Chocolate ‘fingerprints’ could confirm label claims

The flavour and aroma of a fine chocolate emerge from its ecology, in addition to its processing. However, it has been suggested that information of chocolate labels and packaging might not always be entirely truthful or accurate. Presenting their results through the American Chemical Society (ACS) SciMeetings online platform, researchers have developed a method for determining the origin of chocolate by looking at its chemical ‘fingerprint’.

“The project originated out of an idea I had for a lab in one of the courses I teach,” said Shannon Stitzel, Ph.D., the project’s principal investigator. “The method we used to analyse 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.”

Many factors can affect a chocolate’s flavour and contribute to its unique chemical make-up. The process of making chocolate begins with the pods of the cacao tree, and the genes of the tree the pods are harvested from, as well as the environment the tree is grown in, can affect the composition of the final product.

Processing steps can also change a chocolate’s complex chemistry. Generally, after cocoa beans obtained from the pods have been fermented, dried and roasted, they are ground into a paste, called cocoa liquor, which contains cocoa solids and cocoa butter. Sugar and other ingredients are added to the liquor to make chocolate. Any of these steps could be varied slightly by the company performing them, leading to differences in chocolate composition. Even more variation between chocolates from different regions can come from naturally occurring yeast in the pods that surround the beans, which can affect the fermentation process, thereby influencing the flavour compounds in chocolate.

The researchers said that being able to track a chocolate bar to a specific farm could help verify that the product is ‘fair trade’ or ‘organic,’ as its label might suggest, or that it has not been adulterated along the way with inferior ingredients.

Stitzel acquired single-source samples of cocoa liquor from all over the world. Her undergraduate student, Gabrielle Lembo, used liquid chromatography (LC) to separate the cocoa liquor compounds from various samples and mass spectrometry (MS) to identify their chemical signatures. Lembo’s results reportedly showed that LC-MS is a robust analysis technique. She said that compounds, such as caffeine, theobromine and catechins, are detected in different patterns that make up a signature fingerprint, and that this indicates provenance and cannot easily be finagled by nefarious producers.

Stitzel stated that eventually their method could be used to help map out the expected flavour profiles of a chocolate, given its chemical signature, and that it would be interesting to first determine the fingerprint of a cocoa bean, then gather fingerprints with each consecutive processing step to see how they change. For now, her students are expanding the application of the analysis method by looking at the chemical signatures of various forms of fair-trade and organic coffee.