The Chemical Analysis of Scripps’ 2013 Olive Oil

by Professor Anna Wenzel

Anna Wenzel

Out of the many domains of research expertise I have acquired in my scientific career, “olive oil exper” has been the most unexpected. However, this past spring, both Rachel Hamilton ’16 and I became just that. How did this happen?

In 2012, Scripps College conducted its first olive harvest and oil pressing, the final product of which was awarded an unprecedented “Best in Show” at the Los Angeles Extra Virgin Olive Oil Competition. Following this achievement, thanks to the efforts of many students, faculty, community members, and staff, led by Director of Grounds Lola Trafecanty, the 2013 pressing promised to be equally successful. However, a competition rules change posed a new challenge.

The new rules stated that olive oil entries would need to pass rigorous chemical testing to confirm the free fatty acid level and peroxide index of each submission conformed to the specifications required for classification as “extra virgin.” We learned of these new requirements less than a month before contest entries were due!

Hamilton and I soon joined the olive oil effort. Trafecanty asked me for assistance in performing a chemical analysis of Scripps’ olive oil. Thinking that olive oil couldn’t be too different from other oils I typically analyze with my medicinal chemistry students, I enthusiastically agreed, and Hamilton generously volunteered to assist.

The olive oil industry is big business: the U.S. alone spends $1.5 billion dollars a year on olive oil (Alban, 2014). As a result, counterfeit and adulterated olive oil products abound. To combat this, the International Olive Oil Council was founded to establish universal criteria for determining olive oil quality, such as acidity (the level of free fatty acid), oxidation (the level of peroxide), and color. According to the contest rules, to qualify as extra virgin olive oil (EVOO), the free fatty acid level present in the oil must be less than 0.8 percent. Fortunately, as a chemistry professor, my laboratory was well-equipped to allow Hamilton to quantify the precise measurements needed.

An excessive level of free fatty acid is indicative of poor olive quality and/or unsuitable harvesting, handling, transportation, and storage prior to pressing. Olive oil is composed mainly of triglycerides, which are composed of glycerol and fatty acids. Triglycerides serve as a major energy source for plants and animals — in other words, food. The breakdown of these triglycerides in the body primarily release oleic acid (up to 83 percent of the composition of olive oil), an Omega-9 fatty acid that has many healthful benefits, such as cancer prevention and cholesterol reduction (E. Waterman, 2007). However, if significant triglyceride breakdown occurs prior to consumption, this leads to a high level of free fatty acids in the oil.

The other criterion we measured was the peroxide index, which is a reflection of the presence of rancidity in the oil. Rancidity is an oxidative process primarily caused by the exposure of oils to oxygen in the air, heat, and/or light. This is why olive oil is generally sold in tightly capped, tinted bottles to protect it from prematurely becoming rancid. In the case of the contest specifications, a value higher than 20 milli-equivalent (milleq.) peroxide oxygen per kg/oil indicates the olives were either handled improperly or the resulting oil was defective.

Upon interviewing some of the harvesters, Hamilton and I quickly learned the Scripps olive harvest had occurred from 8 a.m. to 1:30 p.m. (a low-heat time of day), and that the olives had been delivered that afternoon to Ojai, California, for oil production. Pressing was performed within 24 hours of harvest, again another key factor in minimizing fruit damage and oxidation.

Once Hamilton and I received the olive oil sample, all testing was rapidly performed to keep exposure to air and damage to the oil to a minimum. In particular, the measurement of the peroxide content required Hamilton to perform the experimental setup under light-free and air-free conditions—an advanced-level technique, given that Hamilton was a sophomore who had only begun to work in my laboratory one week prior. All test results were successfully duplicated with high precision and rigorous quality control.

The team effort paid off. After final analysis, Hamilton and I were able to determine the free fatty acid content of Scripps’ olive oil was a mere 0.3 percent, and the peroxide value was only 1 milleq. peroxide oxygen per kg/oil.

According to our study, Scripps’ 2013 pressing of olive oil qualified as U.S. extra virgin by a large margin, thereby allowing the College to enter the competition with flying colors! The judges agreed: for the second year in a row, Scripps’ olive oil beat out 560 entries from 306 producers from countries such as France, Greece, Italy, and Spain, to win a silver medal in the “delicate” category.

The next time you have an opportunity to taste Scripps’ EVOO, I hope you will consider our educational adventure and be reminded of the remarkable things that can result from the collaboration of our amazing community of students, faculty, and staff.


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