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:
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).