In Vitro Adsorption of Aluminum by an Edible Biopolymer Poly(γ-glutamic acid) Yesudoss Christu Rajan, † Baskaran Stephen Inbaraj, † and Bing Huei Chen* ,†,‡ † Department of Food Science and ‡ Graduate Institute of Medicine, Fu Jen University, Taipei 242, Taiwan ABSTRACT: Accumulation of aluminum in human has been reported to be associated with dementia, Parkinson’s disease, and Alzheimer’s disease. The objectives of this study were to evaluate an edible biopolymer poly(γ-glutamic acid) (γ-PGA) for aluminum removal efficiency under in vitro conditions as affected by pH, contact time, aluminum concentration, temperature, ionic strength, and essential metals in both aqueous aluminum solution and simulated gastrointestinal fluid (GIF). A low aluminum adsorption occurred at pH 1.5-2.5, followed by a maximum adsorption at pH 3.0-4.0 and precipitating thereafter as aluminum hydroxide at pH > 4. Adsorption was extremely fast with 81-96% of total adsorption being attained within 1 min, reaching equilibrium in 5-10 min. Kinetic data at low (10 mg/L) and high (50 mg/L) concentrations were well described by pseudo-first-order and pseudo-second-order models, respectively. Equilibrium adsorption isotherms at different temperatures were precisely fitted by both Langmuir and Redlich-Peterson models with the maximum adsorption capacities at 25, 37, and 50 °C being 35.85, 38.68, and 44.23 mg/g, respectively. Thermodynamic calculations suggested endothermic and spontaneous nature of aluminum adsorption by γ-PGA with increased randomness at the solid/solution interface. Variation in ionic strengths did not alter the adsorption capacity, however, the incorporation of essential metals significantly reduced the aluminum adsorption by following the order copper > iron > zinc > calcium > potassium. Compared to aqueous solution, the aluminum adsorption from simulated GIF was high at all studied pH (1-4) with Langmuir monolayer adsorption capacity being 49.43 mg/ g at 37 °C and pH 4. The outcome of this study suggests that γ-PGA could be used as a safe detoxifying agent for aluminum. KEYWORDS: poly(γ-glutamic acid), aluminum, detoxification, gastrointestinal pH, kinetics, isotherms, essential metals ■ INTRODUCTION Aluminum is one of the most common and abundant metallic elements in the Earth’s crust. 1 Until a decade ago aluminum was regarded as an inert and insoluble mineral that does not pose any threat to human health. Consequently, aluminum containing agents have been used in many applications including food, drinking water, and medicine. 2-4 Moreover, acid rain in recent years has transformed the insoluble aluminum-containing minerals into a more soluble form resulting in accumulation of aluminum in food through drinking water sources. 3,4 Though aluminum compounds are currently used in industrial and pharmaceutical sectors as cosmetics, food additives, and household products, the major route of exposure of aluminum to human is through food. 3,4 Unprocessed foods typically contribute less than 5 mg of Al/kg, however, the use of aluminum-based foils, bowls, vessels, trays, and pans in the presence of acids and salts may elevate the level of aluminum in food. 3 For a 60 kg adult, the mean dietary exposure from food and water was estimated to range from 1.6 to 13 mg of Al/day, which corresponded to 0.2-2.3 mg/kg body weight per week. 3 Nevertheless, the tolerable weekly aluminum intake recommended by EFSA is only 1 mg of aluminum/kg body weight/week. 3 Moreover, several studies have implicated that aluminum accumulation can cause neurotoxicity leading to increased risk of neurological and bone disorders such as Alzheimer’s disease, Parkinson’s disease, dementia, and osteomalacia. 3-6 Thus, it is important to explore new therapeutic methods to minimize aluminum accumulation in human body. Theoretically, aluminum mainly exists as a soluble species Al[(H 2 O) 6 ] 3+ at pH ≤ 4, but at pH > 4, it can be precipitated as Al(OH) 3 through transient formation of Al(OH) 2+ and Al(OH) 2 + . 3,7 Accordingly, at physiological pH (5.5-7.4), aluminum should precipitate, preventing its absorption through the gastrointestinal tract. However, several in vivo studies have demonstrated increased accumulation of aluminum during simultaneous administration of aluminum hydroxide and fruit juices or organic acids (citric, ascorbic, and glutamic acids). 7-10 This is because various dietary ligands in conjugation with gastric juice solubilize the aluminum cations, resulting in the equilibrium formation of a soluble complex of aluminum for enhanced absorption and bioavailability. 8,9 Chelation therapy is one of the most common methods used for treatment of patients with metal poisoning. Several chelators such as desferrioxamine and feralex have been found beneficial for reduction of tissue accumulation of aluminum in human. 11,12 Nevertheless, these chelators may cause potential side effects including kidney overload, mineral deficiency, and cardiac arrest. 13 Therefore, it is essential to develop potential and safe detoxifying agents for treatment of aluminum poisoning. In this study, an edible and biodegradable biopolymer poly(γ-glutamic acid) (γ-PGA) was evaluated as a safe detoxifying agent for aluminum in a batch mode under in vitro conditions. The γ-PGA consists of repetitive glutamic acid Received: March 12, 2014 Revised: May 2, 2014 Accepted: May 5, 2014 Published: May 5, 2014 Article pubs.acs.org/JAFC © 2014 American Chemical Society 4803 dx.doi.org/10.1021/jf5011484 | J. Agric. Food Chem. 2014, 62, 4803-4811