Semicarbazide is non-specific as a marker metabolite to reveal nitrofurazone abuse as it can form under Hofmann conditions

Abstract

Detecting illegal nitrofurazone treatment of food-producing animals has been undermined by the reliance on semicarbazide as a marker metabolite for analysis because, during processing, semicarbazide forms in a variety of foods not exposed to nitrofurazone by previously unexplained pathways. In this study, formation of semicarbazide was examined under dairy product processing conditions. Hypochlorite dosed into milk on an industrial scale, at concentrations extreme for unintentional residues, produced monochloramine, but, without pH adjustment, hypochlorite alone did not generate semicarbazide. Dosed hypochlorite and peroxyacetic acid each generated low ng g⁻¹ levels of semicarbazide in milk (and whey) only when used in conjunction with localised high pH conditions, which can occur during both anion exchange and neutralisation. Dosed hydroxyurea generated semicarbazide at any pH, with greatest levels formed at high pH. Detecting nitrofurazone abuse can be better accomplished by analysis either for nitrofurazone itself or for the marker metabolite 5-nitro-2-furaldehyde, rather than semicarbazide.

Keywords:

• semicarbazide
• nitrofurazone
• 5-nitro-2-furaldehyde
• Hofmann reaction
• urea
• hypochlorite
• peroxyacetic acid
• chlorourea
• hydroxyurea
• dairy
• ion exchange

Acknowledgements

The author thanks Vanessa Green, Mike Howell and Mark Pritchard for advice on commercial whey demineralisation, Colin Knight for operating the pilot plant spray-drier, and Russell Richardson for ammonium analysis. The quality of the professional service provided by Moira Lymburn (AgriQuality, Lower Hutt) for semicarbazide analysis is also gratefully acknowledged.