Assessment of pectinase production by Aspergillus oryzae in growth-limiting liquid medium under limited and non-limited oxygen supply

• Conditions that resulted in less interference of the rheology on the process were defined.
• A delayed addition of pectin allowed an effective control of dissolved oxygen.
• At pH 4.0, cell growth is strongly encouraged but there is no pectinase production.
• At pH 2.7, both pectinase production and stability are favored.
• An unlimited oxygen supply is essential to achieve high activities of pectinases.

The cultivation of Aspergillii in liquid media is often hindered by the intense consumption of oxygen by the fungi. In this work, pectinase production by Aspergillus oryzae IPT-301 was assessed in cultures grown with limiting and non-limiting oxygen supplies to evaluate the effects of pH and the concentration of dissolved oxygen on the process. Different strategies – such as the use of a growth-limiting medium and the delayed addition of inducer (citrus pectin) to the bioreactor – were employed to provide an effective oxygen supply to the microorganisms and to avoid excessively high impeller speeds that could damage the fungal hyphae. In a limited oxygen environment, it was observed that the maintenance of a constant pH value of 4.0 throughout the cultivation resulted in high cell mass concentration but no enzyme activity. However, when the pH was kept at 4.0 only during the period of intense cell growth followed by sustained control at pH 2.7, significant enzyme activity was detected (43 U mL−1). It was observed that this low pH favors both the production of enzyme and their stability. Under a non-limiting dissolved oxygen concentration, over 30% of saturation, the delayed pH control approach resulted in the maximum pectinase activity of 120 U mL−1.