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The quality of extra-virgin olive oils (EVOO) from organic and conventional farming was investigated in this 3-year (2001-2003) study. The oils were extracted from Leccino and Frantoio olive (Olea europaea) cultivars, grown in the same geographical area under either organic or conventional methods. Extra-virgin olive oils (EVOO) were produced with the same technology and samples were analyzed for nutritional and quality parameters. Volatile compounds were measured with solid-phase microextraction combined with gas chromatography and mass spectrometry (SPME-GC-MS). Sensory evaluation was also completed by a trained panel. Significant differences were found in these parameters between organic and conventional oils in some years, but no consistent trends across the 3 years were found. The acidity of organic Leccino oils was higher than conventional oils in 2001 and 2002 but not in 2003; Frantoio oils were never different. Organic Leccino oils had higher peroxide index than conventional oils in 2001 and 2002 but it was the reverse in 2003. Organic Frantoio oils had lower peroxide index in 2001, but values were not statistically different in the other years. The concentrations of phenols, o-diphenols, tocopherols, the antioxidant capacity and the volatile compounds showed differences in some years and no difference, or opposite differences, in others. Sensory analysis showed only slight differences in few aromatic notes. Our results showed that organic versus conventional cultivation did not affect consistently the quality of the high quality EVOO considered in this study, at least in the measured parameters. Genotype and year-to-year changes in climate, instead, had more marked effects.

In the study of Gutierrez et al. [16], the pest control was obtained with several pesticides, including malathion, formothion, glyphosate, oxyfluorfen, Bordeaux mixture and simazine as herbicide, while in our study pests were controlled using dimethoate only. It is possible that the use of many chemicals might have affected the quality parameters, but it is difficult to ascertain this hypothesis.

Finally, Gutierrez et al. [16] focused their study on the differences between conventional and organic oils following the ripening index of the fruits from 3.5 to 5. Although some significant differences between organic and conventional oils were present in the oils extracted at the ripening index of 3.5, the difference increased with the maturation index. We harvested most of our olives at a lower ripening index (i.e. between 2.5 and 3.5), because this is considered the best value for maximum oil quality [22, 24]. It may be possible that with less ripe fruits or with higher quality oils we were unable to find clear and consistent differences among treatments, which can emerge with more ripe olives and lower quality oils.

With two cultivars and 3 years of experimentation, our study provided a broad experimental base where the differences found in one year were not confirmed in other years.

Our findings agree with the majority of previous works [7, 8] where differences in nutrient content and sensory properties between organic and conventional foods were not found or were inconsistent over time. This is probably because the nutrient and sensory qualities of foods depends on a variety of factors, including cultivar, climate, soil type, nutrient and water availability, duration and conditions of storage [9,10, 30,31] and the differences related to the cultivation methods may be difficult to observe.