Effect of pH on the Rate of Fermentation in Yeast

The experiment conducted regarding the effect of pH upon the rate of fermentation in yeasts was composed of two main parts or set of procedures. The first part of the experiment was focused upon the analysis of changes or shifts in pH induced by yeast samples that are placed in varying levels of pH. From the results gathered, it was rather apparent that there was not much change upon initial and final readings. However, it still provides insights regarding the relative rate of reaction present for each pH level.

It is evident based upon the results that no change in pH levels have been detected for tubes that started with pH levels above 5. On the other hand, there were changes in initial and final pH readings for the tubes with initial pH readings below 5. To be specific, tube 2 which had an initial pH reading of 4. 7 had a final pH reading of 4. 5; this implies that there has been an increase in acidity.

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The same trend was observed in Tube 1, but there was a greater increase in acidity as there was a 0.

5 drop in pH level between initial and final readings. From the second part of the experiment, the differences in terms of the amount of gas evolved from fermentation tubes with different levels of pH were assessed in order to support or negate the findings from the first part. In this case, the amount of gas evolved from different fermentation tubes were measured in relation to varied pH levels. The results presented a general trend of increased gas evolution in acidic pH levels.

The tube with pH 4 presented a final measurement of 17mm while the tube that had a pH of 6 exhibited a final reading of 20mm. The two tubes were surpassed by the readings derived from the tube that had a pH of 5; in fact, the final reading from it was 30mm which is significantly greater than the results gathered from pH 4 and pH 6 tubes. In contrast to the tubes having evident gas evolution measurements, the tubes with non acidic pH or those with pH 7 and above had no significant readings. Discussion

The relationship between pH and fermentation rate have become evident due to the results gathered from the experiment. Since the main waste products of fermentation are carbon dioxide and ethanol, a shift in pH levels may be observed. Given that fermentation products in the form of ethanol, are able to decrease pH levels of the surroundings of the yeast as the fermentation process occurs, then the greater the decrease in pH observed the faster the rate of metabolic processes (El-Mansi and Bryce, 1999).

In addition, carbon dioxide may also confer acidity if interaction with water is allowed, thus formic carbonic acid. From the experimental results derived from the first part of the experiment, it can be determined that the fastest rate of fermentation occurs around pH levels of 4 to 5 due to the fact that the most increase in terms of acidity was observed from those pH levels. As for the tubes with higher pH levels, no significant changes in pH were observed hence implying that fermentation does not occur at neutral to high pH levels.

As for the second part of the experiment, the greater the measurements of gas evolved means that greater rates of fermentation are present. As already mentioned, this line of thought may be explained by the fact that the faster the rates of fermentation, the greater release of waste products are observed (El-Mansi and Bryce, 1999). In this case, the product assessed was carbon dioxide. The results of the second part of the experiment mainly agree with the results and implications derived from the first.

The difference was in terms of the results in fermentation rate for pH 6, as in the first part of the experiment there was no indication of fermentation while in the second part there was a significant increase in waste product release. Setting this aside, and looking at the general concept that can be derived from the results, it becomes apparent that the rate of fermentation was indeed affected by pH levels. In fact, fermentation occurs and its rate is increased at lower or acidic pH levels, with pH levels of around 4 to 5 being capable of inducing the greatest increase in fermentation rate.

However, it was not determined up to what acidic pH level can the fermentation process occur. In relation to the results, such a trend in terms of activity may also be observed if enzyme activity is to be assessed in the presence of varied levels of pH. The reason behind this is that the main driving forces for fermentative processes are in fact enzymes (El-Mansi and Bryce, 1999). Thus, enzymes in general will also be affected by different levels of pH also having specific levels wherein the greatest rate or activity may be observed.

Also, aside from enzymes, another important aspect of the fermentative process is the lack of oxygen. This is the reason as to why oxygen is exhausted or eliminated in fermentation setups. The concept behind this is that fermentation is simply an alternative mechanism for yeast to conduct metabolic process; the main mechanism utilized by yeasts is of course still aerobic cellular respiration (El-Mansi and Bryce, 1999). Therefore, if anaerobically grown yeast is transferred into an aerobic environment, then it will shift into its primary metabolic pathway.

The reason for this preference is that aerobic respiration is more efficient and provides more energy yield than fermentation (El-Mansi and Bryce, 1999). In addition, if such a transfer into aerobic conditions occurs, then the concentration of oxygen in the specific environment will surely decrease as oxygen is utilized in the process of cellular respiration. An additional analysis regarding metabolic rate may be done regarding temperature. In order to test the effects of varied temperature levels towards the rate of fermentation, a similar approach to the one utilized in the second part of the experiment may be used.

Instead of the tubes being treated with different pH conditions, each tube will be immersed in water baths of different temperatures for a specified amount of time, or if present, an incubator may prove to be a better alternative. It is a proven fact that temperature has an effect on the fermentative process since in industrial applications it is one of the main controlled factors for keeping production at an efficient pace (El-Mansi and Bryce, 1999).

Again, just like pH, the basic metabolic rate will be affected by different increments in temperature due to the fact that the enzymes that control the rate of the fermentation process have specific temperatures wherein the rate of reaction or productivity is optimal (Neway, 1989).

References

1. El-Mansi, E. M. T. and Bryce, C. F. A. (1999). Fermentation Microbiology and Biotechnology.
2. United States of America: CRC Press – Taylor and Francis. Neway, J. (1989). Fermentation Process Development of Industrial Organisms. Biotechnology