Food forensics: using mass spectrometry to detect foodborne protein contaminants as exemplified by Shiga toxin variants and prion strains

Authors: Silva, Christopher - Chris

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2018
Publication Date: 6/2/2018
Citation: Silva, C.J. 2018. Food forensics: using mass spectrometry to detect foodborne protein contaminants as exemplified by Shiga toxin variants and prion strains. Journal of Agricultural and Food Chemistry. 66(32):8435-8450. https://doi.org/10.1021/acs.jafc.8b01517.
DOI: https://doi.org/10.1021/acs.jafc.8b01517

Interpretive Summary: The study of contaminants in food or food forensics is probably as old as civilization itself. Ancient Egyptians wrote of (~1127 BC) the efforts of a female scribe named Henuttawi to ensure that the correct vessel was used to measure the wheat used to feed the Pharaoh’s workers. In the 21st century, our food sources come from all over the world and not just along the Nile. Our food can also be highly processed, which introduces the possibility for adulteration, alteration, or contamination at any of the many steps from the source to the fork. A scientific instrument called a mass spectrometer accurately measures the weight or mass of molecules. It has been used to identify the characteristic molecules of food contaminants. Mass spectrometers can filter molecules by their molecular weights using a technique called multiple reaction monitoring (MRM). MRM has been used to analyze very large molecules called Shiga toxins and infectious proteins called prions. The Shiga toxins are responsible for the most serious forms of E. coli caused foodborne illnesses. Prions are infectious proteins whose shape converts a normal cellular prion protein into the prion shape to cause an infection. The five identical B subunits that, along with a toxic A subunit, make up a Shiga toxin were used to detect it. Prion detection was based on isolation of prions using their characteristic properties. Both Shiga toxins and prions were rendered harmless by the steps required for an MRM-based analysis. These examples illustrate how the same mass spectrometer can be used to analyze very large protein toxins, prions, and much smaller molecules, thereby ensuring that our food is safe to eat.

Technical Abstract: Food forensicists need a variety of tools to detect the many possible food contaminants. As a result of its analytical flexibility, mass spectrometry is one of those tools. Use of the multiple reaction monitoring (MRM) method expands its use to quantitation as well as detection of infectious proteins (prions) and protein toxins, such as Shiga toxins. The sample processing steps inactivate prions and Shiga toxins; the proteins are digested with proteases to yield peptides suitable for MRM-based analysis. Prions are detected by their distinct physicochemical properties and differential covalent modification. Shiga toxin analysis is based on detecting peptides derived from the five identical binding B subunits comprising the toxin. 15N-labeled internal standards are prepared from cloned proteins. These examples illustrate the power of MRM, in that the same instrument can be used to safely detect and quantitate protein toxins, prions, and small molecules that might contaminate our food.