Dried distillers grains with solubles (DDGS) are the dried remains of the production of ethanol from corn by fermentation and typically is sold as a high protein livestock feed that increases efficiency and lowers the risk of subacute acidosis in beef cattle (link to Wikipedia page).
The way in which antibiotics end up in DDGS is during the fermentation of corn for ethanol production when a mixture of antibiotics is added to prevent the growth of bacteria that overgrows the yeast, and, thus, reduces the amount of ethanol produced. But, the U.S. FDA regulates drugs and ingredients used in animal feed production (link to USFDA page), and has raised concern about the amount of antibiotics in DDGS.
By the way, distillers grain (DG) is not only the second largest category of processed feed in the U.S., but also nearly 25% of U.S. DGs are exported to countries, such as China, Mexico, and Canada.
Application Note 1055, Determination of Virginiamycin, Erythromycin, and Penicillin in Dried Distillers Grains with Solubles (link to downloadable PDF) describes an HPLC method with charged aerosol detection developed in our Sunnyvale Applications Lab in California for determining the four most commonly used antibiotics in ethanol fermentation–virginiamycin (two forms), erythromycin, and penicillin–at low concentrations in DDGS.
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This is a challenging analytical problem as these four antibiotics are very chemically different, making separation a challenge, and lack good chromophores, making detection a challenge. The additional challenge is that these three compounds are in a complex sample matrix.
The method includes multi-step sample preparation for the DDGS, followed by separation of the four antibiotics on one of our HPLC protein and peptide columns (Thermo Scientific Acclaim 300 C18 column) using a volatile mobile phase. They were then detected using our latest charged aerosol detector (Corona ultra RS Charged Aerosol Detector). Our rapid separation HPLC system (Thermo Scientific Dionex UltiMate 3000 RSLC system) was used in the experiment. All four antibiotics were separated within 15 mins with the column cleanup and equilibration taking an additional 10 mins.
The method is easily reproducible and should be of interest to ethanol producers, companies that purchase DDGS from ethanol producers, animal feed companies, and regulatory bodies interested in assessing the antibiotic content of DDGS.
Let us know if you have any questions on this application; we look forward to hearing from you!