We all know that microbes are involved in food spoilage and food poisoning. What is less known is that besides these harmful bacteria (pathogens) there are also beneficial micro-organisms essential to our existence, and which add taste and variety to our diets.

Microbes are often thought of only as dangerous germs and little else. The fact that many of them help us in a multiplicity of ways, usually goes unnoticed. As well as aiding our digestion for example (the human gut is home to many billions of helpful microbes), they figure prominently in our daily diets.

Fermented foods are those in which desirable changes have been produced by the action of microbes. Over 3,500 traditional, fermented foods exist world-wide. They include the breads, yoghurts and cheeses familiar in Europe and North America, while in Africa foods made from fermented starch crops (such as yams or cassavas) are an important part of the local diet. In Asia, products derived from fermented soya beans or fish are consumed daily. Fermented drinks include not only alcoholic beverages, but also tea, coffee and cocoa, where the leaves or beans are fermented after harvesting, developing the characteristic flavours. Fermentation can make food more nutritious, tastier or easier to digest. It can also enhance food safety because it helps to preserve food and increase its shelf life, reducing the need for refrigeration or other energy intensive preservation methods.

Yeast is the most familiar microbe associated with food and drink. It is used in making bread, where it plays a major part in producing the spongy texture, and alcohol, which it ferments from sugars. Its use in these and other processes doubtless began by chance, but nowadays yeast cultures are prepared and added in a controlled way in food production processes. The huge industrial importance of yeast led to more than 600 scientists from 96 laboratories around the world collaborating on the Yeast Genome Project. This culminated in the publication of the complete genetic sequence of Saccharomyces cerevisiae (bakers yeast) in 1997.

The manufacture of cultured dairy products represents the second most important fermentation industry (after the production of alcoholic drinks). For instance, cheese is made in almost every country. This fermentation facilitates the conversion of the milk sugar, lactose, into lactic acid by lactic acid bacteria. This process contributes to flavour development and has a major role in preventing spoilage and the growth of pathogenic organisms. Again, the role of microbes in producing dairy products has evolved from a chance discovery to a highly elaborated process involving the production of specialised "starter" cultures. Today, a major challenge for the dairy fermentation industry is to provide stable strains of bacteria that function consistently in large-scale industrial fermentations.

There are many opportunities for using lactic acid bacteria in other ways. These include their use as beneficial bacteria in probiotic cultures, ones that supplement and help our normal gut bacteria to function more efficiently. The world-wide market for these products continues to increase in response to the demands of an increasingly health-conscious public.

Microbes are involved in the production of many other foods and they are sometimes used as food themselves. Future Food Today articles will look at some of these applications in more detail.

FOOD TODAY 09/1999