Food production
Introduction
Previous chapters looked at the role microorganisms play in medical biotechnology. This chapter will look at the different types of microorganisms used in the food industry. It will look at some essential chemical reactions triggered by microorganisms for the production of different types of food products.
Fermentation
Fermentation is the process of anaerobic conversion of polysaccharides to carbon dioxide and ethanol by unicellular fungi - yeast. It consists of a series of chemical reactions. The simplified fermentation reaction equation for the 6-carbon sugar, glucose, is:
C6H12O6  |
2 CH3CH2OH + | 2 CO2 |
| glucose | ethanol | carbon dioxide |
The industrial process of fermentation involves growing large numbers of microorganisms for various chemical or pharmaceutical productions. Microorganisms are usually incubated under specific conditions in large tanks called fermenters. Chemical conversion by microorganisms is also referred to as bioprocessing.
The process of fermentation is used to produce wine, beer, bread and yogurt and in food preservation to create lactic acid in sour foods such as pickled cucumbers and olives. The study of fermentation is called zymology. See image 1.
Lactic acid bacteria
Lactic acid bacteria ferment lactose (a form of sugar) to lactic acid. These bacteria are usually found in milk and are also used as starter cultures in the production of cultured dairy products such as yogurt. Lactic acid bacteria are divided into two groups according to their shape: lactococci and lactobacilli (see Topic 1, Chapter 2 of this unit). See image 2.
Microorganisms used in the production of cultured dairy products such as yogurt and cheese are called starter cultures. As these microorganisms grow in milk, they convert lactose into lactic acid. During ripening of the product, the enzymes produced by the starter culture microorganims are responsible for the final product's aroma, taste and texture. Starter culture also inhibits growth of undesirable organisms. Sometimes these starter cultures are made from just one type of microorganism, in which case they are called simple, or defined, cultures. When they are made of many different types of microorganimsms they are called mixed, or compound, cultures. Starter cultures prefer different temperatures. They are divided according to their temperature preferences into mesophiles (prefer temperature around +30C) and thermophiles (prefer temperature around +55C).
Lactic acid bacteria are also used in pickling food products. During cucumber pickling, lactic acid bacteria grow and digest sugars in the cucumber, producing lactic acid. This acid gives the pickles their characteristic sour taste and it controls the spread of spoilage-causing microbes. By digesting the sugars, lactic acid bacteria remove a potential food source for bad bacteria. That is why pickling has been used as a food preservation method for centuries.
Yeast for bread making
Bread has been baked since ancient times. Bread making also depends on the activities of yeast called Saccharomyces cerevisiae. Bread dough puffs up because of carbon dioxide, which is a by-product of fermentation.
The production of carbon dioxide by yeast is needed to make the dough rise, or increase in volume. This process is called leavening. Leavening makes the dough lighter and more easily digested. Yeast cells also produce different types of organic acids and alcohol which make bread taste better. Baking evaporates any alcohol and deactivates the yeast. It also causes bubbles of carbon dioxide to move through the dough, giving the bread a spongy texture after baking. See image 3.
Yeast for wine making
Wine making is also an ancient craft. A very long time ago wild yeasts were used for conversion of grape sugar into alcohol and carbon dioxide. Wild varieties of yeast were very unreliable 'wine makers'. Cultured types of yeast, on the other hand, are consistently active and will not have any undesirable side effects.
Modern biotechnology and the food industry
When it comes to food production, biotechnology techniques have been irreplaceable for centuries.
Today, biotechnology offers techniques which help to produce better crops, plants that are naturally protected from disease and insects and potentially more nutritious, and better-tasting food products. Agricultural biotechnological methods can potentially reduce the use of pesticides.
