Result

Result of our one day fermentation is obtained through the measurement of absorbance and the glucose uptake.

Samples were taken at different time, starting on 24th November 2pm, then 4pm, 6pm, 8pm, 10pm and the next day (25th November) at 8am and 10am.

First, we shall look at the absorbance reading using spectrophotometer at 600nm.

Table 1: Absorbance reading at different time.

Figure 1: Graph of Absorbance vs Time

 From the first diagram, we can see that the cells start growing since 0 hr (2pm), it was at the log phase until approximately 4 hours later, it entered lag phase. Cells grew at higher rate and it reach maximum yield at time 6 hr.

After that, the cells slowly decreased. We suspect that the condition in the bioreactor inhibit the cells growth. The cells growth continuously dropped.

Other than the optical density of cells, we also estimate the cells growth by using glucose level measurement. The glucose content of the samples can be tested with the blood glucose meter.

The reading shown in the meter is in mmol/L. So, we have to convert it to mg/dL using the conversion table as shown in figure 2.

Figure 2: Conversion table for blood glucose monitoring.

Simple conversion can be calculated as the example below:

The glucose content read from biosensor at time 0 hr is 25.3 mmol/L.

Simple calculation needed for conversion:

 Table 2: Glucose level at different time. 

To calculate glucose consumed throughout the fermentation, we have to substract the glucose content used from the initial glucose content inside the bioreactor which was 2000 mg/dL.
Glucose used = 2000 mg/dL - 1821.6 mg/dL
                     = 178.4 mg/dL


Total volume of the medium was 1.5 L  (15 dL)
Therefore, 
initial glucose content in the medium 
= 2000mg/dL x 1.5 L x 10dL/1L x 1g/1000mg
= 30 g
At time=0, glucose content consumed 
= 178.4 mg/dL x 1.5 x 10dL/1L x 1g/1000mg
= 2.676 g

Table 3: Total glucose consumed at different time.

Figure 3: Total glucose consumed vs Time

From the graph, we can observe that the glucose consumption was gradually increasing until time = 4.7 hr, it had a sudden drop. However, after some times, the cells consumed glucose again at a higher rate. The cells kept utilizing the glucose supply after that.

We had not much idea with the sudden drop of glucose, it might be some error done when testing the glucose using the biosensor.

However, if we were to compare the relationship between absorbance and glucose uptake, we faced another question. Absorbance graph showed us that the cells stopped growing after sometimes. However, the continuous utilization of glucose indicate that 'some things' were using the glucose supply. Therefore, we highly doubted that there might be some other contaminants which were utilizing the glucose content.

Figure 4: The graph shown by IRIS at time=4 hr