Thermal Destabilization of Rhizomucor miehei Rennet with Aldehyde Dextran Sulfate: Purification, Bioconjugation and Milk-Clotting Activities.

High thermal stability of Rhizomucor miehei Rennet, which is a thermostable enzyme used in cheese production, causes undesired cases at elevated temperatures. This study aims to decrease the thermal stability of the R. miehei Rennet at high temperatures. To achieve this goal, bioconjugates of R. miehei Rennet with aldehyde derivative of dextran sulfate were synthesized in different molar ratios. Physico-chemical properties of bioconjugates were characterized with particle size analyzer and gel permeation chromatography (GPC) techniques. The enzyme and biopolymer were conjugated with medium efficiency. Milk-clotting activities of bioconjugates decreased drastically at high temperatures in all molar ratios, which reveals that covalent bioconjugation of the enzyme with aldehyde derivative of dextran sulfate caused a decrease in thermal resistance of this enzyme.

Decolorization of naphthol blue black using the horseradish peroxidase.

This study evaluates the potential of the enzyme horseradish peroxidase in the decolorization of one common industrial azo dye, naphthol blue black. Studies are carried out to understand the process parameters such as pH, temperature and reaction time. The enzymatic decolorization of the dye was examined by UV-Vis spectrophotometer and LC-MS measurements. Temperature and pH conditions were optimized for obtaining high azo-dye decolorization. Azo-dye removal at a pH range 4-6 was found to be the highest for all temperatures. After 5 minutes of treatment, the color removal of dye was ca. 80-90%. The LC-MS and spectrophotometric analyses indicated that the decolorization of the azo dye with enzyme was due to the reduction of the azo bonds. This study verifies the viability of the use of the horseradish peroxidase in the decolorization of naphthol blue black.

Glucose oxidase-dextran conjugates with enhanced stabilities against temperature and pH.

Multipoint covalent bonding of glucose oxidase (EC 1.1.3.4) to hydrophilic natural polymer dextran and optimization of procedures to obtain, with enhanced temperature and pH stabilities, were studied. Purified enzyme was conjugated with various molecular weight dextrans (17.5, 75, and 188 kD) in a ratio of 20:1, 10:1, 1:1, 1:5, 1:10, 1:15, and 1:20. After 1 h of incubation at pH 7, the activities of purified enzyme and conjugates were determined at different temperatures (25 degrees C, 30 degrees C, 35 degrees C, 40 degrees C, 50 degrees C, 60 degrees C, 70 degrees C, and 80 degrees C), and the results were evaluated for thermal resistance. Increases in temperature from 25 degrees C to 50 degrees C did not change the activities of the conjugates. The conjugate, which was prepared with 75 kDa dextran in a molar ratio of 1:5, showed the highest thermal resistance and even the activity still remains at 80 degrees C at pH 7.0. This conjugate also displayed activity in a wide pH range (pH 4.0-7.0) at high temperatures. Conjugate, which was synthesized with 75 kDa dextran in a molar ratio of 1:5, appears to be feasible and useful for biotechnological applications.