Lactic acid produced by bacteria

Particularly preferred bacteria are those of the genera Lactobacillus or Pediococcus. Lactic acid produced by bacteria may also be used for removal of carbonate or iron scale in oil field equipment [395],... 

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). 

Prodnction of yogurt and cheese involves destabilization of the milk emulsion with the assistance of microbial activity. In yogurt, the milk is coagulated and sonred by lactic acid produced by bacteria. Cheese making starts with an enzymatic modification of the casein micelles allowing them to co-precipitate with fat droplets, thus forming the cheese curd. 

Stereoisomers of lactic acid produced by lactic acid bacteria are useful for species identification. The optical configuration of lactic acid (Table 13.1) depends on the stereospecificity of the LDH. Some microorga-... 

You can tiy working the other way, from the configurational label to the structure. Take lactic acid as an example. Lactic acid is produced by bacterial action on milk it s also produced in your muscles when they have to work with an insufficient supply of oxygen, such as during bursts of vigorous exercise. Lactic acid produced by fermentation is often racemic, though certain species of bacteria produce solely (R)-lactic acid. On the other hand, lactic acid produced by anaerobic respiration in muscles has the S configuration. 

Sourdough has long been known to improve the shelf life of bread and bakery products, primarily because of the existence of lactic acid produced by lactic acid bacteria (Lavermicocca, Valerio, and Visconti, 2003). 

Bacteria become embedded in the dextran to produce plaque, and lactic acid produced by the termentation of fructose dissolves tooth enamel. 

Lactic acid-producing bacteria associated with fermented dairy products have been found to produce antibiotic-like compounds caUed bacteriocins. Concentrations of these natural antibiotics can be added to refrigerated foods in the form of an extract of the fermentation process to help prevent microbial spoilage. Other natural antibiotics are produced by Penicillium wqueforti the mold associated with Roquefort and blue cheese, and by Propionibacterium sp., which produce propionic acid and are associated with Swiss-type cheeses (3). 

Fermentations in larger vessels and the final trade fermentation are conducted under quasi-stetile conditions, and yeast growth is accompanied by some growth of contaminant bacteria. These are generally lactic acid-producing organisms but are sometimes coHform bacteria the occurrence of Salmonella in fermentor Hquids has not been reported. Massive contamination with Oidium lactis or wild yeasts has been reported. 

The selective utilization of prebiotics by some, but not all, of the resident species alters the assemblages, densities and metabolic activities of the GIT bacteria. Of importance is the ability of prebiotics to increase the proportion of the resident bacteria represented by the lactic acid producing bacteria (LAB), resulting in changes of GIT and systemic functions (Swanson et al.. 

Lactose is readily fermented by lactic acid bacteria, especially Lactococcus spp. and Lactobacillus spp., to lactic acid, and by some species of yeast, e.g. Kluyveromyces spp., to ethanol (Figure 2.27). Lactic acid may be used as a food acidulant, as a component in the manufacture of plastics, or converted to ammonium lactate as a source of nitrogen for animal nutrition. It can be converted to propionic acid, which has many food applications, by Propionibacterium spp. Potable ethanol is being produced commercially from lactose in whey or UF permeate. The ethanol may also be used for industrial purposes or as a fuel but is probably not cost-competitive with ethanol produced by fermentation of sucrose or chemically. The ethanol may also be oxidized to acetic acid. The mother liquor remaining from the production of lactic acid or ethanol may be subjected to anaerobic digestion with the production of methane (CH4) for use as a fuel several such plants are in commercial use. 

For laboratory-scale production of casein, HC1 is usually used for acidification acetic or lactic acids are used less frequently. Industrially, HC1 is also usually used H2S04 is used occasionally but the resulting whey is not suitable for animal feeding (MgS04 is a laxative). Lactic acid produced in situ by a culture of lactic acid bacteria is also widely used, especially in New Zealand, the principal producer of casein. 

With that problem solved, we can now take up the case of the exploding Swiss cheese. Characteristic of this type of cheese are the large holes produced by the carbon dioxide gas that forms during the aging process. Cheese makers add a variety of bacteria to their creations as a way of ripening them. To Swiss cheese they also add a strain of Propionibacter shermanii. This bacterium uses the lactic acid secreted by other microbes as... 

Food can be preserved by fermentation using selected strains nf yeast, lactic acid-producing bacteria, or molds. The production of ethanol, lactic and other organic acids, and anlimicrobial agents in the food, along with the removal of fermentable sugars, can yield a product having an extended shelf life. 

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