Na vele jaren van onderzoek en debat, voerde de Europese Comissie op 1 januari 2019 een nieuwe wet in die de cadmium (Cd) concentratie in chocoladeproducten beperkt. De aanwezigheid van dit zwaar metaal in chocolade kan grotendeels toegeschreven worden aan de de origine van de cacaobonen. Dit maakt dat de exportpositie van veel Zuid- Amerikaanse landen zwaar onder vuur komt te staan.
In het kader van deze nieuwe regulering trachtten we een mogelijke strategie te ontwikkelen om Cd in cacaobonen te verlagen. De focus van dit onderzoek lag op de natuurlijke fermentatie van cacaobonen. Deze na-oogst behandeling is immers cruciaal in de ontwikkeling van het o zo karakteristieke cacao-aroma waar we allen zo dol op zijn. Door de beperkte kennis omtrent Cd in cacao, werd eerst de spreiding van Cd in ongefermenteerde cacao onderzocht. Later werd dan ook de mate waarin Cd zich (mogelijks) herverdeeld tijdens de fermentatie onderzocht.
We concludeerden dat Cd zich voornamelijk opstapelt in de zaadhuid (testa) van de cacaoboon. De Cd concentratie in het binnenste deel, de cacao nib, was daarentegen tot wel 50 % lager. Tijdens fermentatie nam dit verschil in concentratie nog verder toe: er was dus met andere woorden een duidelijke uitwaartse migratie van Cd. Deze herverdeling is mogelijks toe te schrijven aan veranderingen in pH van de verschillende weefsels. Zo zagen we dat Cd meer werd gemobilizeerd indien de nib pH beneden een bepaalde waarde (rond pH 5) daalde. Deze afname in pH werd hoodzakelijk veroorzaakt door een inwaartse beweging van kleine organische zuren zoals azijnzuur en melkzuur. Uitgaande van deze observaties, zou een wasbehandeling met pH verlagende substanties dus mogelijks kunnen leiden tot een lagere nib Cd op het einde van de fermentatie. Aangezien enkel nibs worden gebruikt voor verdere verwerking, volgt hieruit dat de finale Cd concentratie in chocolade dus verlaagd zou kunnen worden door gebruik te maken van deze strategie.
Of we nu door deze regulering met z’n allen minder chocolade moeten gaan eten is nog maar de vraag. Zo mag een volwassen man van 70 kg bijvoorbeeld tot 1,75 kg melkchocolade of 220 g donkere chocolade per week eten alvorens hij nadelige effecten van de geassocieerde Cd inname zal ervaren. Wie toch verleidt wordt door de intoxische effecten van chocolade en dergelijke hoeveelheden wekelijks consumeert, zal zich dus eerder zorgen moeten maken om hart –en vaatziekten alvorens in te zitten met de toxiciteit van Cd.
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