This paper proposes a mechanism to explain the trace levels of natural semicarbazide occasionally observed in foods. The analytical derivative of semicarbazide, 2-nitrobenzaldehyde semicarbazone, is often measured as a metabolite marker to detect the widely banned antibiotic nitrofurazone. However, this marker is not specific as semicarbazide may be present in foods for several reasons other than exposure to nitrofurazone. In some cases, an entirely natural origin of semicarbazide is suspected, although up until now there was no explanation about how semicarbazide could occur naturally. In this work, semicarbazide is proposed as being generated from natural food compounds via an azine intermediate. Hydrazine, in the form of azines or hydrazones, may be generated in dilute aqueous solution from the natural food compounds ammonia, hydrogen peroxide and acetone, following known oxidation chemistry. When this mixture was prepared in the presence of ureas such as allantoin, urea, biuret or hydroxyurea, and then analysed by the standard method for the determination of semicarbazide, 2-nitrobenzaldehyde semicarbazone was detected. 2-Nitrobenzaldehyde aldazine was also found, and it may be a general marker for azines in foods. This proposal, that azine formation is central to semicarbazide development, provides a convergence of the published mechanisms for semicarbazide. The reaction starts with hydrogen peroxide, peracetic acid, atmospheric oxygen or hypochlorite; generates hydrazine either by an oxaziridine intermediate or via the chlorination of ammonia; and then either route may converge on azine formation, followed by reaction with a urea compound. Additionally, carbamate ion may speculatively generate semicarbazide by reaction with hydrazine, which might be a significant route in the case of the hypochlorite treatment of foods or food contact surfaces. Significantly, detection of 2-nitrobenzaldehyde semicarbazone may be somewhat artefactual because semicarbazide can form during the acid conditions of analysis, which can free hydrazine in the presence of urea compounds.

本文提出了一种机制来解释偶尔在食物中观察到的天然氨基脲的痕量水平。氨基脲的分析衍生物2-硝基苯甲醛氨基脲经常被作为代谢物标记物进行检测，以检测被广泛禁止的抗生素硝基呋喃酮。但是，该标志物不是特异性的，因为除了暴露于呋喃酮以外，还有几种原因可导致食物中存在氨基脲。在某些情况下，怀疑存在氨基脲的完全天然来源，尽管到目前为止，尚无关于氨基脲如何天然存在的解释。在这项工作中，建议将氨基脲从天然食品化合物中通过一种嗪中间体生成。肼或hydr的形式的肼可在稀水溶液中由天然食品化合物氨生成，按照已知的氧化化学方法制备过氧化氢和丙酮。当在尿素如尿囊素，尿素，缩二脲或羟基脲的存在下制备该混合物，然后通过标准方法分析氨基脲时，检测到2-硝基苯甲醛半脲。还发现了2-硝基苯甲醛醛嗪，它可能是食品中嗪的通用标记。这项提议认为，嗪的形成对氨基脲的发展至关重要，这一提议使已公布的氨基脲的作用机理趋于一致。反应从过氧化氢，过氧乙酸，大气中的氧气或次氯酸盐开始；通过恶唑烷中间体或氨氯化生成肼。然后任一种途径都可以收敛于形成嗪，然后与脲化合物反应。此外，氨基甲酸酯离子可能通过与肼反应而推测地产生氨基脲，这在食品或食品接触表面的次氯酸盐处理中可能是重要的途径。重要的是，检测2-硝基苯甲醛半脲可能是人为的，因为在酸性条件下会形成氨基脲，在尿素化合物存在的情况下会释放出肼。