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Effects of Various Carbohydrate Substrates on Yeast Fermentation.

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Effects of Various Carbohydrate Substrates on Yeast Fermentation Abstract This experiment was performed to determine which carbohydrate substrates positively influence yeast fermentation since yeast seems to have greater ability to utilize certain carbohydrates. Rate of evolution of carbon dioxide was measured by the amount of carbon dioxide produced over time. We compared the reaction rates in samples with varying carbohydrate substrates at a constant temperature of 35 degrees C. The most efficient carbohydrates, with respect to time and energy, were the ones best suited for the yeast's "enzyme-based transport system (Vilet, 1993)", which allows entry into the yeast cell and entry into the glycolytic pathway. Those carbohydrates best suited for the enzyme-transport system had the highest carbon dioxide levels and the greatest reaction rates. Introduction For millennia, humans have used the alcoholic fermentation capability of yeast to produce breads, crackers and a variety of fermented beverages including beer and wine. Yeast are versatile unicellular fungi. They grow rapidly and have simple nutritional requirements. "When yeast degrade nutrients in the absence of oxygen they use the process of glycolysis to produce energy in the form of ATP (Klocker, 1901)".


15 ml of yeast suspension was placed in each of six tubes. Five five-percent-carbohydrate solutions were prepared. Five tubes were labeled to a specific carbohydrate; glucose, fructose, lactose, sucrose, and starch. Fifteen ml of each of the prepared carbohydrate solutions was poured into its corresponding tube. In the sixth tube, 15 ml of distilled water was added and labeled control. The opening of each tube was sealed with parafilm and each tube was mixed vigorously. Carefully, each sealed tube was tilted to ensure a gas bubble fill the tip of the arm. With all bubbles approximately the same size; a colored pencil was used to mark the levels of yeast-carbohydrate. The same was done to the control tube. All marked tubes were then incubated at 35 degrees C. Measurements along the arm of each tube were taken every thirty minutes, up to one and a half hours, of the amount in length the solution was displaced by carbon dioxide in the tube. A new colored line was made and findings during each interval were recorded (in centimeters).


Since the reaction rate is the measure of the carbon dioxide evolved over time, the greatest level of conversion was also found in the sucrose tube. The high ratio of yeast-starch to carbon dioxide (see Figure 1) caused the reaction rate to grow rapidly as well (see Figure 2). Sucrose follows the hypothesis because it enters the cell and glycolytic pathway. Sucrose is able to do this because it "consists of a glucose and fructose molecule... and its bond is easily broken by an enzyme produced by yeast (Vilet, 1993)". However, the ratio yeast-starch to carbon dioxide is greater than expected. The yeast's efficiency to use sucrose and thus the ability to break its bond is greater than any carbohydrate tested. The yeast's efficiency to use sucrose was expected to be greater than lactose (Figure 1) because yeast lacks the enzyme required to break the molecule bonded by b-galatoside in lactose, and starch (Figure 1) because of its slow rate of fermentation due to its size and inability to enter the yeast's cell efficiently. It wasn't however, expected to be greater than yeast-glucose or yeast-fructose given the fact that "glucose and a slight modified form of fructose are directly used by the glycolytic pathways (Vilet 1993)" (Figure 1).

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