Two monovarietal extra virgin olive oils (Arbequina and Coratina), produced in Uruguay, were studied over a period of 12 months storage in amber bottles at 30 º C. Peroxide index, K 232 , K 270 , ∆K, OSI induction time did not exceed the maximum limits set by the International Olive Council (IOC) during the entire period. However, the content of ethyl esters increased with storage time and it is in relation with the shelf life. The International Olive Council (IOC) establishes the limits in the content of ethyl esters ≤ 35 ppm. The Coratina oil ceased to be extra virgin quality after 6 months of storage due to its content of ethyl esters (46 ppm), and the Arbequina oil after 9 months (52 ppm).Taking into consideration their content of ethyl esters, both the Arbequina and Coratina oils showed a very short shelf life less than six months. The determination of ethyl ester content proved to be a sensitive method for determining the loss of quality of extra virgin olive oils.

No abstract

Extra virgin olive oil is recognized as a very stable oil because of its composition in fatty acids and its content in natural antioxidants (tocopherols and polyphenols). In the bibliography are works that address different aspects of this stability, from the duration of its useful life to its performance in the frying of foods. Some works also link their stability with the content of natural antioxidants. For example, Franco et al. (2014) studied the content of phenols and their antioxidant capacity in olive oils of seven different varieties. Baccouri et al. (2008) found a good correlation between the oxidative stability (measured in Rancimat) of the oils studied and the concentration of total phenols and tocopherols.

Fatty acids' ethyl and methyl esters are not natural components of edible vegetable oils and therefore should not be present in virgin olive oils. Among the quality requirements for extra virgin olive oils, the International Olive Council (IOC) Norm, 2015 review, set limits for the ethyl ester content at ≤ 435 ppm for the 2014/2015 and 2015/2016 harvests and at ≤ 30 ppm for the 2016/2017 harvest. The purpose of this paper is to: (a) determine the alkyl ester content in two extra virgin olive oils (of the Arbequina and Coratina varieties) as parameters of quality at the moment of their elaboration and to assess the length of their shelf life, over a 12 month period at room temperature; (b) determine extra virgin olive oils' free alcohols content as these may esterify due to the free fatty acids present during storage. After 6 months of storage, the Arbequina oil's ethyl ester content was 32 ppm, and the Coratina's was 46 ppm. As a result, the shelf life for both was only about half a year (labeling usually indicates it must be consumed "before 1 year"). However, parameters related to oxidation (peroxide index, K 232, K 270 and ∆K) remained within the limits set by the International Olive Council (IOC) throughout the year. In conclusion: ethyl ester content is a very fine parameter for assessing the quality of extra virgin in an olive oil and determining the length of its shelf life.