Influence of volumetric oxygen transfer coefficient (kLa) on xylanases batch production by Aspergillus niger van Tieghem in stirred tank and internal-loop airlift bioreactors

Oxygenation is an important parameter involved in the design and operation of mixing-sparging bioreactors and it can be analyzed by means of the oxygen mass transfer coefficient (k(L)a). In this study, batch fermentations in stirred tank bioreactor (STB) and airlift bioreactor (ALB) were operated under a range of k(L)a values, in attempts to optimize and compare the activities of extracellular xylanase and beta-xylosidase synthesized by the fungus Aspergillus niger van Tieghem, using corncob as inducer source. The higher xylanase levels were observed on SIB (9000 U l(-1); k(L)a = 30 h(-1)), while the beta-xylosidase production was similar in both bioreactors. However, when the enzymatic activity was compared for the same k(L)a value (12 h(-1)) in SIB and ALB, the xylanase and beta-xylosidase productions were higher in ALB (7000 U l(-1) xylanase; 2100 U l(-1) beta-xylosidase) than SIB (4500 U l(-1) xylanase; 1800 Ul(-1) beta-xylosidase). (C) 2013 Elsevier B.V. All rights reserved.