Complementary use of 1H-NMR and multi-element IRMS in association with chemometric methods enables effective origin analysis of high quality cocoa (Theobroma cacao L.)

Stefan Bindereif1, Jan-Marcel Schubert2, Paul Rösch3, Stephan Schwarzinger3, Gerhard Gebauer1
1 BayCEER - Laboratory of Isotope Biogeochemistry, University of Bayreuth, 95447 Bayreuth, Germany
2 Original Beans, Keizersgracht 452, 1016 GD Amsterdam, The Netherlands
3 Department of Biopolymers, University of Bayreuth, 95447 Bayreuth, Germany

P 4.20 in BayCEERversity: Across scales, compartments & communities

Introduction

Within the market of fine cocoa (Theobroma cacao L.), quality and prices are mainly determined by geographical origin, making traceability indispensable. However, a solid scientific method for this purpose has not been developed yet. 

Material and Methods

Various cocoa samples from 20 countries have been profiled using, for the first time for cacao, a combination of multielement isotope-ratio mass spectrometry (IRMS) and nuclear magnetic resonance (NMR). 

Results

Dimensionality reduction of NMR data resulted in six sets of signals, which could be assigned to substances well-suited for discrimination purposes. Principal component analysis (PCA) as well as cross-validated partial least squares discriminant analysis (PLS-DA) of combined isotope data (δ13C, δ15N, δ18O, δ2H, %C, %N, %O, %H) and 1H-NMR fingerprints achieved improved separation with increased classification rates compared to classification with data of the isolated methods. Loading plots revealed complementary properties of the two analytical techniques, as IRMS contributed primarily to discrimination between countries, while NMR significantly contributed to the separation of regions and varieties. 

Conclusions

Combination of datasets from different analytical methods each providing a larger number of parameters, is proposed as a general tool to enhance both, accuracy and precision, in testing of foodstuffs for authenticity.

 



Keywords: IRMS, NMR, chemometrics, Theobroma cacao, food authenticity, origin analysis