Influence of growing season temperatures in the fatty acids (FAs) of triacilglycerols (TAGs) composition in Italian cultivars of Olea europaea

In an olive genebank near the Ionian Sea in Calabria (southern Italy) a comparative study on the TAGs composition of 188 Italian cultivars was carried out from 2001 to 2005. To be considered in the study, data for the cultivar had to be present from at least two of the five study years. Samples (around 15 kg) of fruits at ripening stage were harvested to produce the investigated oils by utilising a laboratory oil mill, which were then analysed according to the official analysis methods, Reg. C.E.E. 2568/91 and E.U. modifications. Extreme variability characterized the percentages of each FA, making each cultivar "peculiar" in its TAG composition. In the same year (e.g. 2003), the percentage of oleic acid increased from a minimum of 49.8% (cv. Orbetana) to 78.2% (cv. Simona) and the percentage of linoleic acid ranged from 3.9% (cv. Simona) to 23.9% (cv. Racioppella), a variation of more than 500%. The year effect is evident, despite the large number of samples in each year: oleic acid varied from 67.5% in 2003 to 73.4% in 2005 and important differences can also be noted for palmitic and linoleic acid averages. Temperature from stone hardening until the beginning of turning colour is probably the primary contributing factor with regard to these variations. A linear regression between the thermal sums accumulated in this period and the levels of oleic acid shows a decrease in the percentage of this FA with an increase in the GDD. The ternary plot system presents a different distribution of the data from the 69 cultivars in 2003 (warmest year) and 2005 (coolest year) relative to three groups of FAs (SFAs, MFAs and PFAs). The lowering of the percentage of MFA groups and the prevalent tendency to increase the SFAs is evident, with important movement also in the zone of increasing PFA group. Grouping the possible tendencies of different cultivars is evaluated by a "fuzzy" clustering analysis, dividing the population into three "groups": in two of them the MFA amounts decrease, substituted mainly by SFAs (the first and most conspicuous cluster) or by PFAs (second cluster); an inconspicuous but notable cluster constituted by three cultivars only, characterized by a practically constant level of MFAs, with the effect of the warm year on lowering PFAs, is also highlighted.