Aminoazo dye-protein-adduct enhances inhibitory effect on digestibility and damages to Gastro-Duodenal-Hepatic axis

4-Dimethylaminoazobenzene (DAB, methyl yellow, or butter yellow), a human carcinogen, has been banned for use in foods since 1988. In 2014, DAB adulteration in Tofu occurred in Taiwan. We hypothesize that DAB can form [DAB•SBP]adduct adduct with soybean protein (SBP) which could damage Gastro-Duodenal-Hepatic axis. Sprague-Dawley rats gavage fed [DAB•SBP]adduct adduct revealed severely reduced body weight and damaged duodenum, liver, hepatic mitochondria, and spleen. Hepatic levels of glutathione and ATP were severely reduced. Serum GOT and GPT were substantially elevated. Analysis by the adsorption isotherm clearly revealed DAB formed very stable [DAB•SBP]adduct adduct at 1:1 molar ration (Phase A). The equilibrium constant of this colloidal adduct [DAB•SBP]adduct was KeqA = ∝, behaving as the most stable and toxic species. At higher protein concentration (Phase C) it formed conjugate [DAB×SBPgross]conjugate, with KeqC = 3.23×10−2 mg/mL, implicating a moderately strong adsorption. The in vitro pepsin digestibility test showed apparently reduced digestibility by 27% (by Ninhydrin assay) or 8% (by Bradford assay). Conclusively, this is the first report indicating that [DAB•SBP]adduct potentially is capable to damage the Gastro-Duodenal-Hepatic axis.