Yeast 544 substitute

Agar, which is low in metabolizable or inhibitory substances, debris, and thermoduric spores, is ideal for the propagation and pure culture of yeasts, molds, and bacteria. Agar also meets the other requirements of ready solubiUty, good gel firmness and clarity, and a gelation temperature of 35—40°C and a gel melting temperature of 75—85°C. A clarified and purified form of the bacterial polysaccharide, geUan gum, is the only known satisfactory substitute. 

In this thiamine pyrophosphate-mediated process, ben2aldehyde (29), added to fermenting yeast, reacts with acetaldehyde (qv) (30), generated from glucose by the biocatalyst, to yield (R)-l-phen5l-l-hydroxy-2-propanone (31). The en2ymatically induced chiral center of (31) helps in the asymmetric reductive (chemical) condensation with methylamine to yield (lR,23)-ephedrine [299-42-3] (32). Substituted ben2aldehyde derivatives react in the same manner (80). 

Grain that is usable as food or feed is an expensive substrate for this fermentation process. A cheaper substrate might be some source of cellulose such as wood or agricultural waste. This, however, requires hydrolysis of cellulose to yield glucose. Such a process was used in Germany during World War II to produce yeast as a protein substitute. Another process for the hydrolysis of wood, developed by the U.S. Forest Products Laboratory, Madison, Wisconsin, uses mineral acid as a catalyst. This hydrolysis industry is very large in the former Soviet Union but it is not commercial elsewhere. 

For food, SCP has been produced on a smaller scale and is mainly limited to yeasts, the use of which in food has been traditional. The exception is Myco-protein, which is being promoted as a health food, rich in protein and lacking animal fat, and which can be used as meat substitutes in high-value vegetarian convenience foods. 

Sodium hypochlorite is one of the best disinfectants known, capable of killing bacteria, yeasts, fungus, spores, and even viruses. Because it is an excellent disinfectant as well as a bleaching agent, it is used in many household cleaners. Sodium hypochlorite is also used to disinfect water supplies and swimming pools (although calcium hypochlorite in powder or pellet form is often used as a substitute, due to the convenience of its solid form). 

Another example of dynamic kinetic resolution is the reduction of a sulfur-substituted ketone. Thus, yeast reduction of (R/S)-2-(4-methoxyphenyl)-l, 5-benzothiazepin-3,4(2H, 5H)-dione gave only (2S, 3S)-alcohol as a product out of four possible isomers as shown in Figure 8.39c [29kj. Only (S)-ketone was recognized by the enzyme as a substrate and reduction of the ketone proceeded... 

Consistent with the above observations, the immunoactive glucans such as curdlan (9), lentinan (10), scleroglucan (11), schizophyllan (12) and yeast glucan (13) share a common p-D(l-3)-linked glucopyronosyl backbone. Some of these polymers also contain p-D(l-6)-linked glucopyranosyl branches through the 3,6-di-O-substituted C-6 atom of the backbone residues. 

Baker s yeast reduction of y-nitroketones offers the corresponding chiral nitro alcohols, which are useful building blocks for the synthesis of chiral natural compounds.120 For example, optically active 2-substituted pyrrolidine can be prepared using the chiral nitro alcohol (Eq. 10.75).121... 

Enoate reductase reduces a,/3-unsaturated carboxylate ions in an NADPH-dependent reaction to saturated carboxylated anions. Useful chiral synthons can be conveniently prepared by the asymmetric reduction of a triply substituted C—C bond by the action of enoate reductase, when the double bond is activated with strongly polarizing groups [22]. Enoate reductases are not commercially available as isolated enzymes therefore, microorganisms such as baker s yeast or Clostridium sp. containing enoate reductase are used to carry out the reduction reaction. 

Janke, C., Magiera, M. M., Rathfelder, N., Taxis, C., Reber, S., Maekawa, H., Moreno-Borchart, A., Doenges, G., Schwob, E., Schiebel, E., and Knop, M. (2004). A versatile toolbox for PCR-based tagging of yeast genes New fluorescent proteins, more markers, and promoter substitution cassettes. Yeast 21, 947-962. 

In this context, Lindhorst et al. proposed biological investigations of pentaerythri-tol-based mannoside clusters to test their capacity to block the binding of E. coli to yeast mannan in vitro.75 In all of the proposed structures, and according to a rational approach, pentaerythritol itself, as well as the included C3 spacers, were used as structural components for substituting the inner regions of the monosaccharide moieties (Scheme 4). The tetravalent cluster 27 has been efficiently synthesized according... 

TABLE 8-1. Yeast-Mediated Kinetic Resolution of 2-Substituted Ketones via Baeyer-Villiger Oxidation... 

The same holds for substitution at C3 and C5 of the fructofuranose moiety of sucrose neither melezitose (XV)61 nor o-D-glucopyranosyl-/3-D-xyloketofuranoside (XVIc)22 is hydrolyzed by yeast saccharase. As might have been expected from the experience with glycosidases, any change in the configuration of the fructon of sucrose results in stereoisomers unhydrolyzable by /3-fructofuranosidase. Thus, methyl and benzyl a-D-fructofuranosides,62 isosucrose (= /3-D-glucopyranosyl-a-D-fructo-... 

The majority of ascomycetous yeasts form cell-wall mannans or ga-lactomannans having main chains of (1— 6)-linked a-D-mannopyrano-syl residues, often substituted at 0-2 by a-linked glycosyl groups. The linkage types in the rest of the side chains vary widely, and can consist of 2-O-substituted a- or /3-D-mannopyranosyl residues, or 3-O-substi-... 

M 25 100% yeasts c monorhamnosylmannan with minor proportions of 4-0-and 2,4-di-O-substituted a-D-Manp residues... 

Results have varied with respect to the amount of field pea flour that can be incorporated into a yeast bread before an unacceptable product is produced. Tripathi and Dat (40) made breads containing 3, 10 and 13% field pea flour and found breads made with more than 5% pea flour were not acceptable. Loaf volume decreased as the percent substitution increased. At the 5% level, color, flavor and taste of the breads were rated as excellent, but at the 10 and 15% levels, there was a bitter taste. 

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