Effect of pH on Binding of Mutagenic Heterocyclic Amines by the Natural Biopolymer Poly(γ-glutamic acid)

• Published in: Journal of agricultural and food chemistry Vol. 54; no. 17; pp. 6452 - 6459
• Main Authors: Inbaraj, B. Stephen, Chiu, C. P, Chiu, Y. T, Ho, G. H, Yang, J, Chen, B. H
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 23.08.2006
• Subjects: Adsorption; Biological and medical sciences; Carbolines - chemistry; Carbolines - metabolism; Chemical Phenomena; Chemistry, Physical; Chromatography, High Pressure Liquid; Food industries; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Mutagens - metabolism; Polyglutamic Acid - analogs & derivatives; Polyglutamic Acid - metabolism; Quinolines - chemistry; Quinolines - metabolism; Quinoxalines - chemistry; Quinoxalines - metabolism; Binding; Amine; Adsorption; heterocyclic amines; Biopolymer; multimolecular adsorption; pH; Scatchard plot; isotherms; Natural; poly(y-glutamic acid); Langmuir isotherm
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf061300o

Poly(γ-glutamic acid) (γ-PGA), a nontoxic and biodegradable macropolymer, was evaluated for its efficiency in binding three mutagenic heterocyclic amines (HAs), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-p-2), as affected by pH in a batch mode. The maximum HA sorption was attained for pH 3−7 and decreased sharply for pH less than 3. Binding isotherms obtained at pH 2.5 and 5.5 showed different isotherm shapes that belong to S and L types, respectively. The isotherm data at pH 2.5 were well described by a linear form of the Langmuir equation, while at pH 5.5 it showed two distinct curves, which were precisely fitted as multiple Langmuir curves. The deviation of linearity in Scatchard plot proved the multisite HA sorption. The Brunauer−Emmett−Teller equation also fitted better to isotherm data at pH 5.5, suggesting a multisite sorption caused by multimolecular HA layers on γ-PGA. High HA sorption levels of 1250, 667, and 1429 mg/g at pH 2.5 and 1429, 909, and 1667 mg/g at pH 5.5 were observed for MeIQ, 4,8-DiMeIQx, and Trp-p-2, respectively. Among the HAs studied, the sorption capacity correlated directly with hydrophobicity of HAs and inversely with the number of methyl groups in HA molecules. The plausible binding mechanism of HAs on γ-PGA may include a combination of hydrophobic, hydrogen-bonding, ionic, and dipole−dipole interactions. Keywords: Adsorption; poly(γ-glutamic acid); heterocyclic amines; isotherms; Langmuir isotherm; Scatchard plot; multimolecular adsorption