Yeasts oxidative

Separation of over 30 Se species feasible Se-Met accounted for 53% Se in yeast Oxidation of Se-Met occurred during sample preparation... 

Succinic Yeasts Oxidation with Acetic acid... 

A batch of Se-labeled and enriched yeast was characterized with regard to isotopic composition and content of selenium species for later use in a human absorption study based on the method of enriched stable isotopes. SeMet constituted 53% of the total Se content in the yeast. Oxidation of SeMet to selenomethionine-Se-oxide (SeOMet) occurred during sample preparation... 

CoA involved many simultaneous approaches. Many years were spent in unraveling the tangle of information obtained from studies on microbial nutrition, enzyme reactions (in addition to amine acetylation) that require CoA, yeast oxidation of acetate, and degradation and synthesis of the cofactor. The results of these studies are summarized in the following sections. 

Yeast respiratory capacity is put to good use in enology for the production of flor wines. In this case, yeasts oxidize ethanol into aldehyde in dry wines. Oxidative yeasts can also develop during winemaking they oxidize ethanol into carbon dioxide and are considered to be spoilage yeasts. 

R. sphaeroides R26, oxidized reduced yeast, oxidized reduced... 

CHjCOCOOH. A colourless liquid with an odour resembling that of ethanoic acid, m.p. 13 C, b.p. 65 C/lOmm. It is an intermediate in the breakdown of sugars to alcohol by yeast. Prepared by distilling tartaric acid with potassium hydrogen sulphate. Tends 10 polymerize to a solid (m.p. 92 C). Oxidized to oxalic acid or ethanoic acid. Reduced to ( + )-Iactic acid. 

With a special (usually oxidized or heated) odor, the result of treatment or aging ( d) Without film yeast involvement... 

Pyridine carboxamide [98-92-0] (nicotinamide) (1) and 3-pyridine carboxylic acid [59-67-6] (nicotinic acid) (2) have a rich history and their early significance stems not from their importance as a vitamin but rather as products derived from the oxidation of nicotine. In 1867, Huber prepared nicotinic acid from the potassium dichromate oxidation of nicotine. Many years later, Engler prepared nicotinamide. Workers at the turn of the twentieth century isolated nicotinic acid from several natural sources. In 1894, Su2uki isolated nicotinic acid from rice bran, and in 1912 Funk isolated the same substance from yeast (1). 

The yellow form (11) on acidification is converted to the more stable thiol form (12). On oxidation, typically with alkaline ferhcyanide, yellow form (11) is irreversibly converted to thiochrome [299-35-4] (14), a yellow crystalline compound found naturally in yeast but with no thiamine activity. In solution, thiochrome exhibits an intense blue fluorescence, a property used for the quantitative determination of thiamine. 

Diacetyl, acetoin, and diketones form during fermentation. Diacetyl has a pronounced effect on flavor, with a threshold of perception of 0.1—0.2 ppm at 0.45 ppm it produces a cheesy flavor. U.S. lager beer has a very mild flavor and generally has lower concentrations of diacetyl than ale. Diacetyl probably forms from the decarboxylation of a-ethyl acetolactate to acetoin and consequent oxidation of acetoin to diacetyl. The yeast enzyme diacetyl reductase can kreversibly reduce diacetyl to acetoin. Aldehyde concentrations are usually 10—20 ppm. Thek effects on flavor must be minor, since the perception threshold is about 25 ppm. 

Wine. The earliest known wines were made in Iran about 5400—5000 BC (25). The species of grape used is unknown and may have been either the wild grape Fitis viniferus sylvestris or a cultivated precursor of the modem wine grape V. viniferus viniferus. The source of the yeast used, and the procedures used are completely unknown. In modem times, grapes (about 21—23% sugar) are pressed the liquid must is either separated and allowed to settle for 1—2 days (for white wines) before inoculation with yeast, or the whole mass is dkectly inoculated with yeast (for red wines). In either case, while the initial fermentation takes place, the carbon dioxide formed by fermentation excludes ak and prevents oxidation. White wines are transferred to a second fermentor (racked) near the end of fermentation and kept isolated from the ak while solids, including yeast, settle out, a process that requkes about six... 

