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Polyurethane foam (PUFoam) was used as an immobilization platform
for the production of alkaline protease by Bacillus subtilis isolated
from barbecue spots. Five B. subtilis isolates were subjected to alkaline
protease assay. Among the isolates, B. subtilis IK17 exhibited highest
alkaline protease production in a 48 h single batch (peak value, 20.3 AU mL-1)
at 40 h incubation time and was selected for immobilization studies. Effects
of PUFoam volume, density and treatment in gluteraldehyde concentrations on
enzyme yield were assessed. Increase in volume resulted in increased enzyme
yield as volume of 3.375 cm3 yielded a peak enzyme value of 27.2
AU mL-1; 1 cm3 foam volume led to peak enzyme value of
24.1 AU mL-1 while 0.125 cm3 gave a peak value of 23.8
AU mL-1 at 48 h. Higher foam density led to a reduced enzyme activity
as peak values obtained at 48 h incubation showed 2 g cm-3 = 23.8
AU mL-1; 1 g m-3 = 24.2 AU mL-1 and 0.5 g cm-3
= 28.22 AU mL-1. Effects of concentrations of gluteraldehyde exhibited
maximum activity of 26 AU mL-1 for 5% gluteraldehyde followed by
25.4 AU mL-1 for 1% gluteraldehyde and 21.6 AU mL-1 for
10% gluteraldehyde. Up to 10 repeat cycles were conducted for enzyme production
using immobilized and free cells of B. subtilis IK17 with free cells
performing in only 2 cycles with peak total titre value of 100 AU mL-1
during the 1st cycle while immobilized cells produced enzyme for up to 9 cycles
with peak total titer value of 200 AU mL-1 during the 4th cycle.
The PUFoam cell leakage assessments showed that as concentration of gluteraldehyde
was reduced, it resulted in higher cell leakage. Higher cell leakage was also
observed in higher densities of foam while lower foam volumes resulted in higher
cell leakage.
