The characteristics of encapsulated whole cell β-galactosidase

Abstract

We prepared encapsulated whole cell β-galactosidase using E. coli. The cell culture was divided into two steps for the cell accumulation inside the capsule and enzyme production in the cell. Growth and production media were used individually for this purpose. The dry cell weight of the free cell culture was increased 2.8 times by controlling the pH of the growth medium during cultivation. However, the weight of cells accumulated in the capsule reduced 40% with pH control. The dry cell weight increased with lactose concentration of the production medium for both cases of free and capsule cultures. The dry cell weights were 1.5 g/l for free culture and 100 g/l in the capsule when the lactose concentration of the production medium was 10 g/l. The dry cell weight increased about 60% for both cases as the lactose concentration increased from 10 to 50 g/l. The specific activity of whole cell enzyme decreased with lactose concentration from 5 to 1.4 unit/g dry cell for free culture and from 1.1 to 0.65 unit/g dry cell in the capsule. The value of Michaelis constant, K_m, of whole cell enzyme increased 3 times because of the resistance of mass transfer through the capsule membrane. The constants of Michaelis-Menten equation for the whole cell enzyme in the capsule were V_m: 0.0479 mM/min and K_m: 44.86 mM. These constants of the membrane-free cells were V_m: 0.0464 mM/min and K_m: 15.64 mM. To increase the whole cell enzyme activity, we treated encapsulated cells with organic solvents. The activity of encapsulated whole cell enzyme was increased 3.5 times with the treatment of chloroform and ethanol. The activity of the encapsulated whole cell enzymes was reserved after repeating the process 30 times.