Kinetics of cellulase-free endo xylanase hyper-synthesis by Aspergillus Niger using wheat bran as a potential solid substrate

Abstract

The present study deals with the production of cellulase-free endoxylanase by Aspergillus niger ISL-9 using wheat bran as a solid substrate. Endoxylanase was produced under a solid-state fermentation. Various growth parameters were optimized for the improved production of the enzyme. The Substrate level of 15 g was optimized as it provided the fungus with balanced aeration and nutrition. Among the six moisture contents investigated, Moisture Content 5 (MC5) was optimized (g/l: malt extract, 10; (NH₄)₂HPO₄, 2.5; urea, 1.0) and 10 mL of MC5 was found to give the highest production of endoxylanase. The pH and time of incubation were optimized to 6.2 and 48 h respectively. The Inoculum size of 2 mL (1.4 × 10⁶ spores/mL) gave the maximum enzyme production. After optimization of these growth parameters, a significantly high endoxylanase activity of 21.87 U/g was achieved. Very negligible Carboxymethylcellulase (CMCase) activity was observed indicating the production of cellulase-free endoxylanase. The notable finding is that the endoxylanase activity was increased by 1.4-fold under optimized conditions (p ≤ 0.05). The overall comparison of kinetic parameters for enhanced production of endoxylanase by A. niger ISL-9 under Solid State Fermentation (SSF) was also studied. Different kinetic variables which included specific growth rate, product yield coefficients, volumetric rates and specific rates were observed at 48, 72 and 96 h incubation time and were compared for MC1 and MC5. Among the kinetic parameters, the most significant result was obtained with volumetric rate constant for product formation (Q_p) that was found to be optimum (1.89 U/h) at 72 h incubation period and a high value of Q_p i.e.1.68 U/h was also observed at 48 h incubation period. Thus, the study demonstrates a cost-effective and environmentally sustainable process for xylanase production and exhibits scope towards successful industrial applications.

Keywords: Aspergillus Niger; Endoxylanase; Optimization; Solid state fermentation; Xylan.

Fig. 1

Effect of different substrate levels on endoxylanase activity by A. niger Isl-9 under SSF. Incubation temperature 30 °C, distilled water 10 mL, incubation period 72 h, inoculum size 1 mL

Fig. 2

Effect of different moisture contents on endoxylanase activity by A. niger Isl-9 under SSF. Incubation temperature 30 °C, wheat bran 15 g, incubation time 72 h, inoculum size 1 mL

Fig. 3

Effect of different initial pH of the moisture content on endoxylanase activity by A. niger Isl-9 under SSF. Incubation temperature 30 °C, wheat bran 15 g, moisture content (MC5) 10 mL, incubation time 72 h, inoculum size 1 mL

Fig. 4

Effect of different volumes of moisture content on endoxylanase activity by A. niger ISL-9 under SSF. Incubation temperature 30 °C, wheat bran 15 g, pH 6.2, incubation time 72 h, inoculum size 1 mL

Fig. 5

a Effect of different times of incubation on endoxylanase activity by A. niger Isl-9 under SSF. b Effect of different times of incubation on protein content of enzyme by A. niger Isl-9 under SSF. c Effect of different times of incubation on the turbidity of fermentation broth by A. niger Isl-9 under SSF. d Effect of different times of incubation on the final weight of the substrate by A. niger Isl-9 under SSF. e Effect of different times of incubation on final pH of fermentation broth by A. niger Isl-9 under SSF. Incubation temperature 30 °C, wheat bran 15 g, MC1 10 mL at pH 7.8, MC5 10 mL at pH 6.2, inoculum size 1 mL)

Fig. 6

a Effect of different inoculum size on endoxylanase activity by A. niger Isl-9 under SSF. b Effect of different inoculum sizes on the protein content of the enzyme by A. niger Isl-9 under SSF. c Effect of different inoculum sizes on the turbidity of fermentation broth by A. niger Isl-9 under SSF. Incubation temperature 30 °C, wheat bran 15 g, moisture content 10 mL, pH 6.2, incubation time 48 h,72 h