Effect of viscosity-inducing factors on oxygen transfer in production culture of bacterial cellulose

Abstract

Bacterial cellulose (BC) production culture requires high oxygen transfer rate (representatively kLa) at a low shear force. Considering that oxygen exhaustion is observed at the latter half of the exponential growth phase where BC production actually begins, it is highly probable that the drastic reduction of kLa (oxygen volumetric transfer coefficient) is caused by the drastic increase of the soluble and insoluble viscous materials. Therefore, we examined the apparent viscosity-inducing materials generated during BC culture and investigated their effects on kLa. Using the saccharified liquid from food waste as the culture medium, we discussed the relationship between the concentration of the generated solid matters, especially BC and the viscosity, the relationship between the BC concentration and kLa, and the correlation between the viscosity and kLa. The relationship between the solid matter (BC), which is the insoluble viscosity-inducing material, and kLa showed that the BC concentration and kLa were in exponentially reciprocal proportion with the linear regression equation. In case of using agar as the soluble viscosity-inducing material, the correlation between the viscosity and kLa showed that the viscosity depending on the agar concentration was in exponentially reciprocal proportion with kLa in both tap water and the saccharified liquid medium. The results indicated that the effect of the BC concentration on kLa was not great in the saccharified liquid medium. As the agar concentration increased in tap water and the saccharified liquid medium, the viscosity was increased and kLa was decreased gradually, showing a linear relation between the logarithm of the viscosity as agar and kLa. In conclusion, the effect of the soluble viscosity on kLa was greater than that of solid matter (BC). Also, it was suggested that the soluble viscosity-inducing matters like agar were rather more effective than kLa in BC production.