Lactic yeast

In the first stage of the first two strategies, anaerobic mesophilic conditions allow the development of activity of Streptococcus sp. and "lactic yeast" (isolated from blue Stilton whey), which consume lactose and produce lactate, ethanol and carbon dioxide, and further biomass. In the second stage, aerobic conditions are employed which are favorable to the activity of an added mixed population of Bacillus sp., which degrades all available organic acids and ethanol, producing CO2 and further biomass. 

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. 

Fermentation Feedstock. Sucrose, in the form of beet or cane molasses, is a fermentation feedstock for production of a variety of organic compounds, including lactic, glutamic, and citric acids, glycerol, and some antibiotics. Lesser amounts of itaconic, aconitic, and kojic acids, as well as acetone and butanol, are also produced (41,51—53). Rum is made by fermentation of cane molasses. Beet and cane molasses are used for production of baker s and brewer s yeast (qv). 

Molasses is also used as an inexpensive source of carbohydrate in various fermentations for the production lactic acid, citric acid, monosodium glutamate, lysine, and yeast (60). Blackstrap molasses is used for the production of mm and other distilled spirits. 

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 production of soda crackers is also based on a mixed fermentation. Doughs for cracker production are inoculated with very smaH amounts of bakers yeast. During the first 3—5 h of the 18-h fermentation, yeast activity predominates thereafter bacterial fermentation causes a rapid decrease in pH through formation of lactic acid. 

Beer taste can be spoiled by contaminating bacteria or yeasts. The most common bacteria are lactic and acetic acid producers and T ymomonas. Wild yeasts can be anything other than the intended strain S. uvarum is considered a contaminant of ale fermentations and S. cerevisiae a contaminant of lager fermentations. The common wild yeast contaminants are S. diastaticus and species of Picbia, Candida and Brettanomjces. It may be noted that the flavor of beer may be improved by the ability of yeast to adsorb bitter substances extracted from hops, such as humulones and isohumulones. 

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. 

Commercial Alcoholic beverages Sauerkraut Pickles Cheeses Lactic acid Various yeasts, molds, and bacteria L. plantatum plus other bacteria L. plantaixim plus other bacteria Propionibacteria, molds, and possibly many other microorganisms Two lactobacillus species... 

Since 673 kcal/mole could be released by complete oxidation, we might wonder why the yeast cells (and muscle) extract only 20 kcal/mole and leave so much of the potentially available energy untouched. This extra energy is there in ethanol and lactic acid and could be released if these compounds were oxidized further to C02. 

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). 

The above observations suggested that hexoses arise in Nature by reaction of glycerose with dihydroxyacetone. A vast amount of practical information has been derived from investigation of plant- and muscle-extracts, two dissimilar systems that show many similarities in their biosynthetic manipulations. There is a close parallelism in the sequence of intermediates involved in the processes wherein D-glucose is converted to ethanol and carbon dioxide by yeasts, and to lactic acid by muscle during contraction. The importance of these schemes lies in their reversibility, which provides a means of biosynthesis from small molecules. 

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