Adulteration Detection in Syrian Virgin Olive Oil Using HPLC (Triglycerides), GC/MS (Volatiles) and Reagents (Colors)

Zainab Ibrahim Al-Nasan
General Commission for Scientific Agricultural Research- Department of Food Technology,
Faculty of Agriculture,Damascus University,
2009

Abstract

This study included three experiments, which aimed particularly to detect adulteration in Syrian virgin olive oil. These experiments were Triglycerides analysis by HPLC technique. Flavor compound analysis by GC or GC-MS technique were applied in the laboratory. A spontaneous and quick test is needed for field analysis of any possible adulteration process, carried out on virgin olive oil inside the mill (field). This test enables the researchers and the buyers to determine the olive oil purity, before purchasing and storage. Hence, this experiment based on developing color reagent that reveals any color changes in the tested olive oil when it is used.

In the first experiment individual triglycerides (TG) species were separated and identified qualitatively and quantitatively from the following samples:

  1. Syrian virgin olive oil (SVOO) from the Governorates (Edleb, Homs, Latakia, Dara’).
  2. Adulterating plant seed oils (APSO) (soybean, corn, sunflower, cottonseed).
  3. A mixture of each adulterating plant seed oil at certain percentages (1.0, 2.5, 5.0, 10.0, 20.0% w/w) with the virgin olive oil of (Edleb, Homs, Latakia, Dara’). Three replicates of each sample were used, and a total of 264 samples have been tested. An adulteration of Syrian virgin olive oil with these APSO could be verified by detecting any significant changes in virgin olive oil TG species.

The TG analysis was achieved by the reversed-phase, High-performance liquid chromatographic (RP-HPLC), refractive-index detector (RI) and ODS1 column. Upon analysis, it was found that some TG species can be used as markers for adulteration. Hence, it was concluded that:

  1. The TG species of LLL, LOL and PLL were normally presented at very low levels in SVOO (0.18-0.32%, 1.94-3.55, 0.51- 1.14%) respectively, while they were presented at very high levels in the adulterating oils (28.00- 16.43%, 20.71- 12.84%, 21.32- 13.40%) respectively. These three TG species were used as markers to detect adulteration of virgin olive oil, by the observation of any increase in there levels.
  2. Trilinolein (LLL) in SVOO was presented as a marker at a very low level (<0.50%), Furthermore, this marker was used by the IOOC as an indication of adulteration in virgin olive oil, too.

The First test- Triglycerides analysis:

  • Statistical analysis showed that the percentage of LLL in SVOO of Latakia was, significantly, higher than those in SVOO of Edleb, Homs, and Dara’. And the percentages of LOL, and PLL in SVOO of Edleb were significantly lower than in SVOO of Homs, Latakia and Dara’. An adulteration of SVOO from Edleb, Homs and Dara’ with low content (≥50% w/w) of adulterating oils (except sunflower oil) could be detected, significantly. An adulteration of SVOO from Latakia with low content (≥ 1.00% w/w) of adulterating oils could be detected, significantly.
  • The percentage of LLL, LOL and PLL in adulterating oils were very high. Statistical analysis showed that the percentage of LLL in sunflower oil was significantly higher than in other adulterating oils. An adulteration of SVOO with low content (≥0% w/w) of sunflower oil could be detected by any increase in the LLL, LOL, PLL levels.

Moreover, The use of  RP-HPLC method for the triglycerides analysis has the advantage of one- step analysis and it is done by diluting the studied oil with aceton at (5% w/v). Low cost and less time are needed for this analysis, hence improving the economical efficiency.

The Second test- Color reagent analysis:

General color reagent for olive oil adulteration detection has been developed with specific ability of 10% detection of the adulterating oil. This test can be implemented at the mill as well as at the lab.

The Third test – Volatile compound analysis:

It is possible to analyze and use special markers of all the volatile compounds extracted from the SVOO, APSO and the mixture. In order to detect any changes in these markers, GC and GC-MS are used for this analysis. However, this analysis was not applied because the GC-MS was not available.