Exploiting subtle differences in a key meat protein, the addition of just 1% of horse into a beef burger or of beef into lamb mince is now easy to spot. Not only that, the technique gives an estimate of how much unlabelled meat is illegally concealed in the product.
The red colour of meat is due to a protein called myoglobin. Proteins are made up of ‘building blocks’ called amino acids, and, for example, the myoglobin of beef differs from that of horse by 18 amino acids. This means that if the beef and horse proteins are broken up in the same way, we can detect these small differences in amino acid composition by measuring the respective mass of protein fragments within a sample.
This is the basis of the new test. Protein extracted from a meat sample is chemically chopped into fragments, called peptides, using an enzyme. The peptide soup is fed into a mass spectrometer that is tuned to measure the masses of only a handful of selected peptides. If a burger contains only beef then only beef peptides will appear. But if a little horse meat has been slipped in then some horse peptides will show up too. In this fraudulent case the relative hit rate of the horse and beef peptides give an estimate of how much horse has been added. The entire procedure takes around two hours.
The IFR work, led by Dr Kate Kemsley, appears in the September issue of the Journal of Visualized Experiments as a free downloadable video clip showing how the experiment is done. JoVE is the world’s first peer review scientific video journal. This research was described in more detail in a paper in journal Analytical Chemistry, and was funded by the Biotechnology and Biological Sciences Research Council.
Though so far demonstrated using raw meat from just four species, the team have also shown that key marker peptides persist in supermarket products, including for lamb in ready-curry and for beef in canned corned beef. So the team is confident they can reveal meat adulteration in cooked retail products, of key interest to consumers and producers alike. The IFR group have teamed up with researchers in Stuttgart and Gdansk to extend this technique into other more complicated food products based on a suite of protein targets.
Gunning, Y., Watson, A. D., Rigby, N. M., Philo, M., Peazer, J. K., Kemsley, E. K. Species Determination and Quantitation in Mixtures Using MRM Mass Spectrometry of Peptides Applied to Meat Authentication. J. Vis. Exp. (115), e54420, doi:10.3791/54420 (2016).
Meat Authentication via Multiple Reaction Monitoring Mass Spectrometry of Myoglobin Peptides, Andrew D. Watson, Yvonne Gunning, Neil M. Rigby, Mark Philo, and E. Kate Kemsley, Analytical Chemistry 87 (20), 10315-10322 doi: 10.1021/acs.analchem.5b02318