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Laccase enzymes are polyphenol oxidase that catalyze the oxidation of wide range of phenolic components including phenols, polyphenols, aromatic amines and non-phenolic substitution with molecular oxygen as electron acceptor. So these enzymes have biotechnological application such as wastewater treatment system, bioremediation of soil pollution and etc. Result from previous studies showed an increase in thermal stability of bacterial laccase from Bacillus sp. HR03 using site directed mutagenesis and the effect of E188 residue on the surface regions at the interface between domain 1 and 2 in stability was confirmed. The aim of the present work was to investigate the effect of this amino acid substitution on enzyme activity in the presence of dimethyl sulfoxide and dimethylformamide as organic solvents. Compression of kinetic parameters including Kcat / Km ، ∆∆G‡, C50 showed significant increases in the mutant enzyme than wild type enzyme, that industrial application of the enzyme will be easy.

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Celiac disease is the most common disease caused by gluten consumption and the only way to prevent it is to use gluten-free foods. The aim of this study was to optimization the formulation of gluten-free bread based on quinoa flour, laccase enzyme, and xanthan gum. For this purpose, the sensory properties and texture of bread under the influence of independent variables including quinoa flour (0-50%), xanthan gum (0-0.5%), and laccase enzyme (0-2 units of enzyme activity per gram of flour (U/g) were evaluated using the response level method based on the central composite design. Then some qualitative characteristics of gluten-free bread sample in optimal conditions were compared with the control sample (gluten-free bread containing rice and corn flours without quinoa flour, laccase enzyme, and xanthan gum) for 7 days of storage. The results showed that quinoa flour and laccase enzyme had a significant effect on sensory properties including crust color, porosity, taste, aroma, firmness, and overall acceptibility (p<0.05) of breads. While the effect of quadratic level of gum on overall acceptibility as well as the interaction of laccase enzyme and xanthan gum on bread firmness was significant (p<0.05). The optimal bread formulation consisted of 40% quinoa flour, 0.46% xanthan gum, and 2 U/g laccase enzyme. Comparison of the gluten-free optimal sample with the control gluten-free sample showed that the enthalpy and peak temperature of the control bread was higher than the optimal bread, which indicates more staleness. In terms of textural properties and sensory evaluation, the optimal sample was significantly better than the control sample. However, in terms of L* color indice, the control sample showed higher values (p<0.05).