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New TASC Report Identifies Unique Chemical Profiles of US Olive Oils

By Lori Zanteson

A new study identifies chemical and sensory profiles unique to American produced olive oils in order to better evaluate and modify the current US Standards for Olive Oil and Olive-Pomace Oil. The research project was conducted by the UC Davis Olive Center under the direction of the California Olive Oil Council (COOC) as a part of their continuing efforts to improve the quality of olive oils produced in the US.

This second study funded by the USDA’s Technical Assistance for Specialty Crops (TASC) grant program, builds upon the 2009 findings which produced important data on US olive oils that failed certain chemical limits of the standards set by the International Olive Council (IOC) for an oil to be classified as extra virgin. Most notably, the study found that a large percentage of oils containing the Arbequina variety of olive, the largest planted variety in the US, had higher levels of campesterol than the IOC standard permits.

Data from the TASC reports call into question the relevance of the IOC standards for US-produced oils due to the differences in the relationship of chemical profiles to cultivar and geographic location and climate. The IOC standards are based on chemical data from olives grown in countries representative of the majority of olive oil producing regions of the Mediterranean, which may not be appropriate for US oils and could create potential trade barriers.

Designed and led by Dr. Selina Wang PhD, Research Director of the UC Davis Olive Center, the study analyzed sixty mono-varietal extra virgin olive oils produced in the US from the 2010 harvest. Data was gathered using chemical and sensory testing standards from the USDA standards for olive oil grades as well as two more chemical tests first used in Germany and Australia, diacylglycerol (DAG) and pyropheophytin (PPP), meant to indicate olive oil age and freshness. Tests were conducted independently by three laboratories (USDA Blakely laboratory, Australian Oil Research Laboratory (AORL), and UC Davis Olive Center) and three sensory panels (Australian Oil Research Laboratory (AORL), UC Davis Olive Center, and California Olive Oil Council).

As suggested in the findings from the TASC 2009 Report, several of the oils tested fell above the IOC campesterol limit, but only one exceeded the USDA limit, indicating that the USDA standard is more suitable for US extra virgin oils. Interestingly, the one sample that exceeded the US limit was a Koroneiki cultivar, whereas three other Koroneiki samples had less overall sterols than the limit, which may suggest a correlation worthy of future examination.

Similar investigation was determined for the fatty acid profile. Because they are well known to be influenced by olive cultivar, geographical location, and climate, USDA standards allow higher levels of linolenic acid than the IOC standard and the samples reflected the appropriate levels. However, nine of the samples exceeded the USDA limit for heptadecenoic acid, indicating a correlation between several specific cultivars that may result in the recommendation to increase the limit of heptadecenoic acid in the USDA standard.

As well as indicating the need to increase certain limits to make them more suitable for domestic olive oils, results of some chemical tests, such as peroxide value and free fatty acids have an upper limit that may be too high, allowing poor quality oils to slip into the standards. While none of the samples failed Australia’s DAGs and PPP tests, the fact that ten samples failed the sensory test indicates a need to evaluate and possibly adjust limits for these tests if they are to be adopted into the US standards.

Future studies are planned, according to Dr. Wang. One in particular, which is similar to a project done in Australia, will begin with the olives. By collecting olives directly from growers and extracting the oil and testing it in the lab, explains Wang, “we will be able to have more control of the oil sample and make sure the chemistry profile isn’t affected by the processing and storage from different producers.”

Updating standards to accommodate the natural chemistry of US-produced olive oils is necessary to ensure a healthy US olive oil industry. But, as the report concludes, the current 2010 US Standards for Olive Oil and Olive-Pomace Oil covers quality through chemical and sensory testing, but it doesn’t measure freshness. The optional “best by” date on some labels has proven elusive at best and is therefore useless to buyers. Further research to determine the “life” of olive oil will help buyers choose both quality and freshness.

Read the TASC 2011 Project Report.

Errata 3/22/2012: As originally published, we erred in certain information about campesterol limits. This error has since been corrected in the text above.