The concentration of the compounds in the volatile fraction of extra virgin olive oil depends on the level and activity of the enzymes which are genetically determined, as well as the climate and type of soil as well as the ripening cycle of the fruit. Removal of the stone during extraction is another factor that influences volatile compounds.
The quality of olive oil is sometimes reduced by attacks of leprosy: the pathogen infects the fruit causing it to rot with negative effects on the quality and flavor of the oil.
Numerous studies have been conducted on the headspace composition of virgin olive oil obtained from oil of typical and non-typical Calabrian cultivars, but a direct comparison between the two is not possible since the oils are obtained from olives with different origins and different processing methods.
Such a complex interaction of factors requires a systematic approach, fixing the same variables, to understand the development of volatile compounds of virgin olive oils produced by different cultivars grown in the same pedoclimatic conditions, with leprosy attack and after stone removal.
Samples of virgin oil were obtained from olives from the Leccino, Pendolino, Ciciarello, Nocellara, Coratina, Carolea and Ottobratica cultivars grown in Italy at San Giorgio Morgeto 500 m above sea level
From the different varieties of olive trees to the aromatic differences of extra virgin olive oil
All oils obtained contain volatile compounds derived from the biochemical lipoxygenase pathway which allows the catalytic oxidation of 1–4 pentadienic structures to give C6 derivatives.
In particular E-2-hexenal, and hexanal, derived from the heterolytic degradation of the 13-hydroperoxide of linoleic and linolenic acid respectively, catalyzed by enzymes involved in the hydroperoxide lyase reaction.
C5 compounds derived from the breakdown of the alkoxy radical are also present.
In the oil obtained from the varieties Ciciarello and Pendolino, the high content of 1-hexanol and E-2-hexen-1-ol can be attributed to the increased presence or activity of the enzyme alcohol dehydrogenase (ADH). ADH has previously been reported as the enzyme responsible for the biosynthesis of six-carbon alcohols (1-hexanol, E-2-hexanol, and Z-3-hexenol). In these varieties there is also the effect of Alcohol Acetyl Transferase (AAT), an enzyme that produces hexyl acetate from hexanal and Z-3-hexenyl acetate from the corresponding alcohol Z-3-hexenol.
In the oil obtained from cultivars Pendolino, Nocellara and Leccino the main effect of volatile compounds can be attributed to the ADH enzyme while the AAT enzyme has very little effect.
In variety Coratina the ADH enzyme is poorly active, hence a high concentration of E-2-hexenal. The AAT enzyme appears not to be active in this strain.
It is evident how the quantity of volatile compounds is influenced by the enzymatic activity. This is demonstrated by the close correlation between the concentrations of the ratios E-2-hexen-1-ol/E-2-hexenal and 1-hexanol/hexanal, the former substrates and the latter the products of the ADH enzyme.
Oil obtained from pitted olives from two different varieties have shown that the higher content of volatile compounds compared to that obtained from whole olives are independent of the variety.
This methodology could solve the problem of the lack of headspace components of some cultivars and therefore of the aroma for oils obtained from industrial processes in which hot water is added during the extraction phase.
The oil obtained from olives affected by leprosy has high values of hexanal, octanal and nonanal aldehydes, due to the high oxidation state of the oil.
From the results obtained it is not possible to distinguish only oils obtained from different varieties on the basis of the content of volatile compounds in the headspace.
The SPME, GC and PCA methods can discriminate oils obtained from pulp alone, those from leprosy-damaged fruits and commercial batches.
Bibliography
Runcio, A., et al. “Volatile compounds of virgin olive oil obtained from Italian cultivars grown in Calabria.: Effect of processing methods, cultivar, stone removal, and anthracnose attack.” Food Chemistry 106.2 (2008): 735-740.
