Contents - Faperta

Detection and Monitoring of Food and Food Products 473
towards the detector. During this process, the molecules are separated based on mass and
charge ratio. This technique has been used successfully in genotyping of single nucleotide
polymorphism (SNP) of genes, and can also be used for detection of genetically modifi ed
food (Miraglia et al., 2004).
Surface Plasmon Resonance
Surface plasmon resonance (SPR) uses thin-layered metal fi lms (plasmon) on a sensor chip,
usually coated with gold, to which the molecules (protein, DNA, or oligonucleotides) are
bound. The surface is rinsed with a fl uid that contains a binding partner to the surface
attached molecules. The interaction between the molecules is studied by polarized light,
which is refl ected from the plasmon surface. If the molecules from the fl uid and the chip
bind to each other, the refl ected light intensity is reduced, and the size of change in the
surface plasmon resonance signal is directly proportional to the mass. This system has
been used for detection of herbicide-resistant soybean by immobilizing biotinylated PCR
products of the target oligonucleotides on the chip and hybridizing them with respective
probes (Feriotto et al., 2002). This approach of detecting genetically modifi ed foods needs
to be evaluated further. Electro chemiluminescence PCR (ECL-PCR) combined with the
hybridization (probes labeled with biotin and TBR) technique has also been used for
detecting genetically modifi ed food (Liu et al., 2004). This method can rapidly detect genetically
modifi ed food with high sensitivity, over a wide range.
At the moment, only PCR offers a general screening for transgenic crops, and detection
of particular “events.” Phenotypic characterization and immunoassays detect particular
traits that may be present in several transgenic crops (e.g., the Cry1a protein and genes
conferring insect resistance are present in a number of maize cultivars).
Monitoring of Genetically Modified Food and Food Labeling
The current policies on authorization and labeling of products derived from genetically
modifi ed plants in different countries are not clear, and often hampers international trade.
Therefore, there is a need to harmonize these regulations globally. Harmonization of
national requirements for labeling of genetically modifi ed products will lead to increase in
transparency in international trade in food and food products. Harmonized data requirements
are essential for internationally accepted analytical methods and reference materials
and implementing current and future regulations governing genetically modifi ed food.
At the moment, the detection methods are DNA based in Europe, while the United States
follows a protein-based system, and the two approaches may give different results depending
on the matrix under analysis.
Despite lack of regulations to provide information on food and food products derived
from genetically modifi ed plants, many products carry positive or negative labels with
regard to genetic modifi cation. A maize product not labeled as genetically modifi ed has
been found with ELISA to contain the transgene product (Urbanek Karlowska et al., 2003).
In another study involving 58 soybean and maize products in the food chain in South Africa,
44 tested positive for the presence of genetically modifi ed plants. Of the 20 products labeled
as genetically modifi ed, only 14 tested positive, suggesting the need for effective
regulations for production and labeling of food derived from genetically modifi ed plants