Acid Bacteria

Their favorable effect on growth and health is thought to be due to the modulation of other bacterial growth through one or more of these antagonistic factors. 

Although LAB are ubiquitous microorganisms widespread in a plethora of niches, they have complex nutritional requirements for amino acids, vitamins, minerals, fatty acids, peptides, nucleotide bases, and carbohydrates. These microorganisms can be found in plants, fermented foods, the gastrointestinal 

In addition to the synthesis of organic acids, many LAB can also produce other interesting metabolites such as antibacterial compounds (e.g., bacteriocins) [7], aroma compounds (diacetyl, acetoin, etc.), vitamins, exopolysaccharides (EPS), low-calorie sugars (e.g., mannitol), short-chain fatty acids, and y-amino butyric acid (GABA) [4,8]. Owing to this metabolic versatihty, these bacteria can be used as microbial cell factories in the production of chemicals, pharmaceuticals, or other industrially relevant products [1, 9]. 

This chapter deals with the biotechnological apphcation of LAB as starter cultures, although briefly, for the elaboration of fermented foods, and the production of industrially interesting metabohtes such as food ingredients, nutraceutics, and high added-value compounds. 

Riboflavin was first shown to be an junportant nutrient for bacteria by Orla-Jensen, Otte, and Snog-Kjaer (275) who worked with a number of lactic acid bacteria. Numerous subsequent studies with organisms of this group have shown that the importance of riboflavin in the nutrition of these organisms varies from species to species, and moreover can be deliberately altered in some cases. 

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In addition to alcohoHc fermentation, a malolactic fermentation by certain desirable strains of lactic acid bacteria needs to be considered. Occasionally, wild strains produce off-flavors. Malolactic fermentation is desirable in many red table wines for increased stabiUty, more complex flavor, and sometimes for decreased acidity. Selected strains are often added toward the end of alcohoHc fermentation. AH the malic acid present is converted into lactic acid, with the resultant decrease of acidity and Hberation of carbon dioxide. Obviously this has more effect on the acidity the more malic acid is present, and this is the case in wine from underripe, too-tart grapes. Once malolactic fermentation has occurred, it does not recur unless another susceptible wine is blended. 

Cells of microorganisms have constituted a portion of human food siace ancient times. Yeast-leavened baked products contain the residual nutrients from the yeast cells destroyed duriag bakiag (see Bakery processes and leavening agents). Cultured dairy products, such as yogurt, buttermilk, and sour cream, contain up to lO cells of lactic acid bacteria per gram (19) (see Milk and milkproducts). Other examples of fermented foods consumed siace early times iaclude fermented meats, fish, and soybean products. 

Lactic Acid B cteri. The lactic acid bacteria are ubiquitous in nature from plant surfaces to gastrointestinal tracts of many animals. These gram-positive facultative anaerobes convert carbohydrates (qv) to lactic acid and are used extensively in the food industry, for example, for the production of yogurt, cheese, sour dough bread, etc. The sour aromatic flavor imparted upon fermentation appears to be a desirable food trait. In addition, certain species produce a variety of antibiotics. 

After World War II, analytical methods for amino acids were improved and new methods were iatroduced. The first was microbial assay usiag lactic acid bacteria which require all of the regular amino acids for growth. Manometric determiaation (by use of a Warburg manometer) of CO2 Hberated by the... 

L-Glutamic acid "glutamic acid bacteria" such as Corymb, glutamicum Brerib. Jlavum Brevib. lactojermentum Microb. ammoniaphilum wild penicillin is added, or biotm is limited >100, 50% 21... 

Lactic acid bacteria are common contaminants of distillers fermentations. E. lactis may produce excessive amounts of volatile acids. Some species convert glycerol to fdpropionaldehyde which may break down to acrolein during distillation, producing an acrid odor. 

Yeast (qv) metabolize maltose and glucose sugars via the Embden-Meyerhof pathway to pymvate, and via acetaldehyde to ethanol. AH distiUers yeast strains can be expected to produce 6% (v/v) ethanol from a mash containing 11% (w/v) starch. Ethanol concentration up to 18% can be tolerated by some yeasts. Secondary products (congeners) arise during fermentation and are retained in the distiUation of whiskey. These include aldehydes, esters, and higher alcohols (fusel oHs). NaturaHy occurring lactic acid bacteria may simultaneously ferment within the mash and contribute to the whiskey flavor profile. 

Both prokaryotes and eukaryotes are capable of introducing a single cis double bond in a newly synthesized fatty acid. Bacteria such as E. coli carry out this process in an Og-independent pathway, whereas eukaryotes have adopted an Og-dependent pathway. There is a fundamental chemical difference between the two. The Og-dependent reaction can occur anywhere in the fatty acid chain. 

Buttersaure, /. butyric acid, -ather, tn. ethyl butyrate pi. butyric esters, -ganing, /, butyric fermentation. pilz, tn. butyric acid bacteria. 

To protect buried metals from premature breakdown it must suffice to say that protective coatings and other methods must be applied against factors such as the effects of galvanic currents, composition of the moisture in the ground, humus acids, bacteria, etc. (See Section 14.8.)... 

Some of the most notable contributions were (a) the discovery of numerous strains of lactic acid bacteria including those listed in Table XI, (b) the elaboration of the mineral... 

Table XI. History of Discovery of Common Lactic Acid Bacteria (16)...

In more recent times chemically defined basal media have been elaborated, on which the growth of various lactic acid bacteria is luxuriant and acid production is near-optimal. The proportions of the nutrients in the basal media have been determined which induce maximum sensitivity of the organisms for the test substance and minimize the stimulatory or inhibitory action of other nutrilites introduced with the test sample. Assay conditions have been provided which permit the attainment of satisfactory precision and accuracy in the determination of amino acids. Experimental techniques have been provided which facilitate the microbiological determination of amino acids. On the whole, microbiological procedures now available for the determination of all the amino acids except hydroxy-proline are convenient, reasonably accurate, and applicable to the assay of purified proteins, food, blood, urine, plant products, and other types of biological materials. On the other hand, it is improbable that any microbiological procedure approaches perfection and it is to be expected that old methods will be improved and new ones proposed by the many investigators interested in this problem. 

Orla-Jensen, S., The Lactic Acid Bacteria," Copenhagen, 1919. 

Yeast and culture starter Lactobacillus bulgaricus Lactic acid bacteria Cheese and yoghurt production... 

The sugars in fruits such as grapes are feimented by yeasts to produce wines. In winemaking, lactic acid bacteria convert malic acid into lactic acid in malolactic fermentation in fruits with high acidity. Acetobacter and Gluconobacter oxidise ethanol in wine to acetic acid (vinegar). 

Lactose is mainly used as a fermentation substrate for lactic acid bacteria in dairy products, such as yogurt and cheese. These bacteria break down lactose into lactic acid, which solidifies the milk, and creates an acid environment that favors the benign lactic acid bacteria over those that are more harmful. 

Lactic acid bacteria were immobilized in Ca-alginate beads prepared from different concentration of Na-alginate (1.0%, 2.0%, 4.0%, 6.0% and 8.0% w/v) and their fermentation efficiencies were investigated in liquid pineapple waste containing 31.3 gL of glucose... 

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