Sample extraction and preparation of
filtrate were conducted
according to ISO methodsdetails
of the procedures are presented in Table 2. Briefly, aliquots 1–10 gof the samples were
treated with tetraborate sodium (for plant foods and meat
products, only), Carrez solutions including potassium hexacyano-
ferrate (II) trihydrate (Carrez I) and zinc acetate solution (Carrez II);to obtain a clear liquid sample, extraction was followed by
filtration through
filter paper (Whatman, grade 41, Ashless,
12.5 cm). For dairy products, sample extractions were also
centrifuged at 1200g for 15 min and the supernatants were
removed for ultra-filtration.