Yeast and Sugar - the Chemistry Must Be Right

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Yeast and Sugar - The Chemistry must be right
Jansen, C.
Gymnasium Felisenum, The Netherlands

14-04-2010

Summary
Yeast can metabolize sugar in two ways, aerobically, with the aid of oxygen, or anaerobically, without oxygen. In this experiment yeast ferment sugars anaerobically. When yeast ferments the sugars anaerobically, however, CO2 production will cause a change in the weight of the sugar/yeast-solution. This raises a further question: What is the effect of different kinds of sugars on the fermentation process of yeast? The fermentation process was followed at a constant temperature and four different types of sugars were used. By measuring the release of carbon dioxide, we could see what type of sugar had the biggest effect on the fermentation process of yeast, which resulted in Sacharose.

Fermentation, sugars, yeast, carbon dioxide mass measurements

Introduction
Yeast are able to metabolize some foods, but not others. In order for an organism to make use of a potential source of food, it must be capable of transporting the food into its cells. It must also have the proper enzymes capable of breaking the food’s chemical bonds in a useful way. Sugars are vital to all living organisms. Yeast are capable of using some, but not all sugars as a food source. Yeasts reproduce rapidly through fission or budding and grow especially well in substances containing sugar.

Baker's yeast enzymes convert sugar to ethanol and carbon dioxide. Baker's yeast is cultivated from the strain Saccharomyces cerevisiae because of its superior fermentation abilities. The yeast propagates in pure culture using special culture media comprised of melasse and other ingredients. With respect to their metabolism baker' yeasts are facultative anaerobe. They can ferment or respire depending upon environmental conditions. In the presence of oxygen respiration takes place, without oxygen present, fermentation occurs. Fermentation is a process by which a living cell, such as yeast, obtains energy through the breakdown of glucose and other simple sugars. [pic]

In this experiment four types of sugars are used: Sucrose, Lactose, Fructose and Dextrose(Glucose). A disaccharide is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. For example: milk sugar (lactose) is made from glucose and galactose whereas cane sugar (sucrose) is made from glucose and fructose. The two monosaccharides are bonded via a dehydration reaction (also called a condensation reaction or dehydration synthesis) that leads to the loss of a molecule of water and formation of a glycosidic bond. The glycosidic bond can be formed between any hydroxyl group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations and stereochemistry result in disaccharides that are diastereoisomers with different chemical and physical properties.

Dissacharide (sucrose)
[pic]
Monosacharide (fructose)
[pic]
All this together raises the question: What is the effect of different kinds of sugars on the fermentation process of yeast? My hypothesis is that fructose and dextrose will produce the most CO2, because sucrose is a combination of two glucose molecules(disaccharide). Sucrose has to be further metabolized/digested to break it down into glucose molecules. The yeast already fed glucose/fructose does not have to do this, because these are monosaccharide’s. Therefore it ferments faster.

Experimental procedure and approach
First I weighted 8 portions of 1 gram of baker’s yeast. Then 45 grams of sugar: 45 grams of sucrose, 45 grams of lactose etc. Eight bottles were labeled, each with one type of sugar. There were two bottles for every type of sugar, this according to the accuracy of the experiment. Every empty bottle was filled with 250 ml of water, then marked at which point the...
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