Bacteria in Food and Beverage Production
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Bacteria in Food and Beverage Production MICHAEL P. DOYLE AND JIANGHONG MENG
Introduction Foods are plants and animals (or their products) and each often contain many types of microorganisms. These microbes from natural and external sources contaminate foods by contact, which can occur anytime between production and consumption. Microbial contamination of foods can have many undesirable consequences ranging from spoilage to foodborne illness. However, some microorganisms possess properties that can benefit food production or conversion. Many food-grade microorganisms are used to produce a variety of fermented foods from raw animal and plant materials. The acidic, and in part organolytic, properties of fermented products result from the fermentative activities of these microorganisms. Foods such as ripened cheeses, fermented sausages, sauerkraut and pickles have not only a greatly extended shelf life compared to the raw materials from which they are derived, but also aroma and flavor characteristics contributed directly or indirectly by the fermenting organisms. Consumption of fermented food product has increased dramatically during the last two decades and will continue to increase. The production and availability of fermentative microorganisms (starter cultures) used in food conversion have advanced to meet this demand. This includes the development of novel and better strains through genetic engineering. Lactic acid bacteria (LAB) are among the most important groups of microorganisms used in food fermentations. LAB contribute to the taste and texture of fermented products and inhibit food spoilage bacteria by producing growth-inhibiting substances (bacteriocins) and large amounts of lactic acid. Many LAB benefit human and animal health, whereas others spoil beer, wine, and processed meats. They can be isolated from the respiratory, intestinal, and genital tracts of humans and animals and from plants. Fermented dairy products have been made for thousands of years, but only within the last century has the microbiological basis of these fer-
mentations been elucidated. And LAB are the principal organisms involved in fermenting dairy products. Prior to the availability of starter cultures, milk fermentations relied on the LAB naturally present in raw milk. The first commercial starter cultures, unknown mixes of strains most likely from raw milk, were prepared in Denmark just before the end of the 19th century. In the 1930s and 40s, the concept of pure single-strain starter cultures evolved, and a bacteriophage was identified as an important agent of slow fermentation in cheese. With their development in the 1960s and 70s, concentrated (often frozen or freeze-dried) starter cultures could be inoculated directly into the bulk starter vessel without the need for prior preparation in the creamery. In the last two decades, major advances on dairy starter technology have included improved culture selection procedures that enhance bacteriophage resistance. Mo
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