Abstract
Virgin olive oil is an important ingredient of the Mediterranean diet highly appreciated for its beneficial health effects due to the presence of mono-unsaturated fatty acids and antioxidant properties. The olive oil quality is defined by many parameters, among which acidity and peroxide index and according to international regulations, these two determinations are carried out in laboratory environment, by means of manual titration. This kind of method, however, cannot be used on oil production sites, where, instead, it would be desirable to know the main characteristics of the oil for proper product classification. In this paper, a new technique to measure olive oil acidity by electrical conductance is presented that allows for fast, cost-effective, and on-site measurements. Such a technique has been validated with a set of 55 olive oil samples. Two different oil emulsions have been used and compared for the measurements: based on a hydro-alcoholic solution (60% ethanol 40% distilled water) and distilled water, respectively. The data show that the electrical conductance of the emulsion with hydro-alcoholic solution is a strong function of the olive oil acidity, that can be estimated with good accuracy (R 2 =0.9308). The experiments with distilled water, instead, exhibit no significant correlation between oil acidity and emulsion conductance that, however, is found to provide information about peroxide index, polyphenols content, and filtration technique. Furthermore, using both types of emulsions to compensate for conductance variations other than free fatty acids the accuracy in acidity determination can be improved reaching R 2 =0.9786.
Highlights
O LIVE oil, produced from the olive fruit (Olea Europea L.) belonging to the family Oleaceae, represents an important ingredient of the diet and it is highly appreciated for its beneficial effects on human health, mainly due to a high content of oleic acid and polyphenols [1]
Olive oil samples differing only for acidity value have been artificially created by adding known concentrations of oleic acid to a commercial virgin olive oil
The measured electrical conductance Gm is plotted vs. acidity in Fig. 2 for the emulsion created with the hydro-alcoholic solution (a) as well as with distilled water (b)
Summary
O LIVE oil, produced from the olive fruit (Olea Europea L.) belonging to the family Oleaceae, represents an important ingredient of the diet and it is highly appreciated for its beneficial effects on human health, mainly due to a high content of oleic acid and polyphenols [1]. A study on worldwide patterns of cancer mortality [2] has shown how mortality from breast and colorectal cancer is lower in countries with higher olive oil consumption. Olive oil properties appear to reduce mortality from coronary heart diseases [3]. About 90% of the world olive oil production is from the Mediterranean basin with the European countries responsible for about 82% of the production [4]. Spain with over 320 million olive trees is the largest producer (37% of the world production), followed by Italy (24%) and Greece (22%). Other emerging olive oil producers are California (USA), Australia, New Zealand and Chile [5]
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