Lactic acid bacteria principles

Foods that include the incorporation of microbial metabolites as part of their production are an intricate component of the world s food supply and for ethical and sensory-nutritional reasons it is essential for all the world s population to have access to this form of food. It is a process that has been in use since the early history of mankind. An Egyptian pot dating from 2300 BC (McGee, 1984) was found to contain residues of cheese and in passages in the Bible the use of some kind of fermentative starter culture is indicated. It is, therefore, possible that the use of bacteria such as the lactic acid bacteria (LAB) dates back at least four to five thousand years, although the exact principle behind the process may not have been known to the civilizations of those times (Davidson et al., 1995). Production of fermented foods, where organisms such as the LAB are involved, is a technological process that has been used for centuries at least (Herreros et al., 2005). 

Fig. 4.7. Schematic diagram of the general principle for the identification of lactic acid bacteria using specific DNAd3NA probe...

This method is based on the same principles as the many microbiological assay methods that use lactic acid bacteria (44), except that titrimetric determination of response cannot be used. One-half the maximum growth is obtained in tubes containing about 0.1 m/xg. of Bis per milliliter. The method described in this section is a modification of the methods of Davis and Mingioli (11) and Burkholder (7). 

As mentioned in the introduction, fermentation has been used since ancient times to conserve and alter food. Also today, it is still applied on a very large scale for this purpose. A few typical examples are described in this chapter. The principle is similar in most cases. Lactic acid produced by bacteria protects the food from deterioration by inhibiting the growth of mold and other microorganisms. Most vitamins and nutrients of the food are preserved during fermentation. Three examples are discussed in more detail below The production of sauerkraut, soy sauce, and milk products (Table 9.3). 

The early development of microbial processes for industrial production of ethanol or lactic acid occurred in Berfin at the Research Institute for Fermentation Industries, directed by Max Delbrfick. The major accomplishments of this institution were the preparation of pure cultures of bacteria or yeasts for industrial fermentations and the application of the principle of natural pure culturing. In natural pure culturing, the... 

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