Effect of cultivation pH and agitation rate on growth and xylanase production by Aspergillus oryzae in spent sulphite liquor

Abstract

The effects of cultivation pH and agitation rate on growth and extracellular xylanase production by Aspergillus oryzae NRRL 3485 were investigated in bioreactor cultures using spent sulphite liquor (SSL) and oats spelts xylan as respective carbon substrates. Xylanase production by this fungus was greatly affected by the culture pH, with pH 7.5 resulting in a high extracellular xylanase activity in the SSL-based medium as well as in a complex medium with xylan as carbon substrate. This effect, therefore, was not solely due to growth inhibition at the lower pH values by the acetic acid in the SSL. The xylanase activity in the SSL medium peaked at 199 U ml(-1) at pH 7.5 with a corresponding maximum specific growth rate of 0.39 h(-1). By contrast, the maximum extracellular beta-xylosidase activity pf 0.36 U ml(-1) was recorded at pH 4.0. Three low molecular weight xylanase isozymes were secreted at all pH values within the range of pH 4-8, whereas cellulase activity on both carbon substrates was negligible. Impeller tip velocities within the range of 1.56-3.12 m s(-1) had no marked effect, either on the xylanase activity, or on the maximum volumetric rate of xylanase production. These results also demonstrated that SSL constituted a suitable carbon feedstock as well as inducer for xylanase production in aerobic submerged culture by this strain of A. oryzae.

High-Level Expression and Efficient Purification of Bioactive Swollenin in Aspergillus oryzae

“…6, the swollenin synergistic activity reached its highest value of 58.2% at pH5.6. The cultivation pH has been shown to be of particular importance in respect of some enzymes production by A. oryzae [19]; the result here indicates that pH5.6 is the optimal pH value for swollenin production.…”

Production of xylanolytic enzymes by Aspergillus terricola in stirred tank and airlift tower loop bioreactors

“…The high viscosity and Newtonian behavior of culture broths of Wlamentous fungi often require the use of high agitation rates to provide adequate mixing and oxygen transfer. However, mycelial damage due to high shear stress limits the practicable range of stirrer speed values and consequently the volumetric biomass and enzyme productivity of the culture [5].…”

Influence of agitation speeds and aeration rates on the Xylanase activity of Aspergillus niger SS7

“…The optimum xylanase activity of 162 (IU/mL) was obtained in 1.0 vvm aeration rate at 0.52 m/s peripheral speed. At high peripheral speed (0.79 m/s), the decrease in xylanase production has been attributed to the effect of hydrodynamic stress, which may cause hyphal disruption and leakage of intracellular compounds (Chipeta et al, 2008). The harmful effect of the shear forces as a result of agitation intensity has been reported to cause decreased enzyme production in some filamentous fungi (Palma et al, 1996;Lenartovicz et al, 2003;Techapun et al, 2003).…”