Scale up studies and determination of growth and polygalacturonase formation kinetics of aspergillus sojae mutant strain

Abstract

The complex structure of the submerged fungal fermentations makes the kinetic parameter estimation difficult due to the problems like settling of mycelial clumps, less uniform distribution of biomass and because of the use of heterogeneous medium. Therefore in thecurrent study the aim was to kinetically evaluate the growth and production of polygalacturonase by Aspergillus sojae mutant strainin 1 l serial bioreactor systemby applying different techniquesto biomass data of whole orange peel (WOP) fermentation. With this perspective, spectrophotometric technique, sample blank subtraction method, adaptation of a new sampling port, application of cube root kinetics and different linearization methods and glucoseamine content determination methods were applied. With the new sampling port, reasonable biomass results were obtained due to the provision of homogeneous sampling. Overall, maximum PG activity was achieved at 600 rpm agitation speed, 1.5 vvm aeration rate and uncontrolled pH conditions. The highest polygalacturonase activity (249.49 U/ml) obtained was quite higher than our previous findings. The maximum specific growth rate (μ) of Aspergillus sojae mutant strain was estimated as 0.21 h-1 and 0.40 h-1 for WOP and EOP, respectively. Fed-batch fermentation technique was observed to increase the PG production yield 60% and 54% more than the batch fermentation of WOP and EOP, respectively.Moreover, crude PG enzyme showed significant activity at the acidic pH region (4.0 – 5.0) and was stable in a broad pH range (3.0 –11.0). Optimum temperature for maximum PG activity was observed at 60°C, however the enzyme could not present any thermostability above 40°C.