Fermentation, enzyme action

Currently, a-amino acids are prepared by several routes such as by the fermentation of glucose, by enzyme action on several substances and by the hydrolysis of proteins. Many methods for synthesising the polymers are known, of which the polymerisation of A -carboxyanhydrides is of particular interest, as it yield-products of high molecular weight (Figure 18.24). 

The self-assembly of caseins may be readily manipulated by processing methods that affect the integrity of native casein micelles and the character of the casein interactions in aqueous media. Examples of such procedures are (Dickinson, 2006) (i) acidification toward the isoelectric point (p/) (pH 4.6-4.8), leading to a neutralization of the net protein charge (ii) enzyme action, as exploited in the production of cheeses and fermented milks (iii) addition of divalent ions, especially, Ca2+ ions (iv) addition of sucrose or ethanol (v) temperature treatment and (vi) high-pressure treatment. 

Stillings and Hackler (54) studied the effects of the tempeh fermentation, the action of Rhizopus oligosporus on dehulled, soaked, and sterilized soybeans. The PER of tempeh reached its peak after 24 hours fermentation and then dropped. They ascribed the changes to an increase and then a decrease in tryptophan chemically present. The PER decrease after 24 hours was also attributed to an increased quantity of mold protein, which is lower in sulfur amino acid concentration than the original soy protein. Free amino acids increased markedly, presumably due to the action of the mold proteolytic enzymes. Free methionine was present in the largest amount, and as such was highly available, thus partially accounting for the initial increase in PER. 

Irrespective of the type of biomass used for ethanol production, the biomass needs to be pretreated to make the carbohydrates available for fermentation. However, which enzymes can be used depends on the source of the biomass. In addition, the biomass needs pretreatment before the enzymes are used. The first step of the pretreatment can be of a physical nature. Once the biomass is physically pretreated, the cellulose structures are open for enzyme action. In biomass from forests, the substance is mainly in the form of cellulose. Targeted enzymes are selective for the reaction of cellulose to glucose, and therefore there are no degradation byproducts, as occurs in acid conversion technology. There are at least three ways this can be performed. Firstly, in separate hydrolysis and fermentation, the pretreated biomass is treated with cellulase, which hydrolyzes the cellulose to glucose at 50 °C and pH 4.8. Secondly, in simultaneous fermentation and saccharification (SSF) the hydrolysis and fermentation take place in the same bioreactor. Thirdly,... 

Fresh food flavors are produced by biosynthetic enzymes in the living tissue and by degradative enzymes which begin acting when the tissue is cut or crushed. The flavors of cultured and fermented foods result from the enzyme action of the microorganisms involved. In some cases (e.g., tea fermentation) flavor results largely from nonenzymatic... 

In an experiment with 8.5 g. of amylose and malt a-amylase, the enzyme action was stopped when the degree of hydrolysis was 22.4%, that is, at the end of the dextrinization phase. Fermentable sugar was removed by fermentation (17%) and the non-fermentable a-dextrins were fractionated with alcohol. Six fractions were obtained (Table XI) having chain lengths from 4 to 10 units. 

Due to the activity of the functional fermentation nucrobiota, molecules can be formed in fermented soya foods that have been proven and/or suggested to have positive influences on human health. Folic acid or folate, and vitamin B12 or cyanocobalamin are vitamins that can be synthesized by microorganisms (Mo et al., 2013). Isofla-vones in soya are glycosides and as such, poorly accessible. By enzymic action these... 

The same decade saw the development of a modem concept of enzyme action. Fischer published his studies of the hydrolyses of the a- and )S-glycosides of d- and L-glucose in 1894 (Boyde, 1980 Teich and Needham, 1992). The active agents which he used to catalyse these reactions were the soluble ferments separated from S. cerevisiae and other microoiganisms, the so-called enzymes , as he described them, using the term which Kiihne had introduced in 1878 (Boyde, 1980). Some of these preparations catalysed a range of hydrolyses which do, in fact, reflect the action of several enzymes (Boyde, 1980) nevertheless, their specifications were sufiiciently clear cut to allow him to propose... 

Mannitol. Whereas mannitic fermentations are seldom a problem where sulfur dioxide, pure yeasts, and temperature control are employed, Martucci (1941) has reported them in Argentina. He recommended control of the must acidity, since a high pH also favored such spoilage. A complicated polaiimetric procedure for mannitol (a sugar alcohol) in wines was presented by Salani (1937). Formation of mannite during dialysis of musts at low temperatures (8° to 10° C. (46.4° to 50° F.)) in the presence of chloroform was reported by Barbera (1933b) (possibly owing to enzyme action). 

Enzymes are substances formed by living organisms that have catalytic power that is, the power to increase the rate of certain chemical reactions. Enzyme action is involved in the processes of fermentation in the preparation of wine, vinegar, beer, and bread, which have been known... 

Direct determinations of the adsorption of ethylene on egg albumin, urease, sodium oleate, and other sols have been made by Nord and his associates (Ola). These show that only in the case of the sodium oleate is tlic adsorption conspicuous, although they do not completely exclude adsorption on egg albumin, or on untested cellular enzymes. The indirect evidence from the increase in surface tension and the decrease in viscosity of colloids produced by ethylene suggests that adsorption occurs. But ethylene is considered not to show resonance (69a), a prerequisite for the presence of the polarized form suggested by Nord and Franke (63a, 63b) as the basis for its adsorption. It seems still undecided whether or not ethylene is adsorbed at strategic positions on any of the cellular fermentation enzymes. The increased carbon dioxide production in the presence of an ethylene film is well established by Nord et al. (62a, 62b, 63, 63a, 63b) but there is less evidence as to the manner of action of ethylene. 

In enzymes, this folding process is crucial to their activity as catalysts, with part of the structure as the center of reactivity. Heating enzymes (or other treatments) destroys their three-dimensional structure so stops further action. For example, in winemaking, the rising alcohol content eventually denatures the enzymes responsible for turning sugar into alcohol, and fermentation stops. 

The term fermentation was obtained from the Latin verb fervere which describes the action of yeast or malt on sugar or fruit extracts and grain. The boiling is due to the production of carbon dioxide bubbles from the aqueous phase under the anaerobic catabolism of carbohydrates in the fermentation media. The art of fermentation is defined as the chemical transformation of organic compounds with the aid of enzymes. The ability of yeast to make alcohol was known to the Babylonians and Sumerians before 6000 bc. The Egyptians discovered the generation of carbon dioxide by brewer s yeast in the preparation... 

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