Polyphenols in Olive Oil




An interview with Professor Dennis Fiorini on her latest research at the University of Camerino in Italy about a quantitative procedure employing high-performance liquid chromatography coupled with diode array detection to determine whether a given oil is entitled to a health claim. The research was conducted by Massimo Ricciutelli, Shara Marconi, Maria Chiara Boarelli, Giovanni Caprioli, Gianni Sagratini, Roberto Ballini and Professor Dennis Fiorini.


Let’s start off from the abstract of Professor Fiorini's most recent paper, Olive oil polyphenols: A quantitative method by high-performance liquid-chromatography-diode-array detection for their determination and the assessment of the related health claim.

In order to assess if an extra virgin olive oil (EVOO) can be acknowledged with the health claim related to olive oil polyphenols (EU Reg.  432/2012), a new method to quantify these species in EVOO, by means of liquid–liquid extraction followed by HPLC-DAD/MS/MS of the hydroalcoholic extract, has been developed and validated. Different extraction procedures, different types of reverse-phase analytical columns (Synergi Polar, Spherisorb ODS2 and Kinetex) and eluents have been tested. The chromatographic column Synergi Polar (250 × 4.6 mm, 4 μm), never used before in this kind of application, provided the best results, with water and methanol/isopropanol (9/1) as eluents. The method allows the quantification of the phenolic alcohols tyrosol and hydroxytyrosol, the phenolic acids vanillic, p-coumaric and ferulic acids, secoiridoids derivatives, lignans, pinoresinol and acetoxypinoresinol and the flavonoids luteolin and apigenin. This new method has been applied to 20 commercial EVOOs belonging to two different price range categories (3.78–5.80 euro/L and 9.5–25.80 euro/L) and 5 olive oils. The obtained results highlight that acetoxypinoresinol, ferulic acid, vanillic acid and the total non-secoiridoid phenolic substances resulted to be significantly higher in HEVOOs than in LEVOOs (P = 0.0026, 0.0217, 0.0092, 0.0003 respectively). For most of the samples analysed there is excellent agreement between the results obtained by applying the HPLC method adopted by the International Olive Council and the results obtained by applying the presented HPLC method. Results obtained by HPLC methods have been also compared with the ones obtained by the colorimetric Folin-Ciocalteu method.


Professor Fiorini, where did you get the idea for this line of research?
One of the main aims of the research project, framework of the investigation we are speaking about, was to find a way to highlight the virtues of select extra virgin olive oils. Polyphenols are fundamental for this purpose, and must always be taken in due account when assessing the quality of oil. These compounds give it greater stability, because they protect it from oxidation; they are also responsible for the pungency and bitterness of olive oil, and possess health properties that have been acknowledged by the EFSA, the European Food Safety Authority. As a consequence, the European Union has authorised a health claim stating that “Olive oil polyphenols contribute to the protection of blood lipids from oxidative stress” when the oil in question contains at least 5 mg of polyphenols, or better, hydroxityrosol and hydroxytyrosol and its derivatives (e.g. the oleuropein complex and tyrosol) per 20 g of olive oil. In other words, the threshold level is 250 mg polyphenols per kg of oil. The health claim must be accompanied with the additional information stating that the beneficial effect is obtained with a daily intake of 20 g of olive oil. It is worth mentioning however that, for a variety of reasons, it can be difficult to quantify these compounds. Oil polyphenols are a rather complex mixture of compounds that are hard to separate using the prevailing chromatography techniques and for which no commercial standards are available. Against this background, we felt the need to develop a new method whereby, by assessing various chromatographic conditions, it would be possible to better separate these compounds and by using an appropriate quantifying procedure, limit the range of error.


Is this an isolated investigation, or is your research group continuing to work in this sector? And if so, in what direction?
This investigation is part of a more extensive research programme called “AEVOO: Authentication of Extra Virgin Olive Oil” (FAR 2014/2015 grant, University of Camerino). This project has a number of goals, including the identification of new quality markers for oil, and of procedures aimed at highlighting the virtues of top-of-the-range oils made in our region (Marche) based on their chemical and biological characterisation. Another goal is the definition of simple, versatile and reliable analytical methods to analyse molecules of interest for the authentication and enhancement of the features of olive oil.


What is the practical use of this interesting investigation? What are its applications in analysis labs? Its potential use by technicians working in this sector? The benefits for consumers?
The analytical procedure described in this paper relies on instruments present in most laboratories. All you need is a high-performance liquid chromatographer equipped with a diode-array detector (HPLC-DAD) in order to establish whether an oil can bear the health claim mentioned previously, hence allowing its producer to highlight its benefits and virtues. Knowing exactly the content and composition of the phenols in a given oil can also help the producer create blends having appropriate levels of these its precious compounds. Lab technicians can use a relatively simple procedure, and instruments present in most laboratories, to perform analyses giving excellent results even from a quantitative point of view. Finally, the consumer gets more information on the health benefits of the oil, although it should be stressed that no class of molecules alone can ensure that the oil in question is of a superior quality. More

Photo of Professor Dennis Fiorini by Lorenzo Cerretani