- Oxidative stability, one of the most important factors to determine olive oil quality, is clearly influenced by the fruit ripeness degree

- The evaluation used two main monovarietal Tunisian cultivars, cvv. Chétoui and Chemlali virgin olive oils

- The chemical composition of virgin olive oil may be influenced by genotype (internal) and different agronomic and technological (external) factors

Extra virgin olive oil is considered to be the best olive oil for its organoleptic characteristics, for its oxidative stability and its chemical composition. It is practically the only vegetable oil that can be consumed directly in its raw state and contains important nutritional elements (vitamins, antioxidants, etc.).

The study was carried out in 2007 at the Laboratoire Caractérisation et Qualité de l’Huile d’Olive, Centre de Biotechnologie de Borj-Ce´dria, Tunisia, and the Dipartimento di Scienze degli Alimenti, Università di Bologna, Italy; the paper was published in 2008 in the journal Food Chemistry.

A prominent chemical composition

Virgin olive oil is composed of triacylglycerols (around 97–98%), minor variable amounts of free fatty acids and minor glyceridic compounds and around 1% of constituents of varied structure and polarity. The oxidative stability, sensory quality and health properties of virgin olive oil stem from a prominent and well-balanced chemical composition. In fact, the high content of oleic acid in olive oil serves to slow down penetration of fatty acids into arterial walls.

Oils which are much higher in monounsaturated fatty acids and lower in saturated fatty acids are preferred because of the proven beneficial effect on serum cholesterol levels. The biological properties of olive oil are also related to the presence of minor components, antioxidant compounds. In particular, among the natural antioxidants, phenolic compounds are reported to play a key role in preventing oxidation and have been already correlated to the storage stability of virgin olive oils.

A matter of genes… and circumstances

The chemical composition of virgin olive oil may be influenced by genotype and different agronomic (i.e. fruit ripeness degree, water supply) and technological factors. This research reports the evaluation of the influence of the olive ripening stage on the quality indices, the major and the minor components and the oxidative stability of the two main monovarietal Tunisian cultivars (cvv. Chétoui and Chemlali) virgin olive oils. Moreover, the olives cv. Chétoui were tested in a rain-fed control and an irrigation regime. The oils sampled at five different ripeness stages were submitted to different analysis. Moreover, the triacylglycerol and fatty acid compositions, and minor components, pigments and their relation with the oil oxidative stability were evaluated. The tested oils showed very good correlation between the oxidative stability and the concentrations of total phenols.

The chemical data discussed in this work can be considered useful in providing information about the presence in the oil of major and minor compounds of the two main Tunisian cultivars for what concerns the increase of olive ripening. The analytical parameters studied remained widely within estimated limits of the regulation throughout the maturity process. Nevertheless, this research evidenced that the oleic/linoleic acid ratio shows a decreasing trend as the olives ripened. With regard to phenolic compounds, Chétoui had the highest stability value. Finally, the present work shows in Chétoui EVOO, the anticipate harvest-date, gave the best results in terms of all the parameters considered. Instead, for the cv. All that data could be used to define the ideal ripening degree to confer a good balance between chemical profiles. Additional works will be addressed to assess how these cultivars can be grown in other olive growing districts in order to separate the genetic effect from the environmental factor.

Source: Food Chemistry http://www.elsevier.com/wps/find/journaldescription.cws_home/405857/description?navopenmenu= 1

Reference: Oleociencia. – www.oleociencia.com