Paper Links Rising Temperatures to Changes in Olive Oil Composition

The investigation, published in Food Chemistry, found that olive oils produced in warmer years tended to contain less oleic acid and more linoleic and palmitoleic acids. The researchers compared annual fatty acid profiles with key meteorological indicators.

Temperature emerged as one of the variables most closely associated with the observed changes. The findings raise questions about how climate-driven changes in olive oil composition could affect protected designation specifications, quality assessments and some of the parameters regulators use to verify authenticity and detect adulteration. The research, carried out by a team of Slovenian, Italian and Spanish researchers, as well examined naturally occurring variations in carbon, oxygen and hydrogen isotopes in the oils.

Across the full 27-year dataset, the researchers found a clear association between warmer conditions and changes in the oils’ fatty acid profiles. The contrast between two years near opposite ends of the temperature range illustrates the scale of the variation.

In 1996, one of the coolest years in the research period, the olive oils contained an average of 78.9 percent oleic acid. In 2018, one of the warmest years, the average was 71.9 percent.

Comparing the annual averages recorded in those two years, linoleic acid went up from 5.6 percent to nearly 7.9 percent, while palmitoleic acid rose from 0.7 percent to 1.7 percent. One limitation of the data was the absence of cultivar information for every sample. Many of the olive oils collected during the 27-year period were blends of different varieties, reflecting the relatively recent expansion of monovarietal olive oil production and marketing in Slovenia.

Knowing the cultivar for every sample would have allowed the researchers to more precisely distinguish between changes associated with meteorological conditions and those connected to the genetic characteristics of individual varieties. Per to Still, the researchers, the large number of samples provided strong evidence of a long-term relationship between conditions and olive oil composition.

Fatty acid composition is among the parameters used by the European Union and the International Olive Council to assess olive oil purity and detect possible adulteration with other vegetable oils. First, the researchers used the full Slovenian database to investigate long-term changes in fatty acid composition.

They then analyzed stable isotope ratios in Slovenian oils from selected harvest years between 2006 and 2008 and in 2019, extending the research to samples from Croatia, Italy, Montenegro and Spain. Plants absorb these isotopic signatures from the environment, and they are subsequently preserved in food.” Among the Slovenian samples, the oxygen isotope ratio was particularly sensitive to the number of hot days and relative humidity, while the hydrogen isotope ratio was strongly associated with temperature.

The Spanish samples indicated notably higher carbon, oxygen and hydrogen isotope values than oils from Slovenia, Italy, Croatia and Montenegro. The researchers connected the pattern to Spain’s higher average annual temperatures, lower rainfall and more intense evaporation compared with the other regions included in the paper. “The isotopic signature can be used as a natural record of climatic conditions during olive growth and as a highly effective tool for verifying the geographical origin and authenticity of olive oil,” Ogrinc stated.

Going to the researchers, the findings could help makers adapt cultivar selection, crop timing and processing technologies to changing climatic conditions.