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Chapter 9 : Using Microbial Succession to the Processor’s Advantage: Food Fermentation and Biocontrol
Category: Food Microbiology; Applied and Industrial Microbiology
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Food fermentation is one of humankind’s oldest methods of preservation. It is used to preserve, enhance, and add flavor to many different types of foods. In this chapter, the author examines the roles of microbes in fermentation and the general principles involved in fermentations, including how the primary fermentation organisms interact with the other microbes present in the fermentation and the roles these other microbes have in both product quality and safety. The types of substrate and fermented products can vary greatly, from fermented milk products that contain ethanol such as koumiss to the production of distilled beverages such as whiskey. A section focuses on beer and wine, two of today's most popular fermented products. The fermentation process in the case of cereals differs from the processes involved in vegetable, wine, and dairy fermentations in that it is conducted in order to create a more functional product, whereas the other fermentations are primarily conducted to increase the shelf life of the substrate. Interestingly, it was found that as with the bacterial populations, there were two separate phage-host populations, with phage from the heterolactic segment of the fermentation unable to infect bacteria from the succeeding homolactic fermentation.
EMP glycolysis pathway. The pathway is used by homofermenting LAB in food fermentations. Lactate dehydrogenase reduces pyruvate to lactic acid. Saccharomyces and other yeasts convert pyruvate to ethanol during fermentation. It is important to note that Saccharomyces is a Crabtree-positive yeast and can conduct respiration in the presence of oxygen. However, when high levels of glucose are available it uses the EMP pathway to produce ethanol, even in the presence of oxygen. Adapted from reference 55 with permission.
Phosphoketolase pathway. The pathway is used by hetero-fermenting LAB and produces ethanol, CO2, and lactic and acetic acids in equamolar amounts. Certain LAB can be facultative heterofermentative bacteria and contain both the EMP pathway and the phosphoketolase pathway, while others lacking the aldolase of the EMP pathway are obligate heterofermentative bacteria. Used from reference 55 with permission.
The propionic acid pathway. Used from reference 55 with permission.
Processor tools for controlling a fermentation