Semicarbazide formation during processing and storage of dairy protein ingredients

Semicarbazide is often used as a marker metabolite for detection of illegal nitrofurazone use in agricultural products, but is not a reliable marker metabolite for analysis of nitrofurazone abuse dairy products because it can also be formed during processing and storage. To further investigate that the semicarbazide found in dairy protein ingredients is formed during processing, rather than from nitrofurazone abuse, a series of studies were conducted. Almost 500 commercial dairy protein ingredients were manufactured and analysed, and semicarbazide was detected in 22.4% of samples. Semicarbazide was detected in <10% of caseinates and >20% of all whey protein concentrate (WPC) samples analysed. Notable differences were observed between different WPC subcategories in terms of the frequency of detection and levels of semicarbazide. Higher semicarbazide levels were observed in WPC with a higher protein content or that were fat-rich. Importantly, semicarbazide was not detected in either the raw materials or intermediate products during dairy protein ingredient production but were only found in final, dried, dairy protein ingredients. This indicates that semicarbazide formation likely occurs during (spray-)drying or during storage after manufacture. Higher semicarbazide levels were found at higher storage temperature and higher water activity of the ingredients. No other nitrofuran metabolites were detected in any of the samples. The investigations presented in this report confirm previous reports that semicarbazide found in dairy ingredients is not present in raw materials but formed during processing and storage.