Using Genetics to Identify Contamination in High-Quality Cacao

How can you be sure that high-end candy bar contains only the best chocolate?  The answer, of course, is genetics.

A new paper (pdf:  Accurate Determination of Genetic Identity for a Single Cocoa Bean Ensures Cocoa Authentication) out this month in the Journal of Agricultural and Food Chemistry demonstrates the use of genetic markers to identify contamination of premium cacao beans with lower quality beans.  The scientists used a panel of 48 genetic markers (SNPs, microsatellites, and the like) to determine if cacao bean samples were only premium beans (from the cacao variety called Fortunato No. 4) or if there was also low-quality beans in the mix.  A brief summary appears here.

This study joins various others that have looked at food authenticity.  News stories abound about supermarkets and restaurants substituting cheaper products without telling the customers.  Growing up in Florida, the rumor was always that the scallops we were eating were, in reality, shark meat.

That story may be apocryphal, but since then other real cases have surfaced.  I’ve read about students examining the meat from the local grocery store using DNA genotyping who found that the stores had changed the names of the fishes they were selling.  A more recent news story talked about restaurants serving sliced pig anus instead of calamari (a writeup appears here).  Too boot, in taste tests, people could not tell the difference between these two meats.

This paper on cacao beans would be a good read for discussing the use of genetic technologies to investigate food fraud.  Please note that the analysis is heavy on the computation, including some clustering analysis, that can get bogged down in the details.  I recommend simplifying the data to make it more approachable to students.  For the cluster maps, ask students what it means when some points cluster together and the others are farther away.

Other thought questions to ask:

  • To what other industries would you want to apply genetic testing of products?  Why?
  • In what industries would it be difficult to use genetic testing?  An example could be purebred dog breeds which, since they are all the same species, may require many more genetic markers to map out specific differences.
  • How would you make a news story out of this article?  What are the important points that consumers and the public should know?
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