Screening Food Products For The Presence Biology Essay


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Genetically modifying organisms began in the 1970s and is now becoming a prominent method in food production Devonchik, 2001. The process of GMO has allowed scientists to create crops that are pest resistance, drought resistant and resistant to other environmental stresses (Devonchik, 2001). When these benefits are considered why shouldn't every nation use GMO as a main source of food? It does seem like the ideal solution in solving poverty and in growing crops in harsh conditions. The issue with GMO is the lack of knowledge about the consequences it may induce; scientists are suggesting that there may be health risks involved (Otero & Pechlaner, 2009). Many European nations believe that genetically modifying organisms is too perilous, and that it may have dire consequences, such as genetically modified genes spreading out of control and destroying natural species (Devonchik, 2001).

As GMO may be considered unsafe at the present by some nations, procedures for testing food for Genetic modification have been developed (Regional Review- Federal Reserve Bank of Boston, 2004). Most developed countries are cautious of GMO and have regulations for their introduction into the marketplace (Regional Review- Federal Reserve Bank of Boston, 2004). Labelling of foods derived from genetically modified crops is occurring in most countries with a standard that would permit only 1% trace amounts of GMOs in food products that claimed they were GMO free (Cocheo, 2000). This is opposed to developing countries that do not employ testing procedures for foods that may have been genetically modified (Regional Review- Federal Reserve Bank of Boston, 2004).

Methods for testing food for GMO have been developed and one of the most sensitive and specific methods is using the polymerase chain reaction (PCR) (Koenders, 2010). PCR is generally the first choice in analytical laboratories testing for GMO (Jensen et al, 2003). The most important factor affecting the specificity of PCR is the target sequence motif choice (Jensen et al, 2003). The target sequence is generally a terminator, a promoter, a gene or a junction between two of these elements (Jensen et al, 2003). Using the PCR method exact inserted sequences can be detected (Koenders, 2010).

The aim of this study to determine whether store bought foods that had no labeling stating they were GMO free or claimed to be GMO free contained genetically modified genes. This was done using the PCR method.

The PCR method was used to test foods for the presence of GMO traces. The aim of this experiment was to determine if any genetically modified genes were present in a range of store bought food that either claimed to be GMO free or did not state if GMO was present in the food. As labelling in mandatory in Australia for foods containing GMO these foods should come up negative for GMO content. Control foods that were labelled as containing GMO were used to compare to the experimental non- GMO foods. The specific genetically modified sequences that were tested for were the 35S promoter of the cauliflower mosaic virus (CaMV 35S) and the terminator of the nopaline synthase (T-nos) gene of Agrobacterium tumefaciens (Koenders, 2010). The promoter CaMV 35S and the terminator T-Nos are the main sequences that are found in GMOs (Jensen et al, 2003). The CaMV 35s is used so frequently because it is a strong and constitutive promoter (Jensen et al, 2003). The function of the T-nos is to signal the termination of the herbicide and insect tolerant gene expression (Jensen et al, 2003). The Photosystem II gene is used as a control for comparison.

The experimental foods (ones that were labelled non-GMO) that were tested for GMO content were flour, corn chips, veggie fillets, Doritos, crispbread, veggie sausage, mung beans and tofu. A control sample known to contain GMO and one known to not contained any GMO were also tested.

It is expected that the experimental food samples will test negative for GM content but positive for the Photosystem II gene and the GMO controls will contain either the CaMV 35S promoter or the nos terminator.


See appendix for lab notes (Koenders, 2010).

Deviations from the lab manual include


7. Used vortex instead of "shaking well".


8. Run the agarose 200V for 20 minutes instead of 100V for 30 minutes


The results from the experiments show that there were no GMO primers in any of the experimental foods tested. The only positive result for the GMO primers came from one of the GMO control samples. The photosystem II gene was found in the following foods: mung bean, plain flour, tofu, veggie sausage, the positive control, corn chips (non gmo and gmo), crisp bread and the veggie fillet. Some of the food samples indicated in table one by an 'error' label did not produce adequate results.

In this experiment the photosystem II gene was determined to be present when the band length was approximately 450-500bp (455bp indicates its presence), and the GMO primers were roughly found at band length 200bp, with CaMV 35S being 203bp and nos being 225bp usually.

Table one: Results of food samples tested for presence of the plant and GMO primers using the PCR method. Symbol '+' indicating a positive result for the gene and '-' indicating no result and 'error' indicating an error in the test process.

