You will experiment with alcohol fermentation in this lab. Alcohol fermentation

Question

You will experiment with alcohol fermentation in this lab. Alcohol fermentation by yeasts is used in making beer, wine, spirits, and bread. In bread-making, yeast ferments the sugars in the dough producing carbon dioxide which create "holes" in the bread- this causes the bread to rise ("leavening) - the alcohol evaporates during the baking process. Yeast fermentation of sugars in grape juice or grains is used to produce alcoholic beverages In alcohol fermentation, the 3-carbon pyruvate molecule is broken down into a 2-carbon compound, acetaldehyde and a 1-carbon compound-carbon dioxide gas (Figure 1). Acetaldehyde is converted into ethanol using reducing power from NADH which gets converted to NAD+. This reaction regenerates the supply of NAD+ needed for glycolysis. Thus, for every molecule of glucose fermented, 2 ethanol molecules, 2 carbon dioxide molecules, and 2 ATP molecules (compared to 38 ATP in aerobic respiration) are produced Glucose + 2 ADP + 2P1 2 ethanol + 2 ATP + 2 CO2 How could you use this information to measure fermentation rates? 1 pt

Explanation / Answer

In order to measure the fermentation rate, we can consider three factors:

1. amount of glucose lost through anaerobic respiration.

2. amount of alcohol generated.

3. amount of carbon dioxide evolved.

Disappearance of glucose as substrate molecule and appearance of ethanol gives the direct measurement of fermentation reaction that is taking place. Amount of ethanol produced can be checked by treating the alcohol with PCC (pyridinium chlorochromate) that will produce chromate (orange-brown colored complex). The absorbance of the colored solution is measured by taking out small aliquots of samples after particular time intervals. Ethanol has Lambda max value at 570 nm. After that the % ethanol is tested by doing ethanol assay that employs the use of ethanol oxidase which is specific for primary alcohol and gives linear results for ethanol when it is being titrated.

secondly, with the help of the respirometer, amount of carbon dioxide released can be measured and further quantified. As the fermentation reaction progresses, amount of carbon dioxide increases. To check that its carbon dioxide released during anaerobic respiration, lime water or calcium hydroxide is brought near the reactor. The milkiness of lime water indicates the evolution of this gas.

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