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Detection of GM Food (PROTEIN BASED)

Friday, July 9, 2010

1. Protein-Based

Immunoassay is the current method for detection and quantification of ‘new proteins introduced through genetic modulation of plants. The crucial component of an immunoassay is an antibody with high specificity and affinity for the target molecule. Immunoassays can be rendered highly specific and samples often need only a simple preparation before being analyzed. However, Protein-Based methods can only be applied if a new protein is expressed in GMO. Using the antisense or sense technology to suppress or overexpress the transcription/translation of a gene originated from plants does not result in a new protein. Even so, newly expressed proteins are usually varied in expression levels in different plant tissues. Thus the new protein may be express in very low levels, which may be below the detection limit.

Western Blot

It is a highly specific test method that provides qualitative results suitable for determining whether a sample contains the target protein below or above a predetermined threshold level. It is particularly useful for the analysis of insoluble protein. The detection limits of western blots vary between 0.1 and 1%. Sensitivity is dependent on the affinity level and level of expression of the protein in the plant.

Enzyme-Linked Immunosorbent Assay (ELISA)

it is a method to detect the presence of the specific protein that the genetically modified DNA produces in the plant.
Antibodies are used to react with specific proteins produced by the GMO. These are coupled to an enzyme, which catalyzes a color-reaction with a substrate. Positive, negative, and quantitative results are determined by detecting the color change in the reaction.
there are different types of the ELISA method used for GMO detection.
One type is known as “strip test” which uses lateral flow strips. And the results can be delivered in two to five minutes. Strip tests used when a rapid assessment to determine the presence or absence of GMOs is needed.
Another type of the ELISA test, the "plate test," provides indication of the quantity of the tested sample that is the GMO. The higher the amount of protein present, the more intense the color will be. The plate test can take two to four hours and is more laborious, and costly than the strip test.
this method is good because it a cheap and fast technique. however, ELISA tests have limitation in detecting GMOs in processed foods as heat processes denature the proteins, making detection of proteins difficult.

Figure 1. ELISA strip or "dipstick" tests can detect GMOs in grain and seed in three to five minutes.

Figure 2. ELISA "plate tests" can provide some quantitative assessment of the GMO present.

[Karthik Raman. (n.d.). Retrieved on 7th July 2010. Website: http://proline.physics.iisc.ernet.in/home/images/e/ee/Karthik-DNA-GMO.pdf]

[P. Markoulatos, N. Siafakas, A. Ppathoma, E. Nerantzis, B. Betzious, V. Dourtoglou & M. Moncany. (2004). Qualitative & Quantitive Detection of Protein & Genetically Modified Food. Retrieved on 7th July 2010, PP. 275-296, 2004]

[Eurofins Gene Scan. (2009, May 28). Genetically Modified Organisms (GMO) Technical Sheet. Retrieved from www.gmotesting.com/docs/GMO_Technical_Sheet.pdf]

[Thomison, P. R., & Loux, M. M. (2001). Commonly Used Methods for Detecting GMOs in Grain Crops. Retrieved July 10, 2010, from Ohio State University Extension fact Sheet, website: http://ohioline.osu.edu/agf-fact/0149.html]