Comparing the use of barcode DNA length polymorphisms and fatty acid profiling for detecting adulteration in olive oil -

Comparing the use of barcode DNA length polymorphisms and fatty acid profiling for detecting adulteration in olive oil.

Introduction:

The global demand for olive oil is increasing due to its popularity as a natural, minimally processed, and phytochemical-rich food product. However, the high price of cold-pressed extra virgin olive oil makes it a target for adulteration with cheaper seed oils. This fraudulent practice poses both economic and health risks, as adulterants may be allergenic or toxic. Traditional authenticity assessments rely on analytical chemistry methods, such as fatty acid profiling, which may not always be effective for minor oil constituents. DNA-based methods, utilizing the plastid genome, have emerged as a promising tool for authenticity testing in olive oil. The PCR-capillary electrophoresis (PCR-CE) barcode assay, targeting the trnL (UAA) intron, shows potential for detecting small quantities of seed oil in olive oil-seed oil mixtures. This DNA-based approach is compared to the widely used analytical chemistry method of fatty acid profiling by gas chromatography (GC).

Methodology:

This study involved 11 plant oil samples, including two unrefined oils (olive and hazelnut) and nine refined oils (soybean, sesame, sunflower, rapeseed, corn, cottonseed, peanut, safflower, and palm oils). Reference tissue samples were obtained from various sources, and DNA isolation was performed using a NucleoSpin Plant II Kit for tissue and a Wizard Magnetic DNA Purification System for oils. The PCR-capillary electrophoresis (PCR-CE) barcode analysis targeted the plastid trnL (UAA) intron, and gas chromatography (GC) analysis was conducted after methyl esterification of oil samples. The study assessed DNA integrity, concentration, and barcode profiles, comparing the PCR-CE assay with GC analysis for authenticity testing of olive oil and seed oil admixtures.

Results:

This study aimed to assess the authenticity of olive oils by using a DNA-based approach, specifically the plastid trnL (UAA) intron. The research employed PCR-CE analysis to detect adulteration with ten different seed oil species. Results showed that the DNA-based assay effectively identified adulteration down to a 5% limit, outperforming traditional chemical analysis of fatty acid profiles. The PCR-CE method demonstrated species specificity, successfully detecting various adulterants, including soybean, palm, rapeseed, sunflower, sesame, cottonseed, peanut, corn, safflower, and hazelnut oils. The study highlights the superiority of the DNA-based assay in detecting fraud, providing accurate identification of botanical origin even in the presence of small quantities of adulterants. The sensitivity of the DNA-based assay makes it a valuable tool for ensuring the authenticity of olive oils in the face of potential adulteration.

Conclusion:

In conclusion, this study aimed to compare the efficacy of a DNA-barcode assay using the plastid trnL (UAA) intron with traditional fatty acid profile analysis for authenticating the botanical origin of olive oil. The PCR-capillary electrophoresis (PCR-CE) approach demonstrated comparable efficiency to gas chromatography analysis in detecting adulteration with various seed oils. Notably, the DNA-based assay outperformed gas chromatography in accurately identifying adulterant species and detecting small quantities of corn and safflower oils in olive oil. Additionally, the PCR-CE test successfully identified hazelnut oil adulteration, a task not feasible through fatty acid profile analysis. Overall, our findings emphasize the potential of the PCR-CE barcode assay as a robust method for detecting adulteration in olive oil.

Reference:

UNCU, A.T., UNCU, A.O., FRARY, A. AND DOGANLAR, S., 2017. Barcode DNA length polymorphisms vs fatty acid profiling for adulteration detection in olive oil. Food chemistry, 221, pp.1026-1033.