Evaluating the Quality of Extra Virgin Olive Oil

BENDINI (University of Bologna):

Have you ever found yourself looking to buy a bottle of vegetable oil at the supermarket only to find yourself staring at the display of many different products without being able to choose one? If you look long enough, you may find yourself going from seed oil to pomace olive oil, to olive oil, and in the end, to extra virgin olive oil. Consumers from the Mediterranean area, based on their cultural heritage and traditions, may choose to buy a type of oil derived from olives. Similarly, well-informed consumers may choose virgin olive oil for its nutritional, health and sensory properties.

European regulations have different requirements for the process of extracting extra virgin olive oil as compared to other vegetable oils. Extra virgin olive oil must be obtained from the mechanical crushing of olives and should not be subjected to chemical or physical treatments that change its composition. In addition, it must be not objectionable in terms of chemical and sensory parameters and must be edible as is. To maintain the high quality of extra virgin olive oil, production costs must be higher than for other vegetable oils.

But how is it possible that some extra virgin olive oils are sold at a comparable or lower prices than olive oil, pomace olive oil, or seed oils? The answer has to do with marketing strategies; for example, wholesalers can employ a bait-and-switch pricing strategy for extra virgin olive oil to attract consumers to the point of sale. As often happens with premium quality foods, the extra virgin olive oil may be subjected to adulteration — for example, with illegal blends of low-quality vegetable oils.

The research group of Instrumental and Sensory Analysis (Food Science and Technology Area) of the Department of Agricultural and Food Sciences of the University of Bologna (DiSTAL; http://www.distal.unibo.it/it/ricerca/ambiti-di-ricerca/scienze-e-tecnol…) has been studying the properties of vegetable oils for several years. Recent investigations concern the increasing suspected distribution of fraudulent (non-genuine) extra virgin olive oil. Such extra virgin olive oil appears to be a blend of genuine oil and oil produced from low-quality olives and subjected to a low temperature deodorization treatment, an illegal procedure in the production of extra virgin olive oil.

The aim of this ‘soft deodorization’ is to eliminate flavours derived from low-quality olives or from inappropriate procedures during oil extraction or storage, which are considered defects for extra virgin olive oils. Oil analysts have had difficulty in detecting this adulteration, which was the object of discussion in the recent scientific workshop on olive oil authentication (Madrid, 10–11 June 2013, http://ec.europa.eu/agriculture/events/olive-oil-workshop-2013_en.htm).

Many efforts by Italian and Spanish researchers have resulted in a new method capable of detecting the presence of marker compounds, fatty acid alkyl esters (AEs), present in appreciable amount in low quality virgin olive oil. These molecules are formed in oil derived from degraded olives and resist the soft deodorization procedure. This method was recently adopted by the International Olive Council (IOC) and then recognized by the European Union (EU Reg. 61/2011 then amended by EU Reg. 1348/2013).

Experiments carried out by the DiSTAL researchers, in collaboration with colleagues from the DiSTAM (Department of Food Science, Technology and Microbiology) of the University of Milan and DIAL (Department of Food Science) of the University of Udine, focused on different set of samples, both commercially available extra virgin olive oils sold at medium-to-low prices and genuine oils sampled directly from oil mills. All samples underwent the official AE analysis, with a first phase of marker separation and purification and a second phase of analytical determination.

Two new analytical approaches of analysing oils developed by the researchers are based on 1) spectroscopic analysis in medium infrared spectrum (ATR-FT-MIR), and 2) spectroscopic analysis by time domain reflectometry (TDR), which is used to measure the dielectric properties of different types of liquids.* The new methods fit well with strategies aimed at reducing timely procedures and minimising the use of expensive solvents that may be hazardous to not only the operators but also the natural environment.

Overall, by taking into consideration the legal limits of AE adopted by official regulations, these researchers found that some products on the market exceed these parameters. With respect to the official method to determine AEs, the new analytical approaches, are quicker, non-destructive and compatible with in-line use and permit a rapid screening.

Based on these preliminary results, carried out on a limited number of samples, the new analytical methods produce a satisfactory reliability rate and a high speed of analysis execution. Moreover, they were conducted without the use of chemical solvents, making it suitable for applications by all operators of the oil sector.

Alessandra Bendini
University of Bologna
www.atomiumculture.eu

 

*In both cases, chemiometric elaboration of the results using modelling tools and classification methods was applied to the spectral data and published in 2013, respectively, in the International Journal of Food Science and Technology, 48 (3), 548–555 and the Journal of Agriculture and Food Chemistry, 61, 1091910924.

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