Enzyme assay
The bacterial cells were grown at 37
o
C and
120 rpm for 120 h in Horikoshi-II medium broth.
Then the bacterial cells were removed by centrifu-gation at 6,000 rpm, 4
o
C for 10 min. The supernatant
which contains CGTase enzyme was tested for
CD-TCE complex precipitation (Nomoto et al.,
1984). The enzyme solution was sequentially
2-fold diluted in 0.2 M phosphate buffer, pH 6.0
to adjust the enzyme concentration from 1:2 to 1:2
n
dilutions. The effects of different starch types and
their concentration, including incubation temperature
were tested. The incubation time was 24 h at the indicated temperature. Then 1 mL of 100% TCE
was added and vigorously mixed by vortex. The
mixture solution was incubated in the dark for 12 h.
The CD-TCE complex was precipitated on the
inter-phase between TCE and enzyme solution. The
CGTase/CD-TCE activity was expressed as the
lowest dilution unit of the crude enzyme showing
the white pellet of CD-TCE complex.