Simultaneous biosynthesis of a-amylase and cellulase enzymes in a packed-bed bioreactor system

This study focused on the simultaneous production of α-amylase and cellulase enzymes through solid-state fermentation (SSF) using Bacillus amyloliquefaciens NRRL B-645 on a substrate mixture composed of maize bran and hazelnut oil cake. The optimal fermentation medium composition for each enzyme was first optimized in Erlenmeyer flasks. Subsequently, the effects of operational parameters on enzyme production were evaluated in a laboratory-scale packed-bed bioreactor. Central Composite Design (CCD) was used in both optimization steps. For α-amylase, the optimum medium consisted of 25% (w/w) maize bran, 75% hazelnut oil cake, 6.0 ml inoculum volume, and 1.6 ml nitrogen source. For cellulase, the optimal composition was 52% maize bran, 48% hazelnut oil cake, 4.8 ml inoculum volume, and 1.5 ml nitrogen source. Under these conditions, maximum α-amylase (120.3 U/g) and cellulase (1138.4 U/g) activities were obtained after 114 and 90 hours of incubation, respectively. The optimized media were then applied to the packed-bed bioreactor. The highest α-amylase activity (190.9 U/g) was observed at 0.154 L/min airflow rate, 35.8 °C temperature, and 15 g packing material. Maximum cellulase activity (1354.8 U/g) was reached at 0.164 L/min airflow, 35.5 °C, and 14.5 g packing. These results demonstrate that agro-industrial by-products can be effectively used as a mixed substrate in SSF, and that commercially valuable enzymes can be produced through proper medium and process optimization. Keywords: Solid-state fermentation, Bacillus amyloliquefaciens, Packed-bed bioreactor, α-Amylase, Cellulase, Maize bran, Hazelnut oil cake