Production of γ-aminobutyric acid (GABA) was investigated using rice-bran extract for effective utilization of agricultural resources. In the experiments using L-glutamic acid as substrate and rice bran extract as an additive including enzyme, the GABA production reaction stoichiometrically proceeded. The optimum conditions of pH and temperature for GABA production were at pH 5.5 and 30~40°C. The kinetic parameters of rice-bran extract using L-glutamic acid as a substrate were also evaluated by a mathematical model that considered the material balances of L-glutamic acid and GABA, and reaction rate expressed by Michaelis-Menten’s equation. The model successfully explained the concentration profiles of experimental data.

The objective of this study was to evaluate the role of anatase impurities in sediments and the NaCl concentrations in the leaching solutions during the Cd(II) leaching from artificially contaminated sediments. It was found that the leaching of Cd(II) increased with increasing NaCl concentrations but this trend was less significant for the sediments containing higher amount of anatase. Based on the modeling analyses considering surface complexation and ion exchange reactions, the observed experimental results were explained by the difference between kaolinite and anatase in the Cd(II) adsorption mechanisms. At pH 5.9, which was the pH during the preparation of artificially contaminated sediments, kaolinite absorbs Cd(II) mainly via outer-sphere complex formation and that is why the absorbed Cd(II) was easily desorbed by the Na⁺ containing in the leaching solutions. On the other hand, the dominant Cd(II) adsorption mechanism for anatase was inner-sphere complex formation which was not hindered by the presence of NaCl. These experimental and modeling analyses results consistently showed that the content of anatase in sediments was one of the factors controlling the leaching level of Cd(II) from sediments when exposed to leaching solutions with high NaCl concentration.