A fundamental study of the application of cumin biomass in the recovery of Cu and Zn metal ion uptake from food and drinks is carried out at different pH's and at fixed ionic strength. The chemical characteristics of protein in cumin seeds were investigated. Results showed that cumin contains 18.25% crude protein, which includes 18 amino acids [F.H. Badr, EN. Georgiev, Food Chem. 38 (1990) 273]. The main reactive groups on protein cumin are amino and carboxylic groups of dicarboxylic amino acids, leading to a pH-dependent charge. Therefore, the cumin surface is considered as a heterogeneous system. To describe protonation behavior in a heterogeneous cumin biomass (cumin/0.1 M NaNO3) system, acid-base titrations have been performed with conductometric and potentiometric titration. Measurement of the reactivity of cumin surface in the adsorption of Cu and Zn metal ions and determination of metal binding at different pH's were also carried out. To solve broad and ill-defined titration curves, a simplified version of nonideal competitive analysis (NICA) by Plette et al. [Environ. Sci. Technol. 30 (1996) 1902] was applied. The results show that the sorption of the bivalent metal ions onto the whole surface cumin could be attributed to a monodentate binding to one site mainly carboxylic-type site. (C) 2003 Elsevier Inc. All rights reserved.