Application of polyurethane foam matrix as immobilizer in the production of thermostable alkaline protease by Bacillus subtilis isolated from barbecue spots

Abstract

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.