Yeast bakers

Solubility insol cold and warm H2O used as a slurry. 

Form Supplied in yellowish pressed cakes, commercially available as cubes from bakeries or supermarkets, usually produced by brewery companies. 

Handling, Storage, and Precautions the wet cake must be stored in the refrigerator (0-4 °C) and used within the date indicated by the manufacturer. 

Carbonyl Group Reductions. Early applications of BY date back to the end of the 19th century and the first examples are reductions of carbonyl compounds. The widespread applications of this biotransformation are based on some systematic investigations on various ketones and the stereochemical outcome of the reaction is generally described by the so-called Prelog s rule which successfully applies to a great number of structures (eq 1). 

The structural variety of carbonyl compounds appears to be almost unlimited since aliphatic, aromatic, and cyclic ketones are good substrates for the bioreduction. Also, organometallic carbonyl compounds such as Cr(CO)3-complexed aromatic aldehydes (eq 2) or ketones (eq 3) are enantioselectively reduced by BY. 

Industrial Biotechnology Sustainable Production and Bioresource Utilization 

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Mutation. For industrial appHcations, mutations are induced by x-rays, uv irradiation or chemicals (iiitrosoguanidine, EMS, MMS, etc). Mutant selections based on amino acid or nucleotide base analogue resistance or treatment with Nystatin or 2-deoxyglucose to select auxotrophs or temperature-sensitive mutations are easily carried out. Examples of useful mutants are strains of Candida membranefaciens, which produce L-threonine Hansenu/a anomala, which produces tryptophan or strains of Candida lipolytica that produce citric acid. An auxotrophic mutant of S. cerevisiae that requires leucine for growth has been produced for use in wine fermentations (see also Wine). This yeast produces only minimal quantities of isoamyl alcohol, a fusel oil fraction derived from leucine by the Ehrlich reaction (10,11). A mutant strain of bakers yeast with cold-sensitive metaboHsm shows increased stabiUty and has been marketed in Japan for use in doughs stored in the refrigerator (12). 

Component Bakers yeast Brewers yeast Candida sp. 

Bakers Yeast Production. Bakers yeast is grown aerobicaHy in fed-batch fermentors under conditions of carbohydrate limitation. This maximizes the yield of yeast biomass and minimizes the production of ethanol. Yeasts grown under these conditions have exceUent dough leavening capabHity and perform much better in the bakery than yeast grown under anaerobic conditions. 

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. 

Brewers and bakers dried yeasts are used as dietary supplements. They contribute some protein and trace minerals, and some B vitamins, but no vitamin C, vitamin B 2 or fat-soluble vitamins. The glucose tolerance factor (GTE) of yeast, chromium nicotinate, mediates the effect of insulin. It seems to be important for older persons who caimot synthesize GTE from inorganic dietary chromium. The ceU wall fraction of bakers yeast reduces cholesterol levels in rats fed a hypercholesteremic diet. 

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. 

So far only two groups have reported details of the use of ionic liquids with wholecell systems (Entries 3 and 4) [31, 32]. In both cases, [BMIM][PF(3] was used in a two-phase system as substrate reservoir and/or for in situ removal of the product formed, thereby increasing the catalyst productivity. Scheme 8.3-1 shows the reduction of ketones with bakers yeast in the [BMIM][PF(3]/water system. 

Preparation by fermentation of Saccharomyces cerevisiae (baker yeast) with addition of L- or DL-methionine, lyse of cells with ethyl acetate and purification by ion-exchange chromatography. 

The computational approach described above has been applied to the bakers yeast Saccharomyces cerevisiae) genome, and approximately 50 known and... 

Oxo wophorone has been reduced stereospecifically at the C=C bond by Bakers yeast, after which this product is chemically reduced at the sterically less hindered 4-oxo group to give (4R, 6R)-4-hydroxy-2,2,6-trimethylcyclohexanone, a useful building block for the synthesis of (3R, 3 /f)-zexanthis. 

Crocq et al. (1997) have synthesized trimegestone through Bakers yeast mediated reduction of a ketone (this material is a new progestomimetic molecule for the treatment of postmenopausal diseases). The key step of the multistep synthesis is the chemo-, regio- and almost stereospecific bioreduction of a triketone to the desired alcohol. 

The distinctive aroma of ammonia is often apparent in bakeries but not in the final product. Bakers yeast performs its leavening function by fermenting such sugars as glucose, fructose, maltose, and sucrose. The principal products of the fermentation process are carbon dioxide gas and ethanol, an important component of the aroma of freshly baked bread. The fermentation of the sugar, glucose—an example of a decomposition reaction — is given by the equation in Fig. 5.19.1. 

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