Enzymatic yeasts

Se-enriched yeast Enzymatic digestion (trypsin) SEC-ICP-MS and reversed phase HPLC-ICP-MS... 

Se-enriched yeast Enzymatic hydrolysis (/3- Gradient elution cation... 

Cantos et al. 2003 Gambuti et al. 2004). It is also influenced by yeast enzymatic activities, in particular those of isomerase and glucosidase (Jeandet et al. 1994). Equally, activities of lactic acid bacteria, which are responsible for malolactic fermentation (Hernandez et al. 2007), can also affect stilbene content in wine (Poussier et al. 2003). Aging of wine appears to have no important influence on the concentration of stilbenes (Jeandet et al. 1995). 

Along with changes in anthocyanin and tanin proportions, winemaking practices can bring additional components in wines through selection of fermentation yeasts. Enzymatic activities of particular yeast strain influence the release of volatile phenols, pyruvic acid and acetaldehyde and, therefore, control the relative proportions of the corresponding pyranoanthocyanins. 

Research into the impact of various fermentation by-products on yeast demonstrated the inhibiting effect of Ce, Cg, and Cm short-chain fatty acids found in wine at concentrations of a few milligrams per liter. They affect cell membrane permeability and hinder exchanges between the inside of the cell and the fermenting medium. When fermentation stops, the yeast enzymatic systems still function, but the sugars can no longer penetrate the cell to be metabolized (Larue etal., 1982). Salmon et al. (1993) confirmed that loss of activity... 

Dzogbefia, V.P., Buamah, R., and Oldham, J.H. (1999) The controlled fermentation of cocoa (Theobroma cacao L.) using yeasts enzymatic process and associated physico-chemical changes in cocoa sweatings. Food Biotechnol 13, 1-12. 

Biochemistry resulted from the early elucidation of the pathway of enzymatic conversion of glucose to ethanol by yeasts and its relation to carbohydrate metaboHsm in animals. The word enzyme means "in yeast," and the earfler word ferment has an obvious connection. Partly because of the importance of wine and related products and partly because yeasts are relatively easily studied, yeasts and fermentation were important in early scientific development and stiU figure widely in studies of biochemical mechanisms, genetic control, cell characteristics, etc. Fermentation yeast was the first eukaryote to have its genome elucidated. 

The function of Jisper Uis fermentation appears to be primarily the breakdown of protein and polysaccharides by secreted proteases and amylases. Replacement oiPispergillis by chemical or enzymatic hydrolysis has no major impact on the organoleptic properties of the sauce. Likewise, inoculation with a pure culture of Ixictobacillus delbrueckii to carry out the acetic acid fermentation produces a normal product. The S. rouxii and Toru/opsis yeasts, however, are specifically required for proper flavor development. 

Genetic manipulation or cloning offers many possibiUties and perhaps there will be yeast strains especially designed for special beers, ie, types, which are usehil because of low diacetyl formation, high—low ester formation, and insensitivity to pressure or high fermentation temperatures or extracellular enzymatic abiUties (P-glucanases). 

Starch is converted enzymatically toglucose either by diastase present in sprouting grain or by fungal amylase. The resulting dextrose is fermented to ethanol with the aid of yeast, producing CO2 as a coproduct. Other by-products depend on the type of process. 

Fermentation An anaerobic bioprocess. An enzymatic transformation of organic substrates, especially carbohydrates, generally accompanied by the evolution of gas as a byproduct. Fermentation is used in various industrial processes for the manufacture of products (e.g., alcohols, organic acids, solvents, and cheese) by the addition of yeasts, moulds, and bacteria. 

ENZYMATIC ANALYSIS WITH CARBOXYPEPTIDASES. Carboxypeptidases are enzymes that cleave amino acid residues from the C-termini of polypeptides in a successive fashion. Four carboxypeptidases are in general use A, B, C, and Y. Carboxypeptidase A (from bovine pancreas) works well in hydrolyzing the C-terminal peptide bond of all residues except proline, arginine, and lysine. The analogous enzyme from hog pancreas, carboxypeptidase B, is effective only when Arg or Lys are the C-terminal residues. Thus, a mixture of carboxypeptidases A and B liberates any C-terminal amino acid except proline. Carboxypeptidase C from citrus leaves and carboxypeptidase Y from yeast act on any C-terminal residue. Because the nature of the amino acid residue at the end often determines the rate at which it is cleaved and because these enzymes remove residues successively, care must be taken in interpreting results. Carboxypeptidase Y cleavage has been adapted to an automated protocol analogous to that used in Edman sequenators. 

