2018 | Oeser AR. Böhm Th. (Co-Autor):
Erlaubt – Verboten. Hygiene, Recht und Qualitätssicherung in Gemeinschaftsverpflegung und Gastronomie sicher umsetzen.
14. Auflage. 527 S. Behr’s Verlag Hamburg, ISBN 978-3-95468-584-4
Homogenized eggs obtained from feeding trials which contained residues of either furazolidone (FZ) or a mixture of 4 nitrofurans (FZ, furaltadone [FTD], nitrofurantoin [NFT] and nitrofurazone [NFZ] at ca. 40 µg/kg) were chemically or physically stabilized, packed and stored in order to find the best procedure for the preparation of stable reference material with residues of nitrofurans in eggs. The storage variables were different temperatures and packing materials, lyophilization, preservatives and irradiation with ϒ-rays. All samples were analysed 65 (69) weeks after storage started.
For the analysis of nitrofurans, an automated sample preparation system has been used. It was demonstrated that the system gained reproducible and accurate results even when used over a long period of time. Sample preparation was performed online with ASTED® (automated sequential trace enrichment of dialysates) before the four nitrofurans were quantitated by reserved phase HPLC and UV detection at 365 nm. ASTED® shows many advantages in comparison to traditional sample preparation techniques. Compounds of low molecular weight (e.g. veterinary drugs) are quickly separated by dialysis from macromolecular matrix substances (proteins, lipids etc.) in an aqueous environment and this avoiding the undesired use of organic solvents. Samples could be analysed in 24 hours with the help of ASTED® being about four times as many as a laboratory technician could analyse in an eight-hour working day using liquid/liquid partitioning and/or solid phase extraction procedures. However, the achievable limits of detection and of determination for the ASTED®-HPLC analysis were not fully satisfactory with 10 µg/kg (17 ng absolute) and 20 µg/kg (35ng absolute) respectively nitrofuran in egg. The analysis of the stored egg samples w under statistical control of a Shewhart quality control card by routineness running a set of check samples of standard and fortified egg samples.
Compared with samples before storage and those stored at -80°C as a reference no significant differences in nitrofuran content could be observed when the stored samples were kept in the original state or lyophilized at -20°C regardless of the packing material or the addition of preservatives (to avoid degradation during freezing and thawing). An influence of the packing material could be observed at higher temperatures. Lyophilized samples stored at +4°C showed the same results (within the limits of the analytical performance) as the -80°C reference when they were packed in glass or polypropylene tubes. Those that were sealed in polyethylene-polyamide bags showed a loss of 60-70 % of the original nitrofuran content. The superiority of glass could be seen with the lyophilized samples at +20°C. While all samples showed intense degradation of nitrofurans, this was 30-50% with glass-packed samples, 40-60% with polypropylene tubes and 100 % with the sealed bags. The amount of degradation was about identical between the four nitrofurans.
Storage of lyophilized samples at +50°C led to severe matrix interferences impairing the selectivity of the nitrofuran analysis. The irradiated (10 kGy) samples that were stored at +20°C showed a degradation of only 25 % at maximum. But since it was not determined whether this degradation was due to irradiation or storage at +20°C over 65-69 weeks, further investigations are necessary before irradiation can be considered as a means to gain room stable nitrofuran residues in lyophilised eggs. From the obtained experimental data it can be concluded that the most economic way to keep nitrofuran residues stable in a whole egg matrix is the storage of lyophilised material in glass at +4°C (protected from light).