Yeast extracts

A fermentation such as that of Pseudomonas dentrificans typicaby requires 3—6 days. A submerged culture is employed with glucose, comsteep Hquor and/or yeast extract, and a cobalt source (nitrate or chloride). Other minerals may be required for optimal growth. pH control at 6—7 is usuaby required and is achieved by ammonium or calcium salts. Under most conditions, adequate 5,6-dimethylben2imida2ole is produced in the fermentation. However, in some circumstances, supplementation maybe required. 

The elemental and vitamin compositions of some representative yeasts are Hsted in Table 1. The principal carbon and energy sources for yeasts are carbohydrates (usually sugars), alcohols, and organic acids, as weU as a few other specific hydrocarbons. Nitrogen is usually suppHed as ammonia, urea, amino acids or oligopeptides. The main essential mineral elements are phosphoms (suppHed as phosphoric acid), and potassium, with smaller amounts of magnesium and trace amounts of copper, zinc, and iron. These requirements are characteristic of all yeasts. The vitamin requirements, however, differ among species. Eor laboratory and many industrial cultures, a commercial yeast extract contains all the required nutrients (see also Mineral nutrients). 

Other chemicals of possible concern for health and safety found ia yeast proteias iaclude tyramiae (0—2.25 mg/g) and histamine (0.2—2.8 mg/g), formed by decarboxylation of the corresponding amino acids (38). These compounds are also found ia other fermeated (including pickled) foods. Their preseace ia yeast extracts used as condiments coatributes very Htde to human iatake. Likewise, the nephrotoxic compouad lysiaoalaniae has beea ideatified ia alkah-treated yeast extracts, at a level of 0.12 mg/g. However, the chemical occurs at similar low coaceatratioas ia almost all heat- and alkaU-treated foods. 

Commercially available yeast extracts are made from brewers yeast, from bakers yeast, from alcohol-grown yeast (C. utilis) and from whey grown yeast (K fragilis). Extracts are used ia fermentation media for productioa of antibiotics, ia cheese starter cultures, and ia the productioa of viaegar. They are also exteasively used ia the food iadustry as condiments to provide savory flavors for soups, gravies and bouillon cubes, and as flavor intensifiers ia cheese products. 

In 1878 the term enzyme, Greek for "in yeast," was proposed (8). It was reasoned that chemical compounds capable of catalysis, ie, ptyalin (amylase from sahva), pepsin, and others, should not be called ferments, as this term was already in use for yeast cells and other organisms. However, proof was not given for the actual existence of enzymes. EinaHy, in 1897, it was demonstrated that ceU-free yeast extract ("zymase") could convert glucose into ethanol and carbon dioxide in exactiy the same way as viable yeast cells. It took some time before these experiments and deductions were completely understood and accepted by the scientific community. 

For this purpose a fermenter made of stainless steel having a 50 liter capacity is charged with 30 liters of a nutrient solution of 0.1% yeast extract, 0.5% cornsteep and 0.2% glucose, heated for one-half hour at 120°C for sterilization purposes, and after cooling, inoculated with a bacterial suspension of Bacillus lentus MS 2B4. 

Fe" (2 ppm), casein hydrolyzate (0.2 g/dl), yeast extract (0.2 g/dl), corn steep liquor (0.2 ml/dl), polypeptone (0.1 g/dl), meat extract (0.1 g/dl) and sodium ribonucleate (10 mg/dl) were poured into respective test tubes and each tube was sterilized at 115°C for 10 minutes. Thereafter separately sterilized calcium carbonate was added in the amount of 2 g/dl and then cells of Bacillus subtUis S26910 were Inoculated into the above media and cultured with shaking at 30°C for 20 hours. 

The yield was highest with starch or dextrin, intermediate and about the same with sucrose, glucose, maltose and lactose and poorest with glycerol. Kanamycin was produced by media containing soybean meal, peanut meal, cottonseed meal, corn steep liquor, peptone, yeast extract or meat extract, with or without sodium nitrate. Commercially available soybean meal was recognized to be one of the best nitrogen sources. The addition of corn steep liquor, peptone, yeast extract or nitrate to the soybean meal promoted the production of kanamycin. 

