Detection of Olive Oil Adulteration with vegetable Oils Using Spectrophotometer in Ultra Violet range and Gas Chromatography

Husam Mustafa ako
General Commission for Scientific Agricultural Research ،Department of Food Technology
Faculty of Agriculture,Damascus University,
2007

Summary

 This research is aiming to support the method of determination olive oil adulteration, which has been used in Syria to become more accurate and efficient by:

  1. Studying the ability of using the method of spectroscopy in ultra violet rang in order to improve the Gas Chromatographic technique in detecting the olive oil adulteration.
  2. Studying the changes on percentages of fatty acids in pure olive oil when it is mixed with other vegetable oils by using Gas chromatographic technique.
  3. Explaining the reason of changes by using statistical models to figure out mathematical formula, which facilitates comparing of fatty acids in regular range.
  4. specifying the relationship between the percentages of fatty acids and UV absorption
  5. Comparing the efficiency of spectroscopic and chromatographic method in detecting olive oil adulteration.

 73 samples have been tested, included pure virgin olive oil and four vegetable oils were used in adulterating and the mixtures which were formalized by mixing pure olive oil with vegetable oils (Corn, Soya bean, Sunflower, cotton oil) by percentages of 5%, 10%, 20%, 30%, 40%. The test of each sample was repeated three times. The previous samples were analyzed by spectrophotometer in ultra violet range at wavelengths 232nm, 266nm, 270nm and 274nm, ∆K value (alterative of variation of the specific extinction at the wavelength of maximum absorption near 270 nm) and R value (E270nm /  E232nm) were calculated. In addition, the samples were analyzed by Gas Chromatography device to determine the type and percentages of fatty acids for each sample.

 The results of samples analysis by spectroscopy technique showed the ability of using ∆K value to detect the adulteration of Olive oil up to 6.5 ±0.004%, 4.4 ±0.004%, 0.8 ±0.006%, 0.08 ±0.005% for each Soya bean, Corn, Sunflower, cotton oil subsequently. While these values at wavelength 270nm were 5 ±0.048%, 5.8 ±0.048%,             1.1 ±0.077%, 2.6 ±0.053% for each Soya bean, Corn, Sunflower, cotton oil subsequently. The absorption value at wavelength 232nm did not show any sign in detecting the adulteration. Meantime the minimum detection percentages of adulteration with R-value were     20 %, 10% for Corn and Soya been oil, Cotton and Sunflower oil subsequently.

The results of samples analysis by Gas Chromatographic technique showed the ability of detecting olive oil adulteration at rates higher than  25%, 10%, 13%, 5.5% for  corn, Soya beans, sunflower and cotton oil subsequently, with ability to specify  the type of adulterating oil which mixed with olive oil relying on fatty acids: Linolenic acid, Myristic acid and Behenic acid which recognize the Soya been, Sunflower, and Cotton oil subsequently. Meanwhile, The method wasn’t certify any fatty acid recognized corn oil, so it was hard to defined the  adulteration with this oil before make sure that the adulterating oil isn’t one of other three adulterating oils ( Soya been, Sunflower or Cotton oil).

Results did not show any relationship between the absorption values at wavelengths 232nm and 270nm and the percentage of Linolenic acid and Linoleic acid subsequently.

  • The value of ∆K considered as the most effective sign in determination of adulteration of olive oil, which mixed with low rates of vegetable oils in comparison with values E270nm, E232nm and R by using spectroscopy in ultra violet range.
  • Gas chromatography method showed that the Oleic acid, Linolenic acid, Behenic acid and Myristic acid are recognize for each of olive oil, Soya been oil, sunflower oil, and cotton seed oil subsequently.

Emphasize on use UV method rely on ∆K value for detecting the adulteration of Olive oil mixed with low percentages of vegetable oils, and recommend using GC method rely on the percentage of Linolenic acid, Myristic acid, Linoleic acid and Behenic acid for distinguishing adulterating oil.