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Cadmium migration from nib to testa during cacao fermentation is driven by nib acidification

Abstract:

Previous work has shown that cacao nib cadmium (Cd) concentrations decrease during fermentation, but only when reaching sufficiently low nib pH. In this work, lab-scale experiments (5 kg units) with lactic and acetic acid amendments were ineffective at reducing the total nib Cd concentration. In contrast, the water-extractable fraction of the nib Cd concentration clearly increased when the pH was decreased. When single pod derived beans were embedded inside a full-scale fermentation box to monitor the effect of the fermentation effect with high precision, nib Cd concentrations decreased by a factor 1.25 (P-value <0.05) after four days of fermentation. Visualisation of the mobile Cd gradient within beans with LA-ICP-MS (using imprints of transversal cuts exposed to a metal binding gel) revealed that fermentation enhances the Cd mobility in the nibs.