DAVIS, Calif.—That extra-virgin olive oil on the store shelf may not be what it claims to be. A study from the UC Davis Olive Oil Chemistry Laboratory found two-thirds of the extra-virgin oil found in California grocery stores did not meet international and U.S. standards. Some were tainted with lower-quality oils; others had defective flavors such as rancid, fusty and musty.
In fact, negative sensory results were confirmed by chemical data in 86 percent of the oils. Chemical testing also revealed oils failed the “extra virgin” standards because they were oxidized by exposure to elevated temperatures, light, and/or aging; adulterated with cheaper refined olive oil; or made with poor-quality oil from damaged and overripe olives; were processed incorrectly; and/or were stored improperly.
Laboratory tests indicated the imported oil was more likely to fail the tests, with 69 percent of imported olive oil samples and 10 percent of California olive oil samples labeled as extra-virgin olive oil failed to meet the sensory standards for extra-virgin olive oil.
One-third (31 percent) of the imported samples that failed the sensory standards also failed the standards for UV absorbance of oxidation products, which indicates these samples were oxidized and/or were of poor quality.
Along with the Australian Oils Research Laboratory, California researchers collected 14 imported brands and five California brands of extra virgin olive oils from three different regions of California (County of Sacramento, San Francisco Bay Area, and County of Los Angeles) from March 3, 2010 to March 10, 2010. The oils were purchased at Whole Foods Market, Ralphs and Wal-Mart. The two laboratories evaluated the oils based on standards and testing methods established by the International Olive Council (IOC) and United States Department of Agriculture (USDA), as well as several newer standards and testing methods adopted in Germany and Australia. These latter tests were adopted to help detect the adulteration of extra virgin olive oils with refined olive oils.
Researchers found the IOC and USDA chemistry standards often do not detect defective olive oils that fail extra virgin sensory standards, and they recommended The IOC/USDA standards to included the German/Australian 1,2-diacylglycerol (DAGs) and pyropheophytins (PPP) standards. They noted elevated level of DAGs indicates oils are oxidized, of poor quality, and/or adulterated with cheaper refined oils, while an elevated level of PPP indicates the samples are oxidized and/or adulterated with cheaper refined oils.