In contemporary societies replete with various industries and automobiles, NO (NO, N02, and N03) has been recognized to be one of the important factors responsible for air pollution. Only two decades ago, NO was found to be an essential molecule that regulates cellular/molecular functions in mammals. NO is also enzymatically synthesized in nonmammals, invertebrates, and yeasts. Therefore, the origin of NO may date back to the birth of life arising from single cell organisms living around 3-billion years ago. 

Soluble organic solvents have often been used as cosolvents to solubilize miscible organic substrates. Since organic compounds including solvents are possibly incorporated inside of the enzyme, they may affect the stereoselectivity of enzymatic reactions. For example, dimethyl sulfoxide (DMSO) (10%) enhance not only chemical yield but also enantioselectivity of yeast reduction. Thus, the poor yield of 23% with 80% ee was increased to 65% yield with >99% ee (Figure 8.20) [17]. 

In addition to the catalytic action served by the snRNAs in the formation of mRNA, several other enzymatic functions have been attributed to RNA. Ribozymes are RNA molecules with catalytic activity. These generally involve transesterification reactions, and most are concerned with RNA metabofism (spfic-ing and endoribonuclease). Recently, a ribosomal RNA component was noted to hydrolyze an aminoacyl ester and thus to play a central role in peptide bond function (peptidyl transferases see Chapter 38). These observations, made in organelles from plants, yeast, viruses, and higher eukaryotic cells, show that RNA can act as an enzyme. This has revolutionized thinking about enzyme action and the origin of life itself. 

An enzymatic process using partially purified pyruvate decarboxylase (PDC) with added pyruvate overcomes the problems of benzyl alcohol formation and limiting availability of pyruvate [3]. As a result increased concentrations, yields and productivities of PAC were achieved with concentrations of PAC in excess of 50 g f (330 mM) in 28 h and yields on benzaldehyde above 95% theoretical [4-6]. Screening of a wide range of bacteria, yeasts and other fungi as potential sources of stable, high activity PDC for production of PAC confirmed a strain of the yeast Candida utilis as the most suitable source of PDC [7]. 

An IL solvent system is applicable to not only lipase but also other enzymes, though examples are still limited for hpase-catalyzed reaction in a pure IL solvent. But several types of enzymatic reaction or microhe-mediated reaction have been reported in a mixed solvent of IL with water. Howarth reported Baker s yeast reduction of a ketone in a mixed solvent of [hmim] [PFg] with water (10 1) (Fig. 16). Enhanced enantioselectivity was obtained compared to the reaction in a buffer solution, while the chemical yield dropped. 

The yeast strain SCPP exhibits all of the panoply required for the degradation of pectins from various sources. This enzymatic machinery is secreted into the growth medium. Hence, we developped interest on the regulatory mechanisms controlling the synthesis of the main activity produced by the SCPP strain, i.e. the polygalacturonase. 

The Pectolyase Y-23 and the purified yeast PG were immobilised as described by Coletti-Previero et al. [14]. 5 g of y-alumina spheres, previously equilibrated in 200 ml of a buffered solution at pH 6.0, was treated first with 30 ml of 0.04 M o-phosphorylethanolamine and then with 30 mL of 0.56 M glutaraldehyde. These two reactions were performed at 25 C and pH 6.0, for 1.5 h and were followed by several washings with abundant distilled water. Finally, 15 mL of 10 mg/mL Pectolyase Y-23 solution or 25 mL of 0.5 mg/mL of purified yeast PG solution, both buffered at pH 6.0, were added and left to react for 2 h at 25 C. y-alumina spheres were then washed with 450 mL of distilled water. The reaction solution was tested for protein content and enzymatic activities. 

As mentioned above, Met(0) must be converted to Met before it can be incorporated into proteins. There are a wide variety of organisms that have been shown to be capable of enzymatically reducing Met(O) residues. The enzymatic reduction of free Met(O) to Met has been observed in yeast , E. cofi - , Pseudomonas , plants and animal tissues . The enzyme from E. coli has been purified about 1100-fold using a newly developed very sensitive assay . The assay involves first the conversion of [ S]Met(0) to [ S]Met by the Met(O) reductase followed by the measurement of [ S]Met-tRNA after enzymatic acylation of tRNA. Since Met(O) is not a substrate for the acylation reaction , the amount of [ S]Met-tRNA formed is proportional to the amount of [ S]Met(0) converted to [ S]Met. The assay is sensitive to Met levels of less than 1 pmol. 

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