Fermentation pH in stirred tank and air-lift bioreactors affects phytase secretion by Aspergillus japonicus differently but not the particle size

Abstract

Phytases are mainly produced by filamentous fungi and have great potential for biotechnological use in animal feed treatment, because this enzyme hydrolyzes ester bonds of the phytic acid releasing inositol and inorganic phosphate. The aim of this work was to evaluate the effect of pH on the production of phytase by Aspergillus japonicus in two different bioreactors, known to have different mixing patterns—stirred tank and air-lift bioreactors. The maximum phytase production—53 U/mL—was obtained at 120 h in the stirred tank while in the air-lift the maximum value was 41 U/mL, observed at 144 h. In fermentations evaluated at controlled pH values (3.5, 6.0, and 7.5), the stirred tank was more efficient for production of phytase than the air-lift. Under these conditions, the highest value was measured at 24 h and pH 3.5. These results were not closely related to fungi particle size, because hyphae with a similar diameter (0.51–0.63 mm) and sphericity (0.78–0.87 mm) secreted different amounts of phytase under the conditions studied.

Keywords::

• pH effect
• phytase
• Aspergillus japonicus
• stirred tank
• air-lift

Acknowledgments

The authors acknowledge the technical assistance of Mr. Manuel Santos, Ricardo Alarcon, Mariana Cereia and Mauricio de Oliveira during the execution of this study.

Declaration of interest: The authors report no declarations of interest. The authors alone are responsible for the content and writing of the paper.

Financial support by National Council for Scientific and Technological Development (CNPq/Brazil), Agency for the Improvement of Higher Education Studies (CAPES/Brazil, Process 5616-09-3), National Institute of Biotechnology for Bioethanol (INCT/Brazil), State of São Paulo Research Foundation (FAPESP/Brazil, Process 2005/58878-0) and Fundação para a Ciência e Tecnologia (FCT/Portugal - Grant nr. SFRH/BD/37082/2007).