Cooking beef at moderate temperatures results in the production of numerous heterocyclic amines, several of which have been found to be mutagenic towards Salmonella typhimurium TA98. It was the purpose of this work to separate, purify, and characterize some of these products. The sources of mutagenic activity for these experiments were commerical beef extract (intended for use in bacteriological media), food-grade beef extract, and fried ground beef. After extraction into methylene chloride, the samples were fractionated on Adsorbosil-5 silica gel columns. Three major peaks of activity were found in the effluent from the (bacteriological-grade) beef extract (designated I, II, and III). In contrast, only two peaks were obtained from food-grade beef extract and fried ground beef (designated, respectively, I and III, and I and IV). The peaks were further purified by Sephadex LH-20 column chromatography and high-performance liquid chromatography on Ultrasil-NH2 and Supelcosil LC-18 columns. The purified samples were then analyzed by high- and low-resolution mass spectrometry. The component in Peak I (from all three sources) was found to have a molecular ion at m/z 213 with an empirical formula of C11H11N5 and a fragmentation pattern consistent with the molecular structure of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline. The component in Peak II (found only in bacteriological-grade beef extract) was tentatively identified as 2-amino-3,4-dimethylimidazo[4,5-f]quinoline by its predominant molecular ion at m/z 212 and a fragment of M—15. The component in Peak III (from both beef extracts but not in fried ground beef) was found to have a mass spectrum virtually indistinguishable from 2-amino-3-methylimidazo[4,5-f] quinoline. The only mutagen common to both beef extracts and fried ground beef was 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline. 2-Amino-3-methylimidazo[4,5-f]quinoline was not found in the fried ground beef extract. However, the fried ground beef extract did contain another more polar mutagen (Peak IV) which has not yet been identified.
This research was supported in part by the College of Agricultural and Life Sciences, University of Wisconsin-Madison (CALS Research Division Project 2640); the University of Wisconsin-Madison Graduate School; the Wisconsin Agricultural Experiment Station; the United States Department of Agriculture; the University of Wisconsin-Madison Food Research Institute; and USPHS Research Grant R01-CA29618, awarded by the National Cancer Institute, Department of Health and Human Services.