If you buy extra virgin olive oil, caveat emptor. Olive oil has been an avenue for corruption for hundreds and perhaps even thousands of years. Some extra virgin olive oil in studies was found to not only not be extra virgin, it wasn't even olive oil.

'Premium' chocolate has the same issue. Anyone can put Premium on a label and the only way to really know was to buy it and taste it - and if you bought it, you compounded the problem.

Writing in the Journal of Agricultural and Food Chemistry, researchers say they have developed a method to authenticate the varietal purity and origin of cacao beans, the source of chocolate's main ingredient, cocoa. 

They used cacao genomics to identify a single-nucleotide polymorphisms (SNPs) - a small set of DNA markers - that make up unique fingerprints of different cacao species. The technique works on single cacao beans and can be scaled up to handle large samples quickly. "To our knowledge, this is the first authentication study in cacao using molecular markers," the researchers state. 

Dapeng Zhang and colleagues note that lower-quality cacao beans often get mixed in with premium varieties on their way to becoming chocolate bars, truffles, sauces and liqueurs. But the stakes for policing the chocolate industry are high. It's a multi-billion dollar global enterprise, and in some places, it's as much art as business.

There's also a conservation angle to knowing whether products are truly what confectioners claim them to be. The ability to authenticate premium and rare varieties would encourage growers to maintain cacao biodiversity rather than depend on the most abundant and easiest to grow trees.

Researchers had already found ways to verify through genetic testing the authenticity of many other crops, including cereals, fruits, olives, tea and coffee, but those methods weren't suitable for cacao beans. Zhang's team have now addressed this challenge.

Citation: Wanping Fang, Lyndel W. Meinhardt, Sue Mischke, Cláudia M. Bellato, Lambert Motilal, and Dapeng Zhang, 'Accurate Determination of Genetic Identity for a Single Cacao Bean, Using Molecular Markers with a Nanofluidic System, Ensures Cocoa Authentication', J. Agric. Food Chem., 2014, 62 (2), pp 481–487 December 19, 2013 DOI: 10.1021/jf404402v. Source: American Chemical Society