The presence of diacetyl at any stage of the process does not necessarily iadicate an infection by pediococci, because diacetyl is normally formed duting fermentation by oxidation of the precurser 2-acetolactate, which reaches a peak (1—1.2 ppm) at 24—36 h fermentation. The concentration of 2-acetolacetate is usually reduced to values of 0.01 ppm or less, and the diacetyl is reabsorbed by the yeast cells and en2ymatically transformed through acetoia to butanediol. It is extremely important that 2-acetolactate as diacetyl is reduced below the threshold of 0.05—0.10 ppm (ia terms of diacetyl). 

Physiological Role of Citric Acid. Citric acid occurs ia the terminal oxidative metabolic system of virtually all organisms. This oxidative metabohc system (Fig. 2), variously called the Krebs cycle (for its discoverer, H. A. Krebs), the tricarboxyUc acid cycle, or the citric acid cycle, is a metaboHc cycle involving the conversion of carbohydrates, fats, or proteins to carbon dioxide and water. This cycle releases energy necessary for an organism s growth, movement, luminescence, chemosynthesis, and reproduction. The cycle also provides the carbon-containing materials from which cells synthesize amino acids and fats. Many yeasts, molds, and bacteria conduct the citric acid cycle, and can be selected for thek abiUty to maximize citric acid production in the process. This is the basis for the efficient commercial fermentation processes used today to produce citric acid. 

Ethylene oxide is able to inactivate all microorganisms. Bacterial spores are more resistant than vegetative cells, yeasts, and molds (287). Spores are 5 to 10 times more resistant than the vegetative cells (288). bacillus subtilis spores were the most resistant of those tested (289). Ethylene oxide was also shown to be vimcidal (290). 

The two oxidoreductase systems most frequentiy used for preparation of chiral synthons include baker s yeast and horse hver alcohol dehydrogenase (HLAD). The use of baker s yeast has been recendy reviewed in great detail (6,163) and therefore will not be coveted here. The emphasis here is on dehydrogenase-catalyzed oxidation and reduction of alcohols, ketones, and keto acid, oxidations at unsaturated carbon, and Bayer-Vidiger oxidations. 

Self-initiated reaetions, e.g. pymvie aeid on storage ean beeome oxidized by air (or airborne yeasts) to form suffieient gaseous earbon dioxide to overpressurize the eontainer ... 

The (ZZ-ephedrine was resolved into its components by the use of d-and Z-mandelic acids. In 1921 Neuberg and Hirsch showed that benz-aldehyde was reduced by yeast, fermenting in suerose or glueose solution to benzyl aleohol and a phenylpropanolone, which proved to be Z-Ph. CHOH. CO. CH3. This ean be simultaneously, or consecutively, eondensed with methylamine and then eonverted to Z-ephedrine by reduction, e.g., with aluminium amalgam in moist ether, or by hydrogen in presenee of platinic oxide as catalyst (Knoll, Hildebrant and Klavehn ). 

InteresPng, though hardly of practical value, is the oxidation of 1 -fluorooctadecane by yeast of genus Torulopsis gropengiessen to give a 9% yield of octadecanedioic acid and a 4 5% yield of hexadecanedioic acid [/]... 

Riboflavin was first isolated from whey in 1879 by Blyth, and the structure was determined by Kuhn and coworkers in 1933. For the structure determination, this group isolated 30 mg of pure riboflavin from the whites of about 10,000 eggs. The discovery of the actions of riboflavin in biological systems arose from the work of Otto Warburg in Germany and Hugo Theorell in Sweden, both of whom identified yellow substances bound to a yeast enzyme involved in the oxidation of pyridine nucleotides. Theorell showed that riboflavin 5 -phosphate was the source of the yellow color in this old yellow enzyme. By 1938, Warburg had identified FAD, the second common form of riboflavin, as the coenzyme in D-amino acid oxidase, another yellow protein. Riboflavin deficiencies are not at all common. Humans require only about 2 mg per day, and the vitamin is prevalent in many foods. This vitamin... 

Advances in synthesis and research of oligomeric tetrathiafulvalenes 97MI9. Enantioselective oxidation of 1,3-dithiolanes to corresponding S-oxides and S,S-dioxides by designer yeast 99JHC1533. 

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