Using Proton NMR to Identify Fraudulent Cocoa Samples

The food industry has become a truly global trade, with foodstuffs routinely being transported thousands of miles before reaching the end consumer. This has made it increasingly difficult to definitively trace the origins of the food products reaching consumers and the ingredients used by food manufacturers.

Unscrupulous food traders are taking advantage of the increased complexity of the food market, intentionally deceiving customers to increase their profit margins. In such cases of food fraud, a valuable product will be bulked up with cheaper alternatives without this being indicated on the packaging. This had led to consumers paying high prices for sub-standard products.

For example, honey may be bulked up with corn or rice syrups. Alternatively, a product may be intentionally mislabeled as containing ingredients of a specific area or variety that is more desirable and so can be sold at a high price, for example, manuka honey.  

In order to combat such food fraud and protect consumers, spectroscopic technologies are successfully being used to verify the authenticity of honey and to validate the vintage and grape variety content of wines.

With the recent expansion in sales of specialist single-origin chocolate, fraudsters are now targeting this market and similar analytical methodologies are being explored for the verification of the origin of cocoa products.

Cocoa chocolate trufflesImage Credit: LightField Studios / Shutterstock.com

The cocoa market

Cocoa (Theobroma cacao L.) is the raw product used in the manufacture of chocolate. The quality and processing of the cocoa bean can significantly impact the quality and taste of the end-product.

The quality of cocoa is mainly determined by the location in which it is grown, but can also be affected by the way it is processed. Chocolate created from cocoa that has been cultivated in particular geographical regions can thus justify higher prices than chocolate containing cocoa from other regions.

The global demand for chocolate is higher than ever before, making cocoa one of the most economical tropical crops. In addition, single-origin and bean-to-bar concepts have become increasingly common marketing strategies used to justify the higher pricing of specialist chocolates1.

The majority of cocoa is sourced from small-scale, family-run plantations in West Africa (e.g. Ghana), and South America (e.g. Peru). The flavor of the harvested cocoa pods is enhanced by on-site fermentation and drying1.  

Proton NMR in the verification of cocoa authenticity

In one study, an analytical evaluation of cocoa samples using a range of spectroscopic techniques allowed cocoa to be classified according to the three major cocoa varieties (Forastero, Criollo and Trinitario) and to be linked to a particular region of cultivation3-6.

With numerous advances in proton nuclear magnetic resonance (1H NMR) technologies over recent years and the success of its application to authenticity screening of honey and wine, proton NMR is now being explored for determining the origin of cocoa.

Proton NMR simultaneously evaluates all the components in a sample, and so the spectral fingerprint will show that the compounds characteristic of the origin in question are present and that there are no additional unwanted ingredients. A comparison of the spectra from unverified samples with those of known samples provides a simple and rapid means of verifying authenticity.

This approach has successfully differentiated between cocoa samples of differing levels of fermentation, but it has proved more challenging to determine geographical origin using spectroscopic analysis. This is largely due to the changes in metabolite profile that occur during fermentation which obscure relevant information7.

A recent study profiled 48 cocoa samples from 20 countries using a combination of stable isotope-ratio mass spectrometry (IR-MS) and proton NMR8. Proton NMR spectra were obtained using a Bruker 400 MHz FoodScreener™ spectrometer equipped with a BBI probe head with z gradients.

Chemometric analysis of the IR-MS data and the proton NMR spectra resulted in good separation of the different cocoa samples and enabled better classification rates compared with the techniques used individually. No fractionation effects of fermentation were observed.

The two techniques complemented each other, each enabling different differentiations. IR-MS primarily facilitated discrimination between the country of origin, whereas proton NMR significantly aided the separation of cocoas of different varieties and cocoas cultivated in different regions within individual countries8.

These new data demonstrate that combining two analytical methods provides an effective tool for accurate authenticity testing of cocoa. Further research to verify these findings and refine the technique are thus warranted to develop a tool that has the potential to improve the accuracy and precision of cocoa authenticity testing.

References

  1. Beckett ST, et al. Beckett’s industrial chocolate manufacture and use. 2017 (5th ed.). New York: John Wiley & Sons.
  2. Saltini R, et al. Optimizing chocolate production through traceability: A review of the influence of farming practices on cocoa bean quality. Food Control 2013;29(1):167–187. erhttps://doi.org/10.1016/j.foodcont.2012.05.054.
  3. D’Souza RN, et al. Origin-based polyphenolic fingerprinting of Theobroma cacao in unfermented and fermented beans. Food Research International 2017;99:550–559. https://doi.org/10.1016/j.foodres.2017.06.007.
  4. Vargas Jentzsch P, et al. Distinction of Ecuadorian varieties of fermented cocoa beans using Raman spectroscopy. Food Chemistry 2016;211:274–280. https://doi.org/10.1016/j.foodchem.2016.05.017.
  5. Bertoldi D, et al. Multielemental fingerprinting and geographic traceability of Theobroma cacao beans and cocoa products. Food Control 2016;65:46–53. https://doi.org/10.1016/j.foodcont.2016.01.013.
  6. Perini M, et al. Stable isotope composition of cocoa beans of different geographical origin. Journal of Mass Spectrometry 2016;51(9):684–689. https://doi.org/10.1002/jms.3833.
  7. Caligiani A, et al. Application of 1H NMR for the characterisation of cocoa beans of different geographical origins and fermentation levels. Food Chemistry 2014;157:94–99. https://doi.org/10.1016/j.foodchem.2014.01.116.
  8. Bindereif S, et al. Complementary use of 1H NMR and multi-element IRMS in association with chemometrics enables effective origin analysis of cocoa beans (Theobroma cacao L.). Food Chemistry. 2019. https://www.sciencedirect.com/science/article/pii/S0308814619312105

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Last updated: Dec 18, 2019 at 9:09 AM

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