As described in U.S. Patent 2,929,763, methandrostenolone may be made by a fermentation route. 2 g of sodium nitrate, 1 g of primary potassium orthophosphate, 0.5 g of magnesium sulfate heptahydrate, 0.5 g of potassium chloride, 50 g of glucose and 1 g of Difco yeast extract are dissolved in one liter of tap water, brought to pH 5 by addition of a sodium hydroxide solution and sterilized. The resulting nutrient solution is inoculated with 50 cc of a 4-day-old shaking culture of Didyniel/a lycopersici and shaken for 48 hours at 27 C, whereby the culture becomes well developed. 

Nitrogen sources include proteins, such as casein, zein, lactalbumin protein hydrolyzates such proteoses, peptones, peptides, and commercially available materials, such as N-Z Amine which is understood to be a casein hydrolyzate also corn steep liquor, soybean meal, gluten, cottonseed meal, fish meal, meat extracts, stick liquor, liver cake, yeast extracts and distillers solubles amino acids, urea, ammonium and nitrate salts. Such inorganic elements as sodium, potassium, calcium and magnesium and chlorides, sulfates, phosphates and combinations of these anions and cations in the form of mineral salts may be advantageously used in the fermentation. 

The following procedure is described in U.S. Patent 2,837,464 from a solution of 3 grams of yeast extract (Difco) in 3.0 (iters of tap water containing 13.2 grams of potassium dihydrogen phosphate and 26.4 grams disodium hydrogen phosphate (pH of the solution, 6.9)... 

Beef extract T ryptone Yeast extract Dextrose Starch... 

A small fermentation tank (5,000 parts by volume capacity) was charged with 3,000 parts by volume of a culture medium (pH 6.0) comprising 3% glucose, 1 % polypepton, 0.5% yeast extract and 0.5% malt extract. The medium was sterilized by heating in a conventional manner and cooled. This medium was inoculated with 150 parts by volume of a pre[Pg.1565]

Glucose, 0.1% NaNOa, 0.01% KH2PO4, 0.05% KCI, 0.02% MgS04 x 7H2O, 3% CaC03, 0.01% yeast extract (Rathberger, Molitoris, Holler unpublished results). 

Not appropriate. Medium C would allow the growth and isolation of heterotrophs (due to the inclusion of yeast extract) and is thus not elective for methylotrophs. Also for an industrial process an organism that does not require growth factors (such as vitamins) is preferable. Medium C might well enrich for methylotrophs requring such expensive growth factors. 

Complex nutrients, such as yeast extract, are variable in composition and consequently it is difficult to maintain process reproducibility within the narrow window required to produce a product of consistent quality. 

Yeast extract source of growth factors (amino adds, vitamins, nudeotides). 

Microbial over-growth was controlled with carbon dioxide passed through the bed. There was a maximum 30% increase in the beads diameter at the lower part of column, where the glucose concentration was maximum. The void volume was measured by passing sterilised water. In addition to the carbon source, the feeding media consisted of 1 g l 1 yeast extract pumped from the bottom of the reactor, while the flow rate was constant for a minimum duration of 24 hours. 

A seed culture of S. cerevisiae ATCC 24860 (American Type Culture Collection, Manassas, VA, USA) was grown in a media of 5g glucose, and 0.5 g yeast extract, respectively, 1.5 g KH2P04 and 2.25 g Na2P04 phosphate buffer up to a total volume of distilled water, 500 ml. The media was sterilised at 121 °C for 15 min. The stock culture of the microorganisms was transferred to the broth media for preparation of seed culture. 

Take a loop full of the creamy culture off the agar plate. Dip the loop into a 250 ml flask containing 100ml of 5.0g-l 1 glucose and 1 g-1 1 yeast extract. Swirl the loop in the nutrient solution to dislodge the selected culture from the loop. 

Seed culture of Saccharomyces cerevisiae (ATCC 24860) is grown in a rich medium comprising of 1 g glucose, 0.1 g peptone and yeast extract, 0.33 g KH2P04 and 0.03 g Na2HP04 in 100 ml distilled water. The media will be autoclaved at 126 °C and 15 psig for 20 min. The stock culture from ATCC media is transferred to a prepared seed culture. The pH of... 

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