Investigation into the effect of different sugars on alcohol fermentation

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Luke Harlow        Investigation into the effect of different sugars on alcohol fermentation.          19/02/08

Investigation into the effect of different sugars on alcohol fermentation.

Abstract:

This experiment was designed to test the effect of varying sugars on ethanol production, under anaerobic conditions.

This was carried out by running a fermentation procedure for roughly a week, and distilling the resultant mixture, to determine the volume of ethanol produced.

This experiment did provide realistic changes that can be made in the future, which should result in a more effective experiment.

Aim: 

The aim of this experiment is to investigate the effect of different sugars on the production of ethanol in alcohol fermentation

Rationale:

Alcoholic fermentation occurs naturally in nature.  It can also be utilised to produce alcoholic beverages in brewing and ethyl alcohols for industrial use.

Fermentation occurs as the yeast join with the sugar molecules, and break them apart into other products. Enzymes work on a “lock and key” mechanism, by which only molecules with a perfectly matching active site can form an enzyme-substrate complex. This mechanism determines the effectiveness of the conversion of some sugars into the products. As enzymes can only form a complex with one type of molecule, there shall be some enzymes that cannot react with some of the sugars used in this experiment. For example, enzymes with the glucose matching active site cannot form a complex with lactose, and so on.

Glucose Reaction:

Glucose  Ethanol + Carbon Dioxide

C6H12O6  2 CH3CH2OH + 2 CO2

The above reaction releases 118KJ/mol.

Enzymes work by reducing the activation energy required in a reaction. This is the same function as a catalyst and enzymes are often referred to as “natural catalysts.”

This process of fermentation is most currently used in bread making, alcohol brewing and wine making. The alcohol produced during bread making is baked off and the CO2  produced is released into the atmosphere. In alcohol production, the ethanol is utilised to give the beverage alcoholic properties and the CO2 may be used to carbonate the drink.

The yeast used in this experiment was standard brewers yeast, that can withstand and still operate at much higher concentrations of alcohol than other forms of yeast. This makes this type of yeast ideal for measuring the volume of ethanol produced from sugars.

Although room temperature is not ideal for yeast activity, it is much more economical, and energy efficient. Room temperature is around 19-20°C, and optimum temperature for yeast activity occurs at around 35°C. Above this level, the yeast cells become denatured, and cease to work. Below this level, yeast activity is reduced. The higher is not being used in this experiment in order to avoid any accidents that may occur in the water baths. Yeast is active in the 19-20°C range, but is not at the optimum potential.

Sugars being used:

Glucose: 

This is the most commonly used sugar in fermentation procedures. 1 molecule of glucose, once broken down, can form 2 ethanol molecules. It is a monosaccharide sugar.

Lactose:

This is a disaccharide sugar, as it consists of 2 monosaccharide groups, glucose and Galactose. 1 molecule of lactose can form 4 molecules of ethanol.

Sucrose: Sucrose is another disaccharide sugar that consists of Glucose and Fructose. As this contains 2 of the sugars that are in this experiment, there is a chance that it could be the most effective sugar. The glucose enzymes can bind with the glucose, and the fructose enzymes can bind with the fructose molecule.

Fructose:

Fructose is a Monosaccharide with a 4 carbon ring. It can form 1 molecule of ethanol per molecule of fructose.

The key to fermentation is respiration, which can either be aerobic, or anaerobic. Aerobic respiration requires oxygen so that the reaction can take place. A lack of oxygen causes anaerobic respiration.  This reaction does not use aerobic respiration, as fermentation is occurring, which can only occur under low oxygen conditions

Cellular respiration is the name given to respiration that occurs in cellular bodies and converts fuel sources into energy. These fuel sources may be glucose and similar sugars and amino acids.

The yeast cells are the cells that carry out the cellular respiration. Due to the products from yeast respiration, the process is often referred to as ethanol fermentation. The waste products of this energy releasing reaction are Carbon Dioxide and Ethanol. The main product of ethanol fermentation is ATP (Adenosine Tri-Phosphate) which is produced in a much lower volume than aerobic respiration.

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Yeast cells use a different form of anaerobic respiration to animals. The pyruvate formed by glycolysis, is reduced to produce ethanol and carbon dioxide, instead of lactate. In this process, 2 ATP molecules are formed, releasing energy from the process.

Diagram 1 taken from http://www.chemcases.com/alcohol/

The Pyruvate is converted in Acetaldehyde, with the release of 2 carbon dioxide molecules, by the enzyme Pyruvate Decarboxylase. Acetaldehyde is then converted into ethanol by an Alcohol Dehydrogenase. The 2 H+ molecules for the ethanol are acquired from the oxidation of NADH. The 2 Hydrogen ions from the NADH are then replaced during glycolysis.

Hypothesis:

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