Immobilization of β-glucosidase on different carriers and investigation of aroma-increasing effect on different tea simples

Systematic name β-D-glucoside glucohydrolase (EC 3.2.1.21) are the β- glucosidase enzyme can hydrolyze β-glucoside bonds in oligosaccharides of glucose or other compounds. β-glucosidases are mostly found in microorganisms, animals and plants. Under appropriate in vitro conditions, β-glucosidase is used for food detoxification, biomass conversion and to enhance the flavor of wine and beverages. In addition, it is used for synthesing of various commercial importance glycosides which can be used in food, cosmetics, pharmaceutical and detergent industry. Many β-glucosidases have a variety of important biological activity such as antioxidant, lowering blood glucose levels, membrane protection from freeze-thaw damage, and inhibiting the activity of tyrosinase. Although there are many studies about purification of β- glucosidase from different sources, only a few immobilization studies with this enzyme was reported. Enzyme immobilization, while continuing the catalytic activity of the enzyme, is a process wherein substantially restricted movement. Chitosan is cheap, non-toxic and non-hazardous support for enzyme immobilization. Chitosan has excellent hydrophilicity and has many advantages such as high porosity and large surface area. Enzyme immobilization can be occured via hydroxyl and amino groups. Chitosan beads' density is very close to the water and its texture is very soft. In this study, in order to increase the chitosan beads' mechanical strength, chitosan is mixed with carbon nanotube (Multiwalled carbon nanotube, MWCNTs) and Fe3O4. Characterization of composite carriers were done by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and the thermal gravimetric analysis (TGA). In this thesis study, β- glucosidase was immobilized on chitosan composite beads covalently. In the first part of the study, immobilization conditions were optimized. To optimize the immobilization conditions, optimum cross-linking time and cross-linker concentration, effect of β-glucosidase immobilization time and enzyme concentration was examined. In addition, effect of pH and temperature on the activity of free and immobilized β-glucoside was examined. Also, thermal and storge stability of free and immobilized enzyme was compared. The operational stability and reusability of immobilized β-glucoside was examined. Aroma-increasing effect of immobilized β-glucosidase on black, green, sage, balm and yerba mate tea samples was investigated. In this study, the increasing ratio of linalool, nerol, geraniol, terpineol, benzyl alcohol and 2-phenylethanol aromatic precursors were monitored by GC analysis.