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 K(eqA) = ∝, behaving as the most stable and toxic species. At higher protein concentration (Phase C) it formed conjugate [DAB×SBP(gross)](conjugate), with K(eqC) = 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.