‘From soil to chocolate bar’: identifying critical steps in the journey of cadmium in a Colombian cacao plantation

Abstract

Regulation of maximum levels of cadmium in chocolate is an issue for cacao exportation from many parts of Latin America, including Colombia. These limits are related to the final product, but buyers often request maximum levels of Cd in the beans. However, to date, there is neither a clear understanding of the relationship between the specified levels of Cd in chocolate and cocoa derivatives and levels in harvested beans or soil nor of the effect of post-harvest processes on the levels of Cd in the final product. To address this, the fate of Cd concentration from soil to chocolate bar was followed in a single farm in Santander district, Colombia. The concentration of Cd in soils was measured using ICP-OES and correlated with soil pH, soil organic matter (SOM), and the use of P-based fertilisers. Cd concentrations were also measured in unfermented seeds, fermented and dried beans, shell, nibs, and chocolate. SOM (2.93–3.78%), soil pH (4.7–4.9), soil P concentration (120–132 mg kg⁻¹) affect Cd availability. However, it is still unclear whether Cd concentration of P-based fertilisers (3–30 mg kg⁻¹) is important or not. While post-harvest treatments did not affect the Cd concentration of beans (4.17 ± 0.8 mg kg⁻¹ on average), the removal of the shell (6.57 mg kg⁻¹) from the nibs (3.28 mg kg⁻¹), as well as the percentage of cocoa mass used contributes to a reduction in Cd concentration in the chocolate bar (1.60 mg kg⁻¹). This study provides clear indications on where research into mitigation measures should be focussed, as well as indicating the importance of carrying out analyses for Cd in the nib or cacao mass, rather than the whole bean, reducing Cd concentration by up to 40%.

Graphical Abstract

Keywords:

• Soil
• fertilizers
• post-harvest
• fermentation
• nibs
• shells
• chocolate
• mitigation

Acknowledgements

We gratefully acknowledge the generous assistance provided by unknown reviewers of this manuscript. The samples were collected according to the Colombian Resolution No. 1466 of 3 December 2014, by which AGROSAVIA has collected permission to perform biological diversity sampling for non-commercial and scientific research purposes. We thank Karin Chatelain for the chocolate sample production in the Chocolate Factory Laboratory of the Institute of Food and Beverage Innovation of the University of Applied Sciences (Zürich, Switzerland). We also would like to acknowledge Dr. Eduardo Chávez from ESPOL University in Guayaquil, Ecuador, for Cd determination in chocolate samples and Iván Chacón-Garzón for the design drawings of the fermenter system. The experiments in Peru were carried out in the processing plant of the Agrarian Cooperative Norandino in collaboration with Fredy Yovera Espinoza.

Author contributions

DB conceived and designed the experiments; performed the experiments; analysed and interpreted the data; contributed reagents, materials, analysis tools, or data; drawn figures; wrote the paper and performed the final edition. MS performed the experiments; analysed and interpreted the data; drawn figures; wrote the paper and assisted the final edition. JR conceived and designed the experiments; performed the experiments; analysed and interpreted the data; analysis tools or data; wrote the paper and collaborate in the final edition. SE conceived and designed the experiments; performed the experiments; analysed and interpreted the data; contributed reagents, materials, analysis tools, or data; drawn figures; wrote the paper and assisted in the final edition. RA analysed and interpreted data from Peru to compare with the available data from Colombia and assisted in the final edition. GR analysed and interpreted data from Trinidad and Tobago to compare with data from Colombia. Both RA and GR also contributed to the final discussion and conclusions of the study.

Disclosure statement

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Data availability statement

The datasets generated during and/or analysed during the current study are not publicly available. However, related data at the municipality may be available upon request to the corresponding author.

Additional information

Funding

This work was supported by the Corporación Colombiana de Investigación Agropecuaria AGROSAVIA, through grants No. 1000664 and 1001134 as part of the internal projects of the research agenda entitled ‘Cd in cacao and the strategies to tackle it’ and ‘Cacao in post-harvest processes’. Moreover, this project was supported by Fontagro through the project: Multi-agency cocoa platform for Latin America and the Caribbean ‘Cocoa 2030–2050’ with the grant ATN/RF-17235-RG. The study in Peru was funded by the USAID through the USDA-led program ‘Cacao seguro’. This study was also supported by the Colombian Ministry of Agriculture and Rural Development (MADR).