Test Food

Plant Primer

GMO Primer

Flour (Non GMO)



Corn Chips (GMO)



Corn Chips (Non GMO)



Veggie Fillet (Non GMO)



Doritos (Non GMO)



Crispbread (Non GMO)






Veggie Sausage (GMO)



Mung Beans (Non GMO)



Tofu (Non GMO)




Testing foods for the presence of the CaMV 35S promoter DNA sequence and the nos terminator DNA sequence to determine if they contain GMO is a common practise, as either or both of these DNA sequences occur in 86% of all GM crops approved around the world (The TAG Working Group on GM Food Labelling, 2003). Our results showed that there was no CaMV 35S or nos present in any of the food samples except for the control GMO sample, this control was at band length 200bp which as indicated in the results we interpreted to mean GMO presence. All food samples that used the PMM primer tested positive for the photosystem II gene. It was expected that all the foods labelled non-GMO or without any labelling (the experimental) would not contain CaMV 35S or nos as this indicates that they do not contain GMO. It was also expected that all food samples using the PMM primer would test positive for the photosystem II gene as this gene is common in most plants and the samples were plant based. If the photosystem II gene does not show up in the tests, the results are invalid as the Photosystem II gene is used as a control.

A study of GMO content in foods undertaken in Egypt using the PCR method showed that out of 24 food samples tested 3 products (canola seeds, Diamant potato tubers and squash seeds) gave positive results when tested for the 35S promoter (Oraby et al, 2005). However they also found that the same 3 products gave negative results when tested with the NOS 3 primers (Oraby et al, 2005). The positive and negative results, for the same food products, further confirm the conclusion reached by Wurz et al. suggesting that more than one primer is required to detect a GM product (Wurz et al, 1999). This is why in our study two primers were used to determine GMO content.

The Australian and New Zealand food standards code came into force in December of 2001 (The TAG Working Group on GM Food Labelling, 2003). It requires any food, food ingredient or processing aid produced using gene technology and containing novel DNA or novel protein to be labeled as 'genetically modified'(The TAG Working Group on GM Food Labelling, 2003). The standard allows 1% of unintentional presence of GM food or ingredient in a final food product; this standard was also put into place by the European Union in Europe (Cocheo, 2000). Studies done in Australia using the PCR method under the GMO standard indicated that GM products were found in many of the foods tested even though they did not have labels present (The TAG Working Group on GM Food Labelling, 2003). The concentration of GMO DNA present was however under the 1% limit and therefore falls into the category of unintentional presence of GM products (The TAG Working Group on GM Food Labelling, 2003). Many of the businesses who had their foods tested were unaware that there was a standard for GM content (The TAG Working Group on GM Food Labelling, 2003). The experimental food samples that were tested in our experiment did not have labels stating that they had GM ingredients present therefore it was expected that there would be no positive results for GMO genes. The results we obtained show that none of the experimental food samples contained GMO.

The invention of PCR saw a new era come about in the field of molecular biology with its wide range of purposes (Morisset et al, 2008). Currently, using PCR for GMO diagnostics is still the most frequently used technology as it the most sensitive and versatile method (Morisset et al, 2008). The PCR method does however have some drawbacks; the cost of PCR testing is relatively expensive with one study reporting that each food sample cost around $664 dollars (The TAG Working Group on GM Food Labelling, 2003). The process of PCR testing is a long one with repeated precision temperature cycling needed (Morisset et al, 2008). Alternate methods (LAMB and PCR/LDR) for detecting GMOs have already been discovered and trialled (Morisset et al, 2008). The results are promising and some flaws in the PCR method do not occur in these new methods. For example the LDR method is less expensive and does not need repeated precision temperature cycling (Morisset et al, 2008). The LAMB method has also tested to be speciWcity to target DNA in a real-time detection along with high sensitivity (Morisset et al, 2008). These methods may one day replace the PCR method, however today PCR despite its limitations is the most prominent method used for detecting GMOs in a range of different food samples.


The experiment that we undertook using the PCR method indicates that food labelling in Perth is working. The food labelled non-GMO or foods without labelling produced results that designated them GMO free. This results was expected and means that the foods we tested are complying too the Australian and New Zealand food standard code. As our range of test samples was small it would be interesting to see if a larger test including more foods would produce different results.

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