ABSTRACT
Beneficial microorganisms are used in foods in several ways. These include actively growing microbial cells, nongrowing microbial cells, and metabolic byproducts and cellular components of microorganisms. An example of the use of growing microbial cells is the conversion of milk to yogurt by bacteria. Nongrowing cells of some bacteria are used to increase the shelf life of refrigerated raw milk or raw meat. Many byproducts, such as lactic acid, acetic acid, some essential amino acids, and bacteriocins produced by different microorganisms, are used in many foods. Finally, microbial cellular components, such as single-cell proteins (SCPs), dextran, cellulose, and many enzymes, are used in food for different purposes. These microorganisms or their byproducts or cellular components have to be safe, food grade, and approved by regulatory agencies. When the microbial cells are used in such a way that they are consumed live with the food (as in yogurt), it is very important that they and their metabolites have no detrimental effect on the health of the consumers. When a byproduct (such as an amino acid) or a cellular component (such as an enzyme) is used in a food, the microorganisms producing it have to be regulated and approved, and the byproduct and cellular component have to be safe. If a food-grade microorganism is genetically modified, its use in food has to be approved, especially if the genetic material used is obtained from a different source or is synthesized. Thus, the microorganisms used for these purposes have to meet some commercial and regulatory criteria. In this chapter, characteristics of some microorganisms used in the processing of foods (designated as fermented foods) are discussed. Many of these microorganisms are used to produce several byproducts and cellular components used in foods.
