIVE STABILITY OF VIRGIN OLIVE OIL OF THE CULTIVAR 'FARGA' (MENDOZA, ARGENTINA)

The effect of different irrigation and pruning strategies on the amount of substances related to the oxidative stability of virgin olive oils of the cultivar ‘Farga’ (polyphenols, chlorophylls, carotenoids and fatty acids), were analyzed. Four treatments were used: T100%SP (irrigation supplying 100% of the plants’ evapora-tive transpiration demand (Etc) during the entire cycle, without winter pruning); T50%SP (irrigation supplying 50% of the plants’ Etc from pit hardening to harvest, without winter pruning); T100%CP (irrigation supplying 100%, with pruning) and T50%CP (irrigation supplying 50%, with pruning). Irrigation was applied “at real time” replenishing estimated daily intakes. The plants’ hydric status was monitored through the midday stem water potential (SWP), the soil moisture content and the photosynthetically active incident radiation within the tree branches. Fruit were sampled, sampling was made from pre-ripening to full maturity. Fruit maturity index, moisture content and oil concentration were determined at each sampling time. Also chlorophylls, carotenoids and total polyphenols, were determined by spectrophotometry on oil mechanically extracted. Fatty acids composition was determined by capillary gas chromatography (CGC).
The T50% treatments received 75% of the total amount of water received by the control treatment (T100%), which represents a 25% saving of irrigation water throughout the crop cycle. Oil concentration showed no statistical differences between deficit irrigation covering 50% of the ETc and the control treatment, both in plants with or without pruning. The content of polyphenols, chlorophylls and carotenoids in oils decreased with fruit ripening, regardless of the initial content and treatment. Deficit irrigation treatments (T50%) had higher contents of polyphenols, chlorophylls and carotenoids in oils. There were no statistically significant differences between treatments with and without pruning. In conclusion, the controlled deficit irrigation increased the content of polyphenols, chlorophylls and carotenoids in virgin olive oil of ‘Farga’ regardless of the applied pruning treatment.