Formation of mutagens by heating foods and model systems.

Abstract

We have demonstrated that the pyrolysis products of amino acids and proteins in model systems are mutagenic. The mutagenic principles in the pyrolyzates of amino acids have been isolated and identified by Sugimura et al. We have isolated and identified amino-a-carbolines from pyrolyzed soybean globulin as mutagens. The yield of mutagens by the heating of food constituents is changed by the heating method. Effects of heating methods on the yield of amino-a-carbolines were studied in a series of experiments, and the results are shown in this paper. Additionally, it has been shown that by the heating of creatinesugar mixtures imidazoquinoline or quinoxaline mutagens are formed.We demonstrated previously that the pyrolysis products of amino acids and proteins in model systems are mutagenic (1,2). The mutagenic principles in the pyrolyzates of amino acids have been isolated and identified by Sugimura et al. (3,4). We have isolated and identified amino-a-carbolines from pyrolyzed soybean globulin as mutagens (5). The yield of mutagens by the heating of food constituents is changed by the heating method. Formation of Amino-oL-carbolines It was supposed that amino-ot-carbolines (I) and amino-y-carbolines as well as Trp-P-1 or Trp-P-2 would be formed from the tryptophan moiety of protein. Therefore, a relationship between tryptophan content in the protein and the pyrolytic formation of mutagens was studied (6). Zein, gluten, globulin, casein, and albumin as well as chicken meat and horse mackerel were pyrolyzed at 5500C and the yield of mutagens was determined. The content of tryptophan in these materials was determined by an amino acid analyzer. The yield of amino-a-carboline correlated positively with the content of tryptophan in the protein, and it was 60 to 850 times that of Trp-P-2.Yield of amino-ca-carboline and Trp-P-2 per gram of tryptophan in the protein was calculated (Table 1). The yield of amino-ot-carboline per gram of tryptophan in the protein was higher than that of free tryptophan, especially for albumin and chicken meat. Although proteins and proteinaceous materials tested in this experiment showed appreciably higher yield of amino-a-carboline than that expected from the tryptophan content, *Central Research Institute, The Japan Tobacco & Salt Public Corporation, 6-2 Umegaoka, Midori-ku, Yokohama 227 Japan. the yield of Trp-P-2 per gram of tryptophan in the protein was lower than that of free tryptophan and indicated little difference among the proteins tested. The reason for the formation of higher amounts of amino-acarboline than expected from the tryptophan contents remains obscure.The effect of heating temperature on the yield of amino-a-carboline was determined using albumin. Amino-a-carboline was formed when albumin was heated to a temperature of 200°C, and the concentration increased with increasing temperature. The maximum yield of the carboline was obtained at 600 to 700°C, and the ratio of amino-a-carboline to mutagenic activity of whole heated product was approximately constant among the heati...