In the second phase, the culture is shifted to conditions ensuring maximum specific protein production and the protein quality required.
Under the optimized conditions, the maximum specific hydrogen production rate (SHPR) was 35.74 mL/g-CDW.h based on cell dry weight.
TMB3720 and TMB3500 were clearly more efficient ethanol producers than BY, that displayed a lag phase of approximately 3 hours, a low maximum specific ethanol production rate and produced only half of the ethanol concentration (10.5 g l-1) after 50 h (Figure 4) (Table 2).
However, the maximum specific ethanol production rate was significantly higher for TMB3720, 0.08 g ethanol l-1 g wet cells-1 h-1, compared to 0.05 g ethanol l-1 g wet cells-1 h-1 achieved by TMB3500, which could be explained by the fact that the highest concentration of 19.5 g l-1 ethanol was reached only after 50 hours of batch fermentation as compared to 27 hours for TMB3720 (Figure 4).
The ultrasonic frequencies were varied as 20, 25 and 30 kHz with a maximum specific ethanol production rate of 1.55 g g−1 h−1 being achieved at 25 kHz [ 91].
It should be emphasized that most of the TCA cycle gene and protein levels were maintained or even increased up to μ = 0.40 h-1 followed by sudden repression simultaneous to achieving maximum specific CO2 production rate (μ = 0.46 ± 0.02 h-1, see above; Figure 1 Figure 2 and Figure 4A).
Intracellular carbohydrate content increased from 5 to 27% (Cmolglc.CmolX−1) in 3 hours with a maximum catalytic specific production rate of 0.074 Cmolglc.CmolX*−1.h−1.
Statistical analysis of the data showed that sucrose concentration had a large positive effect on the maximum concentration of neokestose produced, the maximum specific rate of neokestose production and the maximum yield coefficient of neokestose.
Curvature plots indicated that the optima for the maximum specific rate of neokestose production and for maximum yield coefficient were within the experimental range, whereas the optimum conditions for the maximum concentration of neokestose were outside this range.
