Alginate-gelatin mixed gel was applied to immobilized laccase for decolorization of some synthetic dyes including crystal violet. The immobilization procedure was accomplished by adding alginate to a gelatin solution containing the enzyme and the subsequent dropwise addition of the mixture into a stirred CaCl2 solution. The obtained data showed that both immobilized and free enzymes acted optimally at 50°C for removal of crystal violet, but the entrapped enzyme showed higher thermal stability compared to the free enzyme. The immobilized enzyme represented optimum decolorization at pH 8. Reusability of the entrapped laccase was also studied and the results showed that ca. 85% activity was retained after five successive cycles. The best removal condition was applied for decolorization of seven other synthetic dyes. Results showed that the maximum and minimum dye removal was related to amido black 10B and eosin, respectively. Introduction While traditional methods in chemical processes have improved in the last decades, extensive attention has been paid to alternative techniques that utilize enzymes involving excellent characteristics, such as high activity, selectivity, and specificity. In addition, enzymes action at mild conditions of pH, pressure, and temperature proposes them as candidates for suitable catalysts in industries where low cost, energy savings, and simplicity are important [1, 2]. However, despite these advantages, some practical problems restrict their use, such as the high-cost isolation and purification process and instability in organic media and high temperatures. To overcome these limitations, several methods have been suggested and the most important of which are immobilization techniques [3, 4]. Enzyme entrapment uses natural and synthetic polymers, such as agarose, agar, and gelatin, through thermoreversal polymerization alginate, polyvinyl acetate, acrylic acid, and β-carrageenan by ionotropic gelation [5]. Gelatin consists of proteins and peptides produced by the denaturation of collagen, which breaks down into smaller fragments. Due to its unique physical properties, such as a melting point close to physiological temperature, gelatin is used in a variety of applications, especially in the food and pharmaceutical industries [6]. Gelatin immobilization methods have been developed for entrapment of microbial cells and enzymes, especially when the enzyme is placed in a whole cell. While the gelation process is reversible with temperature and displays no efficient immobilization, other than at 30–35°C, some methods have been
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