3.2 Reducing maintenance coefficient during the glycerol feeding phase by the periodic DO control strategy
According to substrate (glycerol) mass balance, maintenance coefficient using different glycerol feeding strategies could be determined by the following equation:
(1)
Here, ν , µ , Y X/S and mrepresented specific glycerol consumption rate, specific cell growth rate, cell yield on glycerol and maintenance coefficient. As shown in Fig.2, to maintain cellular homeostasis under the environments of high ROS levels (152.95 Fluorescence intensity g-DCW-1), the distribution of glycerol towards to cell maintenance reached the highest level of 0.0328 g g-DCW-1h-1 when implementing the “high DO-low glycerol concentration” control strategy (strategy A). In contrast, with the aid of the periodic DO control strategy (strategy C), ROS levels were controlled below 48.35 Fluorescence intensity g-DCW-1during the glycerol feeding phase. Accordingly, maintenance coefficient with this strategy was also kept at a lower level of 0.0198 g g-DCW-1 h-1. It should be noted that the data using the “low DO-high glycerol concentration” control strategy (strategy B) cannot be fitted with Eq. 1 and not shown in Fig.2 because cell concentration decreased obviously during the glycerol feeding phase (Fig. 1E).