Agriculture Reference
In-Depth Information
No data has been published regarding the accumulation or depletion of
AMOZ, AHD or SEM in porcine tissues. However, a study has suggested that
depletion of AOZ and AMOZ residues from broiler chicken muscle and liver
was similar to that seen for AOZ in porcine tissues [51] have also shown that
SEM residues accumulate at higher concentrations and have a longer half-life
than other nitrofuran metabolites in tissues of broilers hatched from breeding
chickens which received nitrofuran medicated feed [52].
The stability of metabolites during the storage and cooking of meat was
demonstrated [53]. Eight months storage did not have a significant effect on
the residual concentration of nitrofurans in incurred pig muscle and liver
samples. The authors observed that between 67% and 100% of the residues
remained present in the tissue after cooking, frying, grilling, roasting and
microwaving. Another study demonstrated that AOZ in egg was stable up to
(at least) 12 months during storage at 4°C, and that 78% of AOZ occurs in the
yolk as opposed to albumin [44]. Recently it was also observed that 50% of
total SEM residues in egg were found in the shell, which may be significant if
an eggshell product reaches the consumer [54].
Although the metabolism of nitrofurans is not well documented, a
suggested mechanism is through cleavage of the nitrofuran ring, leaving the
specific tail group covalently bound to tissue [55]. In vivo , these metabolites
can be released by natural stomach acids [43]. This fact is taken into
consideration in the isolation of metabolites for residue analysis as early
mentioned. Due to the higher stability and longer residence time (between 4
and 9 days half-life time) of the bound metabolites, their detection is still
possible when concentrations of the parent drugs have fallen below their
detection limits.
Is now perceptible that the nitrofuran metabolites accumulate in retinal
tissue to very high concentrations. In pigs (and depending on the nitrofuran
concerned), retina concentrations after withdrawal of medication range from
0.1 mg kg -1 (AHD) to 13.8 mg kg -1 (AMOZ). These concentrations, which are
several orders of magnitude higher than the corresponding concentrations in
more conventional matrices (liver, kidney, muscle, etc.), are sufficiently high
for laboratories equipped only with HPLC-UV should be able to detect
nitrofuran use in food animals for prolonged periods after cessation of
treatment.
In adition, nitrofurans accumulate in eggs in the form of the parent drug. It
is a quirk of the analytical procedure, developed as part of FoodBRAND
project, that any parent drug present in a sample is measured as its
corresponding metabolite. If an egg containing furazolidone (parent drug) is
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