Result And Discussion

DATA AND OBSERVATION

Understanding the yeast behaviour by using data of Optical Density, Glucose and IRIS.

Table 1: Optical Density And Glucose Reading

No	Time (hours)	Sample code	Optical Density (600 nm) x dilution factor	Glucose (mmol/L) x dilution factor
1	1255	T0	0.882	78.960
2	1455	T2	1.382	39.400
3	1555	T3	4.980	19.100
4	1655	T4	8.670	Lo
5	1755	T5	11.350	Lo
6	1855	T6	8.400	Lo
7	1955	T7	13.965	Lo
8	2055	T8	9.612	Lo
9	2155	T9	10.660	Lo
10	2255	T10	18.660	Lo
11	2355	T11	14.325	Lo
12	0055	T12	17.125	Lo
13	0255	T14	14.730	Lo
14	0455	T16	20.125	Lo
15	0655	T18	17.320	Lo
16	0755	T19	34.920	Lo
17	0920	T20	33.705	Lo
18	0955	T21	45.150	Lo

*Lo indicates that the reading of glucose is lower than 2.0mmol/L

The figure above shows the optical density (O.D) versus time (hour). Optical density measured

by using spectrophotometer are  used to measure the concentration of bacteria in a suspension. As visible light passes through a cell suspension the light is scattered. Greater scatter indicates that more bacteria or other material is present. The amount of light scatter can be measured in a spectrophotometer. We determined the optical density at 600nm wavelength that correlates with the different phases of bacterial growth. 

Graph above shows the concentration was increase by time. As time go on, the growth of cell is increase. Thus, it leads to increase on concentration of cells within the fermenter. So that the O.D reading continuously increase by time because it measure all the dead and live cell in fermenter.

By the way, the kit indicates that the glucose is decreasing with time because the yeast continuously utilizes it as main nutrient source. After 4 hours fermentation, the glucose reading decrease dramatically to lower than 2.0mmol/L. It might be because the yeast already undergo the log phase which is the fasters growing phase.  

Figure 2: Graph reading from IRIS; consist data of Stirrer rpm (red), temperature (yellow), pH (green), pO₂ % (blue), antifoam % (dark-green), base pump ml (light-blue), AF pump ml (dark-blue)  versus time.

S.cerevisiae undergo aerobic fermentation. So, oxygen is continuously supplied into the media. Blue line shown us the percentage of dissolve oxygen and oxygen used by the cells. At the first stage of the fermentation, we can see the blue line was dropped. This condition gave us information that the yeast cells used the oxygen that dissolved in the media with proportionally helped by agitation process. Because of that, we can see the stirrer rpm (red line) inversely proportional to dissolved oxygen (blue line). The figure above gave us also information about high formation of foam at the first stage through the percentage of anti foam used. High percentage of anti foam used at the beginning because we want to break off the high of foam formation. Then, the percentage of anti foam become low and constant until the end.

While, as the fermentation go on, the medium become more acidic. It is because the production of metabolite by yeast itself. But, after certain period; it might be the time where they are not actively growing, the pH increase especially after 14 hours of fermentation. At this point, temperature and stirrer speed started to decrease where as the dissolve oxygen increase dramatically. The yeast cell might reach to the stationary phase.

CONCLUSION

After 4 day of marathon culturing Saccharomyces cerevisiae using our new 2 L fermenter, we had learned a lot. We had not only learn all the theoretical part that had been learn in lecture hall but also other problem that can be occur during fermentation process using bioreactor. Along the 4-day, we had learned and knew all the part needed to build a complete fermenter to grow microorganism. The function of all the part is specific and need to be handle with care. We also learn hoe to autoclave the whole fermenter. We also had the basic technique to inoculate microbe during fermentation process. The type of medium needed for Saccharomyces cerevisiae growth and the sterilizations process that involve in fermentation. Another precious knowledge is we learn how to use the software Iris and read the condition inside the fermenter.

Growth culture in fermenter is better and efficient than growing inside the shake flask. Living in fermenter is like a comfortable bungalow with sufficient of air, medium, dissolve oxygen, nutrient, pH and other substances that needed for the particular microbes to grow. We also had learned that to grow microbes is actually quite similar as we take care and growth our pet. We need to give them food and comfortable condition so there can growth and produce well.

THAT'S ALL.....

FROM US :

NURUL AMANI BT WALDIN

NORRABIDAH BT MOIDEN

NUR' HAMIZAH BT ZAINOL

NUR HIDAYAH BT NURDIN

NUR FAIEZAH BT A RAHMAN

NUR IZZATI BT ANUAR

PREPARED FOR :

PUAN WAN NADIAH WAN ABDULLAH

LECTURER OF BIOREACTOR DESIGN AND OPERATION (IBG 302/4)