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Evaluate using real-time PCR to detect soybean DNA in soy protein and flour products.

According to several European and American studies, up to 2% of adults and 8% of children may suffer from allergies that are derived from food. It is usually difficult to detect soy allergens. Soy products are so highly processed that using an enzyme-linked immunosorbent assay to detect the protein allergen can yield incorrect results.

So, scientists at Oklahoma State University evaluated how well the polymerase chain reaction (PCR) would do in detecting soy DNA, which could be used as the basis of confirming whether or not soy is in a food product. Although this test does not specifically target the allergen, it would determine the presence of soy for product labeling purposes. Their work yielded fairly good results.

The researchers evaluated whole soybeans, soybean protein concentrates, soybean protein isolates, soybean flour and soybean protein-fiber-lecithin products that had been obtained from commercial suppliers. From each product, they took a 100-mg sample. From these samples, they extracted DNA using a commercial extraction-isolation kit.

The extractions were performed in triplicate for each sample. The integrity of the DNA was visualized using agarose gels. The investigators performed real-time PCR with primers (short fragments of DNA) that were designed for the lectin gene in soybean. The extractions were diluted to 1000 nanograms of DNA.

To determine the detection limit of real-time PCR, the initial 1000 nanograms of material were serial-diluted 10-fold to 0.001 nanograms of DNA. Statistically speaking, the average coefficient of determination ([R.sup.2]) value was 0.991 for all of the samples. The scientists found that there were no significant differences in the detection limit for the replicated extractions. The detection limit using real-time PCR was repeatable for all products through the sixth dilution. This suggests a detection limit of 10 picograms. The quality of the DNA did not have any effect on the detection limit.

Subsequent research will evaluate this protocol using different food matrices, such as fat, protein and carbohydrate, to determine if detection limits can be maintained.

Further information. Christina M. DeWitt, Department of Animal Science, 125 Food and Agricultural Products Center, Oklahoma State University, Stillwater, OK 74078; phone: 405-744-3922; email:
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Publication:Emerging Food R&D Report
Date:Apr 1, 2010
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