From the 2011 UC Davis study:
Of the five top-selling imported "extra virgin" olive oil brands in the United States, 73 percent of the samples failed the IOC sensory standards for extra virgin olive oils analyzed by two IOC-accredited sensory panels. The failure rate ranged from a high of 94 percent to a low of 56 percent depending on the brand and the panel.
None of the Australian and California samples failed both sensory panels, while 11 percent of the top-selling premium Italian brand samples failed the two panels. Sensory defects are indicators that these samples are oxidized, of poor quality, and/or adulterated with cheaper refined oils.
- All of the oil samples passed the IOC chemistry standards for free fatty acids (FFA), fatty acid profile (FAP) and peroxide value (PV), but several of the imported samples failed the IOC’s ultraviolet absorption (UV) tests.
- 70 percent of the samples from the five top-selling imported brands failed the German/Australian 1,2-diacylglycerol content (DAGs) test and 50 percent failed the German/Australian pyropheophytin (PPP) test. All of the 18 samples of the California brand passed the DAGs test and 89 percent of the samples passed the PPP test. The Italian premium brand failed the DAGs and PPP tests in about one-third of the samples. The Australian brand passed the DAGs test in all cases and failed the PPP test in all cases.
- The strongest relationship between chemical analysis and negative sensory results was found in the DAGs test (65 percent), followed by the PPP test (49 percent), UV K268 for conjugated trienes (34 percent), UV K232 for conjugated dienes (12 percent) and UV ?K (6 percent). The FFA, FAP and PV tests did not confirm negative sensory results. The IOC standards would be more effective in assessing and enforcing olive oil quality by including the DAGs and PPP standards.
Our testing indicated that the samples failed extra virgin olive oil standards according to one or more of the following: (a) oxidation by exposure to elevated temperatures, light, and/or aging; (b) adulteration with cheaper refined olive oil; and (c) poor quality oil made from damaged and overripe olives, processing flaws, and/or improper oil storage.
Find the original report here: http://olivecenter.ucdavis.edu/research/files/report041211finalreduced.pdf