Fermentation process refers to the conversion of sugars such as glucose to alcohol, carbon dioxide and energy in the form of ATP (Kale and Gokhale). Fermentation occurs in the absence of oxygen and converts substrates such as glucose into products such as acetate or lactic acid. During fermentation, there is no oxidation phosphorylation and thus the amount of ATP that is produced is low (Pigage, Neilsen and Greeder). One specific example of fermentation is lactic acid fermentation, which is the simplest form of fermentation. In the presence of oxygen in the cells, most organisms bypass fermentation to undergo cellular respiration (Campbell and Reece).
In the production of products such as bread, wine and beer, a fungus that is mainly used is the Saccharomyces cerevisiae as known as the baker’s yeast. In bread making, the carbon dioxide that is released causes the bread to rise. Other species and strains of yeast are also used in the bread, wine and beer production. The fermentation process of glucose by this organism may be presented using the following equation.
Production of ethanol through fermentation is mainly affected by temperatures higher or much lower than 45OC, low substrate concentration, and pH levels that are less or higher than the range of 4.0-5.0 (Lina, Zhanga and Lia). This experiment aimed to study the production of carbon dioxide at different temperatures during sugar fermentation by yeast cells under anaerobic conditions.
Materials and Methods
In a 250mL beaker, 2 teaspoons of dextrose were dissolved in 250mL of warm water (37OC). In a second beaker, the same amount of sugar was added in cold water (12OC). Two small test tubes of about 4mL in volume were calibrated using a permanent marker filling the test tube with 1mL, 2mL, 3mL and 4mL up to 15mL. When the sugar was completely dissolved, a tablespoon of dry yeast was added to each beaker, and the solution stirred until the yeast was suspended. One snap cap vial was filled with cold sugar-yeast solution and the other one with warm sugar-yeast solution almost to the top. A small test tube was filled with cold sugar-yeast solution. Using the index finger as a lid, the test tube was turned upside down and immersed into the snap cap vial containing the cold solution. The finger was released when the test tube was below the liquid level in the vial. The procedure was repeated with a second test tube using the warm solution. Time was set at zero, and the volume of gas that developed in both cold and the warm systems was measured and recorded at intervals of 10 minutes. The experiment was terminated after 2 hours.
The level of the CO2 produced at different time intervals were recorded in Table 1 below. The estimation was done to either half a unit or full unit.
Total CO2 in mL/hr was calculated as follows:
In the tube number 1, total number of carbon dioxide released was 4mL in 40 minutes. Therefore, rate of carbon dioxide produced
In the tube number 2, total number of carbon dioxide released was 2mL in 40 minutes. Therefore, rate of carbon dioxide produced
A graph of volume of gas generated against time was plotted as shown in Figure 1 below. The slope for the warm system was steeper than that of the cold system.
Figure 1: Relationship between time and the amount of carbon dioxide formed
The process of glucose fermentation and occurs when oxygen is not available and when the concentration of substrates is high (Kompala). In yeast, the process of fermentation converts sugar molecules into alcohol. This process produces carbon dioxide as a bi-product. The fermentation process is catalyzed by the enzymes that are in the yeast and this makes yeast an appropriate organism in the production of beer and wine and baking breads. It is the carbon dioxide that is produced during yeast fermentation that caused bread to rise during baking. The major alcohol that is produced is lactic acid while the fermentation producing lactic acid is referred to as lactic acid fermentation (Contreras-Govea and Muck). The rate of enzymatic reaction is highly affected by the temperature of the reaction mixture with most enzymes working within a specific range of temperatures. Yeast enzymes work best at temperatures between 35 and 45OC and temperatures exceeding 60OC may kill the yeast (Phillips).
The experiment aimed to study the production of carbon dioxide at different temperatures during sugar fermentation by yeast cells under anaerobic conditions. According to the results, the warm system with a temperature of 37OC gave the best conditions for the yeast enzymes to convert the sugar into alcohol. This was shown by the high rate of carbon dioxide production at a rate of 6mL/hour. The cold system with a temperature of 12OC did not offer the appropriate conditions for yeast enzymes to work on the sugar substrate. The low temperature lowered the rate of enzyme activity resulting into a reduced rate of carbon dioxide formation (3mL/hour).
In conclusion, the experiment successfully studied the production of carbon dioxide at different temperatures during sugar fermentation by yeast cells under anaerobic conditions. Warm conditions were indicated to be the best for the yeast enzymes to catalyze the fermentation process.
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