Team:UCSF/ALHS Project

Choosing the foods
We chose to use a variety of food, including fresh soy beans, tortilla chips, Fritos corn chips, papaya and a organic corn snack that claims it is made from an ancient variety of corn. We tested some foods that were labeled “non-GMO” and some that weren’t labeled at all.

Testing
We crushed up samples of each food up with a mortar and pestle, while adding small amounts of water to make a slurry. We then placed each sample into a microcentrifuge tube containing InstaGene, a chelating agent that helps to remove metal ions. We have to use this because it ensures that the PCR will be free of metal ions. After adding our samples to InstaGene, we shook the tubes and placed them into a 95°C water bath for 5 minutes. Afterwards, we centrifuged them for 5 minutes at the maximum speed, and then refrigerated them.

The next day, we removed the samples from the refrigerator and placed them on ice. We added all of the essential ingredients for PCR into a PCR tube, in addition to DNA from the samples we had centrifuged the previous day. After mixing the contents of the tube, we placed them into the thermal cycler. Finally, we used gel electrophoresis to see if fragments of DNA that would indicate that the sample is a GMO were present in the samples or not.

Lab Results:
To detect if the food products were GMOs, we analyzed the samples by gel electrophoresis and looked for the CaMV35S promoter and NOS terminator base on the base pair size of each gene. If a food was genetically modified, it showed a 203 bp band of CaMV35S promoter and a 225 bp band of NOS terminator. Whereas, a non-GMO food would not have these two bands. During the course of the lab we tested eight foods: Fritos brand corn chips, Hawaiian papaya, Inka Roasted Corn snack food, Santitas brand tortilla chips, raw soy beans, soy crisp snack chips (brand unknown), Bob’s Red Mill Cornmeal (labeled “all natural”) and Bob’s Red Mill Cornbread Mix. Four of these eight foods proved to contain the CaMV35S promoter and the NOS terminator: Fritos, papaya, tortilla chips, and the “all natural” cornmeal. The students were surprised to find no proof of genetic modification in fresh soy beans or soy crisp snack chips, even though some sources claim that 91% of the U.S. soybean crop is genetically modified. However, in testing the soy foods, the CaMV35S and NOS terminator bands did not appear. Interestingly enough, the cornbread mix did not show evidence of genetic modification while the same-brand cornmeal did. Please see the full data represented in the chart below: