Study of nickel content in Ni-rich food products in Slovenia

In the present study, total nickel (Ni) concentration was determined in selected food products in Slovenia by inductively coupled plasma mass spectrometry (ICP-MS) after microwave assisted digestion of samples. The accuracy of the analytical procedure was checked by the determination of nickel in SRM 2976 NIST Mussel tissue and SRM 1548a NIST Typical diet standard reference materials. Results confirmed that soya products (yoghurt and tofu), cacao and cacao products (dark and milk chocolates) and hazel nuts are important sources of dietary Ni. The content of Ni in different teas infusions was too low to significantly contribute to Ni daily intake. Cooking of acidic foodstuffs in stainless steel kitchenware leached Ni in concentrations similar to those in teas. Micro-ultrafiltration (MWCO 3000 Da) of cacao cooked in water or milk revealed that Ni in these drinks is present in the form of low molecular mass (LMM) species and that milk proteins are not able to compete for Ni in the presence of LMM-Ni binding ligands.