Olive Oil 

The olive trees are a traditional crop of the Mediterranean landscape with olive oil being the primary source of fat and one of the major components of the Mediterranean diet [1]. The major components of olive oil are the fatty acids, of which oleic acid (mono-unsaturated fatty acid) represents 55 to 83%, linoleic acid (poly-unsaturated fatty acid) represents 4 to 21% and palmitic acid (saturated fatty acid) represents 7.5 to 20%, see Figure 1. Owing to the high amount of mono-unsaturated fatty acids, olive oil has antioxidant and anti-inflammatory properties and is essential to reduce bad cholesterol levels, therefore decreasing the risk of cardiovascular diseases [2].

Figure 1 – Rule Gratings

The International Olive Council regulates the different qualities of olive oil, a parameter that can be determined by the amount of acidity. The acidity measures the rate in weight of the free fatty acids over the total amount of olive oil. The highest quality olive oil is classified as extra-virgin and is a chemically unprocessed olive oil that never exceeds an acidity level of 0.8 %. Virgin olive oil, on the other hand, has an acidity level that should never exceed 2 degrees. Olive oil with an acidity level higher than 2% is termed lampante and is not suitable for consumption [3].

Oxidation is a deteriorative process that involves primarily unsaturated lipids and plays an important role in lowering the oil quality. The primary products in unsaturated lipid oxidation show diene or triene conjugated double bonds that result from the changes in the linoleic acyl groups. These changes in the acyl groups modify the properties of the fatty acids, therefore affecting the olive oil quality. The oxidized fatty acids products show a strong absorption at around 270 nm. For the assessment of the olive oil quality, EEC Regulation 2568/91 (1991) outlines a method using UV-Visible spectroscopy [4]. In this application note, we combine the DWHP light source with a FLEX spectrometer in an UV-Visible configuration to determine the quality of three samples of labeled extra virgin olive oil.

Figure 2 – Holographic Gratings

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The amount of dispersion (also known as groove density or groove frequency) is usually expressed in nm/mm and determines the range of wavelengths that are dispersed by the grating into the detector. It increases with the increase of the groove density (lines/mm), which allows an improvement of the resolution for a certain slit width. On the other hand, groove density also defines the operational range of wavelengths of the grating being, therefore, an important parameter not only to determine the optical resolution of the spectrometer but also to set the range of wavelengths in which it works. In this sense, increasing the groove density (higher than 1200 lines/mm) leads to a higher spectral resolution value and a small operational wavelength range of the spectrometer. In contrast, decreasing the groove density (lower than 1200 lines/mm) leads to a lower spectral resolution value and a higher operational wavelength range of the spectrometer, see Figure  3.

Figure 3 – Absolute efficiency curve of two holographic gratings, the first with 600 grooves/mm (orange line) and the second with 1800 grooves/mm (blue line).

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The amount of dispersion (also known as groove density or groove frequency) is usually expressed in nm/mm and determines the range of wavelengths that are dispersed by the grating into the detector. It increases with the increase of the groove density (lines/mm), which allows an improvement of the resolution for a certain slit width. On the other hand, groove density also defines the operational range of wavelengths of the grating being, therefore, an important parameter not only to determine the optical resolution of the spectrometer but also to set the range of wavelengths in which it works. In this sense, increasing the groove density (higher than 1200 lines/mm) leads to a higher spectral resolution value and a small operational wavelength range of the spectrometer. In contrast, decreasing the groove density (lower than 1200 lines/mm) leads to a lower spectral resolution value and a higher operational wavelength range of the spectrometer, see Figure  3.

Figure 3 – Absolute efficiency curve of two holographic gratings, the first with 600 grooves/mm (orange line) and the second with 1800 grooves/mm (blue line).

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Get a resumed information about the purity of olive oil samples using UV-Visible spectroscopy

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