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Non-destructive monitoring the effects of light exposure on quality deterioration of extra virgin olive oils with fluorescence spectroscopy

Posted: 20 June 2016 | | No comments yet

Extra Virgin Olive Oil (EVOO), being an important source of antioxidants and healthy fats, is an economically important product of Mediterranean countries. Since EVOOs can only be produced during a limited period of time annually, in order to maintain its commercial availability throughout the year packaging materials such as glass, plastic and metals are used. The transparency of the glass and plastic materials exposes the oil to the natural light conditions leading to photosensitised oxidation. The oxidation of oils results in loss of minor chemical components that are responsible for sensory and nutritional quality.

Monitoring light exposure with fluorescence spectroscopy

The oxidative stability of EVOOs during storage is of high importance to prevent the formation of off-flavour compounds leading to its overall quality deterioration. To maintain the quality of EVOOs it is important to monitor the changes occurring during its storage and processing conditions. However, the monitoring of EVOOs’ quality is a complex analytical challenge due to the presence of complex mixtures of biochemical compounds such as triacylglycerol, partial glycerides, hydrocarbons, tocopherols, pigments, sterols, alcohols, triterpene acids, volatile compounds, phenolic compounds, phospholipids and proteins1. Typically, the oxidation of EVOOs leads to the formation of primary oxidation products such as hydroperoxides, which, further decompose to secondary oxidation products like aldehydes, alcohols and ketones2. These latter formed compounds are responsible for the characteristic ‘off-flavour’ of degraded oils. Previous work carried out with fluorescence spectroscopy proved it to be a cheap, quick, noninvasive tool to deal with quality monitoring of olive oils3,4. In fluorescence spectroscopy, by excitation with ultraviolet or visible light, the fluorescent molecule of interest is promoted to one of the several vibrational levels. Afterward, the molecule returns back to the ground state emitting fluorescence light at higher wavelengths than the excitation light. These emitted lights at particular wavebands correspond to biochemical equivalents and, therefore, allows the non-invasive monitoring of EVOOs.

In the present work, fluorescence spectroscopy was used to monitor the changes occurring in the EVOOs when exposed to light and when stored in dark conditions. Typically, when the EVOOs are exposed to light conditions, they undergo accelerated oxidation. This oxidation results in production of new biochemicals in the oil, which typically have characteristic fluorescence spectral signatures. Therefore, it was decided to identify different regions from the changes in the fluorescence spectra. The identified changes in the spectra were later used to explain the change in quality of EVOOs. Obtained results showed that the exposure of oils to light resulted in a rapid degradation of quality, whereas the oils that were stored in dark conditions showed minimal change in quality. Furthermore, in a fast and non-destructive manner, the fluorescence spectroscopy provided successful monitoring of the biochemical changes occurring in the EVOOs during storage time.

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