Year 12 | 28 January 2020 | email@example.com
Yes, extra virgin olive oil contains some water, whose role is important in helping solving the more polar anti-oxidants and supporting their action. With Lercker’s and Cerretani’s help, let’s follow the way from olive to bottled olive oil
It is recognized the relevance of the so-called “minor components” (that is to say components present in very scarce concentration) in characterizing virgin and extra virgin olive oils. These components include anti-oxidant compounds, healthy elements and all substances responsible for the sensorial features of the oil. These three effects are in particular typical of the phenolic compounds .
These compounds have received much attention not only by the research world, but also by popular media, in the last few years. Researches about the phenolic compounds of extra virgin oils have been and are being carried out by researchers coming from different countries and are centered around diverse issues, typical of contexts varying from food science to medical research. The first experimental observations of the presence of these compounds in virgin olive oils date back to more than one hundred years ago and were made by the Italian chemist Francesco Canzoneri (1906) .
During this century, several researches have been carried out and a role has been attributed to the interaction between phenolic compounds and other micro components of virgin and extra virgin oils. In particular, the presence of water was observed [3,4]. Water content in olive oil varies from 300 to 2000 mg per kg of oil, often more than the “saturation” threshold (300-400 mg per kg of oil). This water is present in forms of micro drops dispersed in the oil, which are stabilized by the aggregation-dissolution of a group of polar substances, water-soluble and/or water-compatible, such as mineral salts, free acids, digicerids, phospholipids, alcoholic and phenolic substances. This is a dispersion (fine emulsion, or micro emulsion), not a suspension, since it is impossible to separate oil and water.
Figure 1 shows two microscope pictures (zoomed 1600x)during the defrosting of two olive oils, the first one (A) containing approximately 1200 mg of water per kg of oil, the second one (B) about 250 mg of water per kg of oil. Picture A shows the uneven contour of the fat drops, whose conformation is due to the presence of water drops, while picture B shows fat drops with more regular profiles because of the low content in water.
As anticipated, the role of the water in oil can be identified in its capability of solving salts and other small or medium sized organic molecules, this favoring their presence in systems ill-suited to contain polar compounds, and stabilizing their presence in suspension, dispersions and colloidal dispersions. In particular, such an effect is highly relevant in the light of the chemical features of phenolic compounds and their aforementioned role in virgin and extra virgin oils.
Another role of water regards its action on typical organoleptic features, that water exercises in watery solutions or dispersions in hydrophobic matrices. Generally speaking, the organoleptic sensation perceived with the taste and related to the smell of a food, are conditioned by the presence of water and the form of its presence. The taste is perceived by the sequence of contacts of the molecular structures in the food, which is modulated by their localization in the watery and organic phases, privileging first of all the contact with the water phase, which is consistent with the fact the our tongue’s taste buds are wet with water (saliva).
Let’s follow the way of water during the process of production of oils.
Water is the main component of the fruit of the olive tree, being about half of its total weight. The first operation made directly is the fruit crush, aimed at set the oil micro drops free, thus determining the contact with all the components of the fruit; at this stage, the quickest and most energetic systems induce the dispersion of oil drops, but also water ones. The following stage, represented by the malaxation, whose main goal is allowing the oil drops to aggregate in larger and larger drops, so that separating them from the other components can be more easily achieved; this operation determines other secondary processes which are highly relevant for the characteristics of oils: for instance, one of them is the formation, through enzymatic processes, of volatile compounds which are responsible for the olfactory sensations.
The other important phenomenon which takes place during malaxation is the transformation of phenolic compounds in those glycosilate forms which are most common in the fruit and in forms deprived of sugar, characterized by less polarity and thus a higher compatibility with the oily phase where water is present in micro emulsion. At this stage, the aggregated oil is very rich in emulsified water. The separation by means of the decanter separates water and oil; some observations showed that biphasic systems help this separation. The last stage of the separation is operated by the vertical separator, which eliminates the excess water. At the end, the oil appears veiled because of the remaining micro emulsified water.
At this point, the filtration and preservation processes directly act on the content of this micro emulsified water and, consequently, on the overall features of oil. As to the filtation, the more water is maintained, the more the compounds solved in it are reduced in concentration; hence, the filtration on cotton is considered one of the more drastic for the capability of cotton to retain water. A filtration system without any adsorbing substratum permits to reduce the loss of water and compounds solved in it.
During the conservation several phenomena can affect water stability, first and foremost temperature control. Sudden changes in temperature destabilize water and in particular, this effect can be stressed by the low temperature of crystallization of oil, whose first outcome is the separation of water and a partial aggregation at the restoration of the liquid phase. Experimental studies showed that partial crystallization can occur below 12°C, especially in oils characterized by a low content in polyunsaturated fatty acids. Therefore, a good storage temperature can fall in the range 12-15°C, to be controlled by air conditioning systems .
Back to where we started from, almost the totality of the water in the fruit, plus the process water, represents a sub-product to eliminate at the end of the production process. This water dissolves several compounds present in the fruit, such as most of the phenolic compounds which result more affine to water than oil because of their high polarity and the presence of sugars.
As regards the use of vegetation water instead of water network supplied water in the plants where three or two and a half (“eco” process) phases processes are performed, it has been observed that a potential enrichment in dispersed water and phenolic substances would also generate foul-smelling compounds during the fermentation, even for reduced working times.
1. A. Bendini, L. Cerretani, A. Carrasco-Pancorbo, A. M. Gómez-Caravaca, A. Segura-Carretero, A. Fernández-Gutiérrez, G. Lercker. "Phenolic Molecules in Virgin Olive Oils: a Survey of Their Sensory Properties, Health Effects, Antioxidant Activity and Analytical Methods. An Overview of the Last Decade" Molecules 12: 1679-1719 (2007) http://www.mdpi.org/molecules/papers/12081679.pdf
2. A. Carrasco-Pancorbo, L. Cerretani, A. Bendini, A. Segura-Carretero, T. Gallina Toschi, A. Fernández-Gutiérrez "Analytical determination of polyphenols in olive oils" J. Sep. Sci. 28: 837-858 (2005).
3. G. Lercker, A. Bendini, L. Cerretani. "Qualità, composizione e tecnologia di produzione degli oli vergini di oliva" Progr. Nutr. 9: 134-148 (2007).
4. L. Cerretani, A. Bendini, S. Barbieri, G. Lercker. "Osservazioni preliminari riguardo alla variazione di alcune caratteristiche chimiche di oli vergini da olive sottoposti a processi di deodorazione "soft"". Riv. Ital. Sost. Grasse 85: 75-82 (2008).
5. M. Bonoli-Carbognin, L. Cerretani, A. Bendini, T. Gallina Toschi, G. Lercker "Prove di conservazione a diversa temperatura di olio da olive monovarietali" Ind. Aliment.-Italy 452: 1135-1141 (2005)
by Lorenzo Cerretani
02 february 2009, Technical Area > Olive & Oil