Effect of pH control and aeration on inulinase production from sugarbeet molasses in a bench-scale bioreactor

In this study, the effect of pH control and aeration on the production of Aspergillus niger inulinase from sugarbeet molasses in the bioreactor was investigated. The inulinase fermentations were performed at 30 degrees C temperature in 4 degrees Bx sugarbeet molasses with a 2% (v/v) inoculation rate. The fermentation medium was only supplemented with 4.2% (w/v) yeast extract. In fermentations with aeration (1 vvm), the agitation speed was gradually increased from 200 to 600 rpm. Based on the results, it was determined that the pH-(un)controlled and non-aeration inulinase fermentations caused inadequate fungal growth and thus low inulinase and invertase-type activities, specific inulinase and invertase-type activities, and low maximum production and consumption rates. On the other hand, when the fermentation broth was aerated with 1 vvm, the inulinase and invertase-type activities, specific inulinase and invertase-type activities, and maximum production and consumption rates increased significantly under pH-controlled (5.0) and pH-uncontrolled conditions. In the fermentation with aeration, the highest inulinase and invertase-type activities were yielded as 1825.38 and 1537.88 U/mL under pH-controlled and pH-uncontrolled conditions, respectively. Also, maximum specific inulinase and invertase-type activities and maximum specific inulinase production rate were found as 5361.45 and 4371.58 U/mg and 316.71 U/mL/day with pH-uncontrolled and aerated fermentation. It was found that in both non-aeration and aeration fermentation broths, the pH control had no significant effect on enzyme production (p > 0.05). The inulinase activity/invertase-type activity ratios also varied between 0.95 and 1.56, showing that the enzyme produced is inulinase since the ratios > 10(-2). Besides, with aerated fermentations, excessive and irregular fungal growth was also observed. In conclusion, aeration played a crucial role in increasing the production of inulinase and fungal growth (p < 0.05). Therefore, the best fermentation was performed under pH-uncontrolled and aeration (1 vvm) conditions (200-600 rpm agitation speed, 10 days fermentation duration, 2% (v/v) inoculum level, 30 degrees C temperature, 4 degrees Bx sugarbeet molasses, and 4.2% (w/v) yeast extract). At these conditions, inulinase and invertase-type activities were 1810.76 and 1537.88 U/mL, respectively.