Immobilization of aspergillus oryzae β-galactosidase with carboxylated multi-walled carbon nanotubes for the production of cow milk containing prebiotic

In this study, Aspergillus oryzae β-Galactosidase (AOG) was immobilized by adsorption on carboxylated multi-walled carbon nanotubes (c-MWCNT), a commercial immobilization martix. The optimization of immobilization conditions (pH and molarity of immobilization buffer, c-MWCNT amount and immobilization time) resulted in 100.00% immobilization yield and 155.00% activity yield. In addition, characterization of free and immobilized AOG was studied. The optimum pH range (4.5-6.5) and optimum temperature (55 oC) of AOG did not change after immobilization. From Lineweaver-Burk plot, Km values for free and immobilized AOG were calculated as 31.95 g lactose / L and 20.28 g lactose / L, while Vmax values were 10.36 μmol reducing sugar / mg.dk and 16.10 μmol reducing sugar / mg.dk, respectively. On the other hand, immobilized AOG did not lose its initial activity during twenty consecutive repeated uses and twenty days of storage under optimum conditions (in 5 mL of 25 mM sodium acetate buffer pH 4.5 in a refrigerator at +4 °C). Finally, using immobilized AOG, lactose in semi-skimmed UHT cow's milk was partially converted to galactooligosaccharides (GOS) at 55 oC. Finally, using immobilized AOG, the lactose in half-fat UHT cow milk at 55 oC was partially converted to galactooligosaccharides (GOS) in milk. The initial lactose, which was 4.70% (w/v), decreased to 2.78% (w/v) at the end of the reaction for 240 minutes, while 1.79% (w/v) GOS formed from lactose and 0.13% (w/v). monosaccharide was released. Accordingly, it was found that 38.09% (w/w) of lactose was converted to GOS. Consequently, it can be said that the immobilized AOG on c-MWCNT obtained in this thesis can be used industrially in the production of GOS from lactose in milk.