Year 12 | 26 January 2020 | email@example.com
It is one of the most striking and treacherous frauds. Alissa Mattei suggests what we can found in different oils
Because of my artistic nature, chemistry is not hard and difficult for me. So, while looking at extra virgin olive oil I found myself facing and incredible example of composition complexity that greatly stimulated my fantasy, my universal harmony and “chance and necessity” example research, as well.
In this research of natural equilibria, the shape in space of molecules holds a particular meaning. This is one of the main subjects of stereochemistry, one of the most fascinating matters that concern the study of natural substances. So, the various oil components, such as sterols, fat acids, bifenols, biphenyls, tocopherols, alcohols, esters, aldehyds and ketones, which most of people consider as strange and indecipherable words, are in reality “live molecules” with particular shapes and a peculiar functioning.
In the first years of my work, a close link between production and oil industry did not exist. So, oil was a product disjointed with its natural origin (olive) and, as a consequence, it was studies according to this view.
Only in 80s the quality of the produced was begin to be linked with the olive fruit, taking into account, in this way, the complex relationships that exist among the tree, the fruit and the oil. This new perspective opened a new systematic approach to the virgin olive oil analysis.
At that time, the oil was make principally up of triglycerides and the most complex element that could be analyzed in it was the stereoisomery cis-trans of fat acids and the position and number of double bonds in it.
Later, the attention of researchers was paid to the component analysis of the non-saponificable elements, beginning from sterols and erythrodiol and followed by aliphatic alcohols and waxes, in order to recognize the mixture of olive oil with seed or sansa oils.
The analysis methods and the frauds competed ones with the others in a rapid run: one invented a new method to highlight a fraud, another adulteration promptly arose.
One of the most noticeable frauds is the so-called “deodorized oil”. This very clever technique is well-known from years; with a very bland treatment (a child’s play!) it is possible to eliminate the unpleasant smells and tastes of fake oils.
In 1987 it was introduced the organoleptic examination that brought a great improvement in the virgin olive oil quality. However it was unable to fix such a fraud because of it was considered as a simple improvement of the Spanish “Lampantino” oil!
The systems that allow revealing the process of deodorization range from the tasting to simple or complex chemical-physical methods. As a matter of fact, by tasting the pure product it is quite simple to recognize fake oils, especially whenever the process was performed in sub-optimal conditions (the “baked” taste is typical of such a treatment). However, if the product is a mixture, it is a very much difficult.
From the chemical-physical methods viewpoint, they were first analyzed the changes in the lipid substrate. However, while for a normal deodorization (performed at 200-240°C in vacuum conditions or under a constant nitrogen flux) it is easy to verify the presence of neo-formed compounds, for the deodorization performed at lower temperatures (even below 100°C) with modern systems at intensive vacuum conditions and minimal deodorization times, it is really difficult to reveal neo-formed compounds. As a consequence, determine the presence of deodorization, especially in blend, is an extremely demanding challenge.
So, the analysis of position isomers (“trans” or “conjugate”, via HPLC) is not enough to single out a fraud. The same thing holds also for the analysis of pyropheophytins, 1-2, 1-3 diglycerides and alkilesters.
So, what we can say? A clever and experienced chemist is able to evaluate oil just analyzing the ensemble of chemical analyses and sometimes it is sufficient to verify a certain marker, whenever within the law limits, to highlight an anomalous case. It is obviously very difficult to transfer such experience into an automatic and reliable system.
Therefore, the problem “deodorization”, that sometimes can be also “washed”, i.e., treated with alkaline solutions in order to lower the resulting acidity, is far from being solved and the aforementioned parameters can be considered in general quality and not genuineness indexes.
So, if a bottling company wants to avoid imprudent purchases is should provide for very shrewd buying specifications in order to greatly limit the presence of treated oils. Hence, it is desirable to specify limitations in the total concentrations of 1,2 diglycerides, pyropheophytins, and alkilesters (also deriving from biophenols).
I conclude with a simple and interesting deepening about the diagnostic usefulness of the pyropheophytins analysis.
The nature of the natural evolution of the oil, which is mainly dependent on oxidation, produces the same variations as the thermic stress induced by deodorization. However, it is present a discriminating factor between the two origins which derives from the relationship between oxygenation and pyropheophytins production.
Besides the oxidative parameters (the peroxides index and the UV adsorption) are not exhaustive (the HPLC is better), they allow distinguishing between oxidated oil (corresponding to a high pyropheophytins and k270 level) and chemically treated oil (corresponding to a high pyropheophytins and a low k270 level).
Finally, as for the alkilesters determination, hold the considerations done for the other elements. As a matter of fact, a correlation between the concentration of such a molecule and quality does exist because of the deodorized oil is obtained from organoleptically imperfect oils, and then a correlation should hold with the deodorization process.
Summing up, we are still far from the determination of a clear parameter for distinguishing among extra virgin olive oils and deodorized oils, but, up to now, we can distinguish between and high quality oil and a low quality (possibly treated) oil.
by Alissa Mattei
02 march 2009, Technical Area > Olive & Oil