Determination of the Provenance of Cocoa by Soil Protolith Ages and Assessment of Anthropogenic Lead Contamination by Pb/Nd and Lead Isotope Ratios

作者：Manton William I^*

来源：Journal of Agricultural and Food Chemistry, 2010, 58(2): 713-721.

DOI：10.1021/jf9029207

• Cocoa beans
• chocolate products
• lanthanides
• lead
• lead isotopes
• lead contamination
• soil protolith age

The Pb contents of chocolate and the products it flavors are among the highest of all commonly consumed substances. Others have shown that this Pb is acquired by cocoa beans after harvesting and is concentrated in their shells, portions of which are ground up with the cotyledons during processing. It is shown here that the shells also contain the lanthanides Nd and Sm, which they appear to take up more slowly than Pb when dried on bare soil. Consideration of Pb/Nd ratios, model Sm-Nd ages and the isotope ratios of Pb and Sr indicates that, in the absence of contamination, the relationship between Pb and Nd in shells is y = 13.1 x(-0.383), where x is the Nd concentration in mu g/kg and y is the Pb/Nd ratio. For cocoa powders, the relationship is y = 114x(-0.988). Samples that plot above these curves are probably contaminated. Model ages indicate where the cocoa of cocoa powders is grown, and these same considerations point to African samples being uncontaminated but samples from Asia containing 50% anthropogenic Pb of Australian origin. No measurable Pb contamination occurs during the transport of beans and the manufacture of chocolate.

• 出版日期2010-1-27