You take a bite of your favorite chocolate, perhaps a bitter dark chocolate, or even a fruity ruby chocolate. What hits you next is a cascade of complex flavors, comprising of more than 600 different aroma components. Behind the delightful sensory experience, is a host of complex processes; from the growth of the cacao tree (Theobroma cacao), right through to the grinding of the cocoa beans.
Each factor contributes to the unique chemical make-up of a particular chocolate, which, as researchers at Towson University, Maryland, have demonstrated, can be used to track down its provenance. As the technique evolves, they hope that it could even pinpoint the exact farm from which a chocolate’s beans came from. This could offer a way to verify the various “fair-trade” or “organic farming” claims that may feature on a chocolate product's label.
“The project originated out of an idea I had for a lab in one of the courses I teach,” Dr Shannon Stitzel, the project's principal investigator, said in a statement. “The method we used to analyze chocolate bars from a grocery store worked well in the class, and the exercise piqued the students' curiosity. So, I started reaching out for more interesting samples and tweaking the technique.”
In Stitzel’s early experiments she used elemental analysis to determine the geographic location of chocolate samples. But to cut through the many processing steps of chocolate, Stitzel and her colleagues wanted to fine-tune their technique to find organic compounds in samples that would remain throughout the production procedures.
To do so, Stitzel dove back through the chocolate-making process to cocoa liquor. A combination of cocoa solids and cocoa butter, cocoa liquor is obtained after cocoa beans from the pods have been fermented, dried, roasted and then ground down. In addition to these post-harvest treatments, other factors impact upon the chemical composition of the liquor. These include the soil composition, weather and farming practices where the cocoa bean is grown, and even variations in naturally occurring yeast in the pods surrounding the beans.
After acquiring some samples of cocoa liquor from five different countries, Towson University undergraduate student Gabrielle Lembo set about uncovering their unique chemical signatures. By separating the compounds using liquid chromatography, Lembo could use mass spectrometry to find the particular make-up of each sample. Based on specific patterns of eight selected compounds (including caffeine, theobromine, and catechins), she then grouped together samples. This enabled her to successfully determine the country of origin in 95 percent of samples.
The research, due to be presented at the American Chemical Society Spring 2020 National Meeting and Expo, has now been published online. In their submission, the authors also noted that some of their current inaccuracies could reflect the different roasting temperatures of the beans; with those roasted at higher temperatures proving more problematic in the research.
In the future, as well as giving more thought to their inaccuracies, the team hopes to be able to identify the exact region within a country, even to the farm-level, from which cocoa beans originate. A useful piece of information when evaluating the claims on chocolate labels about their provenance.
However, if coffee is your vice, rather than chocolate, never fear, for the team is going to apply this method to look at the chemical signatures of various forms of fair-trade and organic coffee, too.