Maize is the staple food of the Mexican population, and it is highly susceptible to contamination by aflatoxins (B1, B2, G1 and G2). Aflatoxins are produced by the fungi Aspergillus flavus, A. parasiticus and A. nomius, they are very toxic secondary metabolites, where aflatoxin B1 (AFB1), is the most important one for its pathogenic effects, such as mutagenicity, teratogenicity and carcinogenicity mainly for the liver. Lime is used in the thermo-alkaline treatment applied to maize, and alters the properties of the grain. Several studies have stated that aflatoxins are not dangerous because they are inactivated by lime treatment, that they are diminished with the washing and that alkali produces a chemical modification by opening the lactone ring of the AFB1. When the lactone ring of AFB1 opens, the fluorescence is lost and the toxin can not be detected. However with an acid pH, the lactone ring closes and the original molecule is restored. Our results showed that lime treatment decreased both the AFB1 initial concentration and its toxicity. We applied a Digestion Model in vitro to study the mutagenicity of tortillas, with saliva, pepsin and pancreatin, samples were analyzed by Ames test with T98 Salmonella typhymurium and the AFB1 concentration by HPLC. Lime treatment decreased of the initial concentration of AFB1 in maize tortilla but the AFB1 is mainly disguised and it is recovered with the acids of the digestion. Lime treatment opens the lactone ring of the AFB1, camouflages its fluorescence, and forms a salt of calcium, from the AFB1 attached to lime, and this mycotoxin cannot be purified with the chemical procedure. However, in contact with acid pH, the lime salt is destroyed and the AFB1 fluorescence is restored and newly detected. When the tortillas were digested “in vitro” by saliva, gastric and pancreatic juices, done with solutions of pepsin and pancreatin, we found a higher concentration of AFB1, with the action of both saliva and pancreatin, and similar results where obtained with saliva + pepsin +pancreatin. The pH of the enzimatic solutions, is very important for the chemical and the biological activities of AFB1, because with a pH of 7.0, 7.5 and 5.0, we obtained the highest values of both activities, while with a pH of 1.2 and 1.8 the AFB1 concentration was reduced and we did not observed a mutagenic effect. Some of the analized controls were saliva, enzymatic solutions made with pepsin and pancreatin, solvents, salts, acids and alkalis alone and without AFB1. There was no mutagenic effect with them at all the analyzed pH concentrations. This results suggest an added effect of the enzymatic solutions and the neutral pH on the mutagenic effect of AFB1. We conclude that the enzymatic activities of the saliva (pH 7.0) and pancreatin (pH 7.5), are very important in the recovery of the fluorescence and mutagenic activities of AFB1. With saliva, pancreatin and the 3 enzymes together, there were more revertant colonies due to AFB1, in Ames test , than in the controls. Pepsin (pH 1.2) inhibited the mutagenic effect of AFB1.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)