Enzymes process conditions

With respect to the action of the enzyme itself, a loss of weight on account of cellulose hydrolysis, as well as loss in strength properties, occurs. Therefore, control of concentrations, temperature, and other processing conditions is important to achieve a product having the proper balance of properties. 

The susceptibility of biological systems, including procaryotic and eucaryo-tic cultures and enzyme solutions, to the forces prevailing under normal processing conditions has been extensively studied and is the subject of comprehensive reviews [12-16], including other chapters in this volume. Downstream processing operations, as well as routine pumping, will expose cell suspensions... 

Compared with ketoreductases, the synthetic application of alcohol oxidases has been less explored. However, selective oxidation of primary alcohols to aldehydes is superior to the chemical methods in terms of conversion yields, selectivity, and environmental friendliness of reaction conditions. In addition, coupling of alcohol oxidase with other enzymes provides a tremendous opportunity to develop multi-enzyme processes for the production of complex molecules. Therefore, a growing impact of alcohol oxidases on synthetic organic chemistry is expected in the coming years. 

In general, biomolecules such as proteins and enzymes display sophisticated recognition abilities but their commercial viability is often hampered by their fragile structure and lack of long term stability under processing conditions [69]. These problems can be partially overcome by immobilization of the biomolecules on various supports, which provide enhanced stability, repetitive and continuous use, potential modulation of catalytic properties, and prevention of microbial contaminations. Sol-gel and synthetic polymer-based routes for biomolecule encapsulation have been studied extensively and are now well established [70-72]. Current research is also concerned with improving the stability of the immobilized biomolecules, notably enzymes, to increase the scope for exploitation in various... 

In a lipase-catalyzed reaction, the acyl group of the ester is transferred to the hydroxyl group of the serine residue to form the acylated enzyme. The acyl group is then transferred to an external nucleophile with the return of the enzyme to its preacylated state to restart the catalytic cycle. A variety of nucleophiles can participate in this process. For example, reaction in the presence of water results in hydrolysis, reaction in alcohol results in esterification or transesterification, and reaction in amine results in amination. Kirchner et al.3 reported that it was possible to use hydrolytic enzymes under conditions of limited moisture to catalyze the formation of esters, and this is now becoming very popular for the resolution of alcohols.4... 

Cost sensitivity studies have shown that the successful commercialization of cellulase-based processes, such as the conversion of cellulose to fermentable sugars, is highly dependent on the cost of enzyme production (i). Because fungal -D-glucosidase (EC 3.2.1.21) is the most labile enzyme in this system under process conditions (2), and k to efficient saccharification of cellulose, this enzyme was targeted for application of stabilization technology, both through chemical modification and immobilization to solid supports. 

In the design of coatings, hydrogels and matrices based on azo polymers, the number of azo bonds in the polymers should not be too high, as this could lead to enzyme-saturated conditions slowing down the degradation process and thus drug release [72]. 

The optimization of enzymes strongly depends on the field of appHcation. For industrial applications, high reaction rates, stabiHty under process conditions, and regio- and enantioselectivity are the most important properties of a catalyst, whereas affinity or substrate selectivity are of second order interest for a distinct process to be catalyzed. On the other hand, enzymes with a wide range of activity can be used for the production of several products reducing... 

Dekker et al. [170] have also shown that the steady state experimental data of the extraction and the observed dynamic behavior of the extraction are in good agreement with the model predictions. This model offers the opportunity to predict the effect of changes, both in the process conditions (effect of residence time and mass transfer coefficient) and in the composition of the aqueous and reverse micellar phase (effect of inactivation rate constant and distribution coefficient) on the extraction efficiency. A shorter residence time in the extractors, in combination with an increase in mass transfer rate, will give improvement in the yield of active enzyme in the second aqueous phase and will further reduce the surfactant loss. They have suggested that the use of centrifugal separators or extractors might be valuable in this respect. 

Prior to fermentation, the wort is then cooled to temperatures below 85°F (30°C), and the pH is adjusted to about 5. Yeast such as Saccharomyces cerevisiae, Saccharomyces carlsbergensis or Candida brassicae are added and fermentation proceeds for 2 to 3 days under batch processing conditions. Yeast produces the enzymes maltase, zymase, and invertase. Maltase converts maltose to glucose. Zymase converts glucose to ethanol. Invertase converts any sucrose present to fermentable sugar. The following equations illustrate the enzymatic conversion of starch to ethanol ... 

Aliphatic ethers with branched side chains such as MTBE (methyl t-butyl ether), especially, deactivate enzymes only to a very small degree in incubation experiments for example, the BAL mentioned above has a half-life h/2 of up to 500 h in aqueous-organic two-phase systems (see Fig. 3.1.6) [21]. This may not hold true for a special enzyme/solvent combination under process conditions. When incubated at higher temperatures or even in the presence of the substrate benzaldehyde the deactivation of the enzyme is much higher (see Table 3.1.2)... 

Many attempts have been made to correlate the enantioselective properties of enzymes with structure and/or process conditions [61, 70-73]. Attempts to correlate the effect of a particular medium on the enantioselectivity of an enzyme-catalyzed reaction with physico-chemical descriptors of the solvent have also been reported by a number of groups [22, 59, 64, 74]. Correlations with solvent size [75], dielectric constant [59], polarizability, electron pair acceptance index [76], logP [17],... 

A comparison of the qualitative results of the two mathematical models shows strong similarities between the consequences of the mass transfer limitation model and the adsorbed enzyme model [28]. Experimental findings show that the reaction mode is strongly dependent on the process conditions, and the different models cannot be adopted for other conditions [29]. 

The following factors appear to control the emulsification properties of milk proteins in food product applications 1) the physico-chemical state of the proteins as influenced by pH, Ca and other polyvalent ions, denaturation, aggregation, enzyme modification, and conditions used to produce the emulsion 2) composition and processing conditions with respect to lipid-protein ratio, chemical emulsifiers, physical state of the fat phase, ionic activities, pH, and viscosity of the dispersion phase surrounding the fat globules and 3) the sequence and process for incorporating the respective components of the emulsion and for forming the emulsion. 

This Chapter is essentially in two parts. In Sections S.2 to S.7 is included the basic microbiology and biochemistry of cells and enzymes and the reactions which they can undergo or catalyse. This is followed by a disccussion of the utilisation of biological reactions under industrial process conditions—Sections 5.8 to 5.14. 

Enzyme techniques are primarily developed for commercial reasons, and so information about immobilization and process conditions is usually limited. A commercially available immobilized penicillin V acylase is made by glutaraldehyde cross-linking of a cell homogenate. It can be used in batch stirred tank or recycled packed-bed reactors with typical operating parameters as indicated in Table 2 (38). Further development may lead to the creation of acylases and processes that can also be used for attaching side chains by enzymatic synthesis. 

Therefore tailoring the enzyme to the processing conditions would be preferred recent advances in random mutagenesis and directed evolution, notable features conceptually illustrated in Figure 11.3, offer the possibility of achieving this goal in the absence of detailed structural information on the protein. 

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