Analyzing Olive Oil Purity with Ultraviolet Spectroscopy Using the UV-1800 Spectrophotometer

People have started to realize the health benefits offered by olive oil and in recent years there has been an increasing demand for this product. However, the purity of olive oil has always been the subject of controversy and based on this aspect, olive oil has been classified as “Olive Oil,” “Virgin,” and “Extra Virgin.” Extra virgin has been considered as the top grade of olive oil by the United States Department of Agriculture (USDA) and the International Olive Council (IOC).

To evaluate olive oils, chemistry standards have been created. This article discusses the application of the Shimadzu UV-1800 spectrophotometer in the evaluation of olive oils. IOC’s COI/T20/Doc. no. 19 has described the analytical procedure based on olive oil’s absorption characteristics in the ultraviolet region using a spectrophotometer.

Ultraviolet Spectroscopy

The level of oxidation of olive oil can be determined using ultraviolet spectroscopy. The olive oil quality can be examined based on the absorption band range of 200-300nm. The presence of peaks in this region represents the existence of conjugated diene and triene systems. The principle of the analytical procedure is that the oxidation of oils leads to the formation of conjugated double bonds. The high degree of UV absorbency reveals that the oil has undergone oxidation (Figure 1).

Ultraviolet spectra of Extra Virgin Olive Oil and Olive Oil diluted in iso-octane using COI/T20/Doc. no. 19.

Figure 1. Ultraviolet spectra of Extra Virgin Olive Oil and Olive Oil diluted in iso-octane using COI/T20/Doc. no. 19.

The Shimadzu UV-1800 Spectrophotometer

The Shimadzu UV-1800 spectrophotometer (Figure 2) features a compact Czerny-Turner monochromator. The double-beam UV-Vis spectrophotometer is a compact instrument capable of being operated as a stand-alone instrument or in conjunction with UVProbe software. The USB-memory-ready spectrophotometer allows users to record the results to the USB memory for subsequent data analysis and printing on a computer.

The Shimadzu UV-1800 spectrophotometer

Figure 2. The Shimadzu UV-1800 spectrophotometer

Experimental Procedure

As described in COI/T20/Doc. no. 19, the dilution of olive oil samples was carried out using iso-octane (2,2,4- Trimethylpentane). This was followed by a sample measurement on the Shimadzu UV-1800 with the help of 1cm path length quartz cuvettes. The reference solution was the solvent used. Spectrophotometric analysis of the olive oil was performed using the official procedures outlined in the EC regulations. As per the procedure, the specific extinction (extinction coefficient) in iso-octane at different wavelengths, including 232, 264, 268, 272nm, was determined. Then, the variation of the specific extinction (ΔK) was determined. The corresponding equations are as follows:

       Kλ = Eλ/c.s

Where, Kλ = Specific extinction at wavelength λ; Eλ = Extinction measured at wavelength λ; c = concentration of the solution in g/100mL; and s = Thickness of the cuvette in cm.

       

Where, Km = specific extinction at wavelength m (268).

The extinction coefficients of five different samples of olive oil, designated as either “Olive Oil,” and “Extra Virgin Olive Oil,” were measured using the Shimadzu UV-1800.

Experimental Results

The analysis results of multiple olive oil samples using the UV- 1800 and their correlation to the specifications described by the IOC standards are summarized in Table 1.

Table 1. Specific extinction coefficients measured on the Shimadzu UV-1800 for Extra Virgin Olive Oil and Olive Oil samples.

Measured K Values
Olive Oil Sample Type K232 K264 K268 K272 ΔK
Extra Virgin Sample 1 2.379 0.179 0.173 0.165 0.001
Extra Virgin Sample 2 1.911 0.207 0.214 0.209 0.006
Extra Virgin Sample 3 2.085 0.130 0.135 0.134 0.003
Olive Oil Sample 4 2.373 0.686 0.759 0.663 0.085
Olive Oil Sample 5 2.180 0.701 0.772 0.675 0.084
Criteria K Values
Extra Virgin Olive Oil ≤ 2.50 ≤ 0.22 ≤ 0.01
Olive Oil - ≤ 0.90 ≤ 0.15

With the help of Shimadzu’s UVProbe software, bespoke procedures and pass/fail criteria can be created and saved for future use in accordance with the IOC standards (Figure 3).

Create custom equations for calculating the specific extinction coefficients and establish Pass/Fail criteria based on outlined IOC standards.

Figure 3. Create custom equations for calculating the specific extinction coefficients and establish Pass/Fail criteria based on outlined IOC standards.

Conclusion

The results demonstrate the ability of the Shimadzu UV-1800 spectrophotometer to perform purity analysis of olive oil samples, thereby enabling to differentiate between Olive Oil and Extra Virgin Olive Oil as described by the IOC standards. The experimental results can be efficiently analyzed and interpreted with the help of the UVProbe software for correlation with standard values.

This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.

For more information on this source, please visit Shimadzu Scientific Instruments.

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Comments

  1. Sarah omar Sarah omar Libya says:

    in some other reference we find  the relation as 1000[k268-0.5(k262+k274)] ... why you exclude 1000 in your equation ... thank you

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