Introduction


We have been using enzymes for thousands of years to make various drinks and things to eat, such as cheese, yoghurt, bread, beer, and wine. Of course the people who first discovered how to make these knew nothing about enzymes. In this unit we can see how these amazing biological catalysts are used in making these traditional foodstuffs, and also in making new products.

Human beings have been making wine and beer for at least the past 8,000 years. No one knows for certain how the practice started, but it is possible that the first wine was made when squashed grapes became fermented and someone decided to taste the juice (and liked it!). Have you ever noticed the white 'bloom' on the skin of a grape? This is a natural form of a fungus called yeast. So leaving the grape juice around lets the

yeast

Yeast is a fungus whose enzymes aid the breakdown of sugar (glucose) into alcohol (ethanol) and carbon dioxide in the absence of oxygen. It is used in the brewing and baking industries.

yeast feed on the sugars in the juice and produce alcohol.

The enzymes in yeast break down sugar (glucose) into alcohol (ethanol) and carbon dioxide gas:

glucose    ethanol  +  carbon dioxide
C₆H₁₂O₆(aq)    2 C₂H₅OH(aq)  +  2 CO₂(g)

This reaction, which takes place in the absence of oxygen, is called fermentation.

Look at the experiment in Fig.1 below:

Fermentation

Fermentation is the breakdown of glucose (and other sugars) into alcohol (ethanol) and carbon dioxide by enzymes in yeast (in the absence of oxygen).

Fermentation works best if the yeast and glucose solution are kept warm. That's why home brewers leave their fermenting mixtures in the airing cupboard. (Remember that enzymes work best at their optimum temperature, but become ineffective if the temperature gets too high.)

We use the fermentation reaction to make all alcoholic drinks. However, stronger drinks, such as whisky or vodka, have to be distilled after fermentation to increase the concentration of the ethanol in the fermented mixture. This is because the ethanol poisons the yeast and stops it working when its concentration builds up to about 18 per cent by volume.



As well as its use in the brewing industry, we also use fermentation in bakeries to make bread rise. When you make bread, the ingredients are usually flour, salt, yeast, sugar, and water. When these have been mixed together they form the dough that will be baked to make the bread.

However, before it goes into the oven, we have to leave the dough for at least an hour in a warm place. This gives the enzymes in the yeast a chance to break down the sugar and make carbon dioxide gas (and ethanol, but that's not important in this particular use). The carbon dioxide gas gets trapped in the dough and makes it rise. The bubbles expand further in the hot oven when we bake the bread.

Since the 1950s,

enzyme

An enzyme is a biological catalyst which speeds up reactions in living things. An enzyme is a protein molecule with a specific shape to accommodate reactant molecules.

enzyme technology has really taken off. It is the basis of the new industry called biotechnology. There are great benefits in using enzymes as catalysts to make products. They can be some 10,000 times more efficient than ordinary inorganic catalysts used in industry. One enzyme

molecule

A molecule is a group of two or more atoms bonded together.

molecule can catalyse 10 million reactions in a single second! They also work at relatively low temperatures (typically, about 40 °C), saving energy and therefore saving money.

Do you enjoy eating those chocolates with the soft, gooey centres? If so, you might have wondered how they get the centres inside the chocolate casing. The answer is that the chocolate is poured over a solid mixture which contains sucrose (the sugar we add to tea or coffee) and an

enzyme

An enzyme is a biological catalyst which speeds up reactions in living things. An enzyme is a protein molecule with a specific shape to accommodate reactant molecules.

enzyme. The chocolate sets, and then the enzyme breaks down the sucrose into glucose and fructose. These smaller sugar molecules are much more soluble than sucrose and dissolve in the small amount of water in the original mixture.

Look at the table below showing some uses of enzymes:





We have now looked at the good points about using enzymes, but scientists have had to overcome some problems. For example, if you want to catalyse one particular reaction, you need a pure enzyme – not the mixture found in cells. But extracting pure enzymes is expensive.

Because of their cost, we need to use expensive enzymes over and over again. However, it is difficult to remove the soluble enzymes from liquid products in solution. So scientists have invented ways to trap the enzymes in place and stop them getting washed out with the products. The enzymes can be held in tiny pores inside

inert

'Inert' means unreactive.

inert structures or on beads of a substance called calcium alginate. We say that the enzymes have been immobilized. Because they are then present permanently, the reaction can be run continuously, rather than having to stop to renew the enzymes.

Summary


Sugars can be fermented with yeast to give ethanol and carbon dioxide gas.

glucose    ethanol  +  carbon dioxide
C₆H₁₂O₆(aq)    2 C₂H₅OH(aq)  +  2 CO₂(g)

The yeast, which is a type of fungus, contains enzymes which catalyse the breakdown of glucose and other sugars (in the absence of oxygen).

This fermentation reaction is used in the brewing and breadmaking industries.

There are many other uses of enzymes in the new biotechnology industries. Their use has been made more profitable by finding ways to use them over and over again by immobilizing them.