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Abstract
Fried beef and commercial beef extracts contain Ames/Salmonella frameshift mutagens that form at relatively low temperatures (100–200°C). To investigate the types of natural components in beef muscle that give rise to frameshift mutagenic activity, we previously devised a model boiling system and demonstrated that all of the Salmonella TA1538 activity is formed from H2O‐soluble, < 500 molecular wt compounds that are present in round steak supernatant fractions (S1 and S2). S2 is derived from S1, the soluble fraction of homogenized beef, by a brief 30 min boil and centrifugation. We now report that proteolysis of beef S1 with papain, trypsin, or chymotrypsin (± carboxypeptidase A) increases the mutagenic activity of boiled S2 by 1.8–4.5 fold over the baseline range of 90–100 TA1538 revertants/108 bacteria/g dry beef/14 h at pH 4.0. Sequential treatment of beef S1 with chymotrypsin followed by carboxypeptidase A is the most efficient mutagen enhancing digestion (415 revertants/g dry beef or 7.7 revertants/mg of S2 soluble protein). Fourteen h boiled, proteolytic digests of round steak insoluble‐protein fraction (R1), soybean protein, bovine serum albumin, and bovine α‐lactalbumin contain much less TA1538 activity/mg of soluble protein than beef S2 (0.01–1.5 versus 7.4 revertants/108 bacteria). For comparison, S2 fractions prepared from chicken (light meat), chicken (dark meat), pork chops, turkey (light meat), beef liver, fish (sole), and whole eggs yield 89, 60, 71, 67, 58, 36, and < 1 TA1538 revertants/108 bacteria/g of initial dry wt. Despite their low TA1538 activity yields, S2‐like fractions from proteolyzed beef R1, soybean protein, and the two pure albumins, and S2 fractions from sole and eggs were comparable to our standard beef S1 or S2 in their amino acid compositions. Collectively, these mutagenicity and amino acid composition data indicate that select amino acids and/or small peptides plus some essential non‐amino acid compounds are the mutagen precursors in beef muscle.
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