Food Microbiology

Food microbiology is the study of the microorganisms which inhabit, create or contaminate food. Of major importance is the study of microorganisms causing food spoilage.^[1] However "good" bacteria such as probiotics are becoming increasingly important in food science.^[2][3] In addition, microorganisms are essential for the production of foods such as cheese, yoghurt, other fermented foods, bread, beer and wine.

Food Safety

Food safety is a major focus of food microbiology. Pathogenic bacteria, viruses and toxins produced by microorganisms are all possible contaminants of food. However, microorganisms and their products can also be used to combat these pathogenic microbes. Probiotic bacteria, including those which produce bacteriocins can kill and inhibit pathogens. Alternatively, purified bacteriocins such as nisin can be added directly to food products. Finally, bacteriophage, viruses which only infect bacteria, can be used to kill bacterial pathogens. Thorough preparation of food, including proper cooking will eliminate most bacteria and viruses. However, toxins produced by contaminants may not be heat-labile, and some will not be eliminated by cooking.

Fermentation

Fermentation is one way microorganisms can change a food. Yeast, especially S. cerevisiae, is used to leaven bread, brew beer and makewine. Certain bacteria, including lactic acid bacteria, are used to make yogurt, cheese, hot sauce, pickles and dishes such as kimchi. A common effect of these fermentations is that the food product is less hospitable to other microorganisms, including pathogens and spoilage-causing microorganisms, thus extending the food's shelf-life.

Food fermentations are ancient technologies that harness microorganisms and their enzymes to improve the human diet. Fermented foods keep better, have enhanced flavours, textures and aromas, and may also possess certain health benefits including superior digestibility. For vegetarians, fermented foods serve as palatable, protein-rich meat substitutes.^[3]

Some cheese varieties also require mold microorganisms to ripen and develop their characteristic flavors.

Asian cuisines rely on a large repertoire of fermented foods. In particular, Aspergillus oryzae and A. sojae, sometimes called koji moulds, are employed in many ways. Their hydrolytic enzymes suit them for growth on starch and other carbohydrate-rich substrates. In the koji process, fungal enzymes perform the same function as the malting enzymes used in the beer fermentations of western cultures. The koji moulds release amylases that break down rice starch which in turn can be fermented to make rice wine. Fermented rice beverages have numerous local variations and names depending on country and region. Rice wine is called shaoshing in parts of China, sake in Japan, takj or yakju in Korea, as well as by many other names across Asia. The koji moulds are also effective in a variety of legume fermentations of which miso and soy sauce are best known. Miso is a mixture of soybeans and cereals usually used to flavour soups. Soy sauce is a flavourful, salty liquid sauce made from soybeans that have been fermented by koji moulds, yeasts, as well as several halophilic bacteria. Other names for soy sauce include jiangyou (China).