Oxidase enzymes enzymatic

SO2 is not only antimicrobially active, but inhibits discoloration by blocking compounds with a reactive carbonyl group (Maillard reaction nonenzymatic browning) or by inhibiting oxidation of phenols by phenol oxidase enzymes (enzymatic browning). 

Many enzymatic assays have also been developed for the analysis of proteolytic products. Total amino acids in Cheddar cheese were determined by Puchades et al. (1990) using the L-amino acid oxidase enzyme. Glutamic acid has been quantified by flow injection analysis using glutamate dehydrogenase (Puchades et al., 1989) and using the Boehringer-Mannheim kit (McSweeney et al., 1993). 

Trusov (1915,1916), as indicated in Section 1.4.1, introduced the concept that polyphenols and quinones contributed to the synthesis of HS. Subsequently, as the result of enzymatic oxidation (with oxidase enzymes from microorganisms), the phenols oxidize to quinones and these, through further condensation, are converted into dark-colored humic-type substances. 

Closed systems may be employed when buffer recycling is possible, that is when the buffer contains high concentrations of all necessary cosubstrates, when complete consumption of injected substrate occurs within the reactor, and when products of the enzymatic reaction do not inhibit the immobilized enzyme. A closed system for immobilized oxidase enzymes is shown in Figure 4.10. 

Enzymes known as polyphenol oxidases cause enzymatic browning. Other names of the enzyme include phenolases and tyrosinases. The enzymes catalyze the conversion of monophenols and diphenols to quinones. The quinones can undergo a series of non-enzymatic reactions to produce brown, gray and black colored pigments, collectively known as melanins (11). Maillard reactions, caramelizations and ascorbic acid oxidations can produce similar types of colored compounds (12). For some food processing... 

Similarly, polyphenols are synthesized by microorganisms from nonhumic substances, which are subsequently converted to quinines through enzymatic reactions. The conversion of polyphenols formed from both sources to quinines is catalyzed by oxygen-requiring phenol oxidase enzymes. Quinones polymerize with or without amino compounds to from complex humic substances (Figure 5.15b). 

The purpose of the study by Quoc et al (2006) was to develop a process to enable quick inactivation of the polyphenol oxidase enzyme, which is present in cloudy or unclarified apple juice. This enzyme is responsible for enzymatic... 

Biosensors have recently become an area of great Interest, especially in clinical chemistry. These sensors can be used to determine analyte concentrations in clinical samples, such as blood serum and urine. Electrochemical biosensors are constructed by incorporating a biochemical system, such as an enzyme, with an electrode. Amperometrlc biosensors often use oxidase enzymes, such as glucose oxidase, as the sensing enzyme. A major product of these types of enzymatic reactions is hydrogen peroxide, which can be oxidized at eun electrode surface. The current produced by the oxidation of hydrogen peroxide is directly proportional to the enzymatic substrate concentration. 

These works are based on the principle that the separation etRciency of HPLC is coupled with the specificity of amino acid oxidase enzymes and the sensitivity of ED of the hydrogen peroxide enzymatically generated. 

Some sweeteners (aspartame, cyclamate, saccharin, and acesulfame K) were determined by CE-SIA with contactless conductivity detection (Stojkovic et al., 2013). The analyses were carried out in an aqueous running buffer consisting of 150 mM 2-(cyclo-hexylamino)ethanesulfonic acid and 400 mM tris(hydroxymethyl)aminomethane at pH 9.1 in order to render all analytes in the fully deprotonated anionic form. The four compounds were determined successfully in food samples the experimental set-up and typical analysis results are illustrated in Figure 2.9. Another SIA system combined with solenoid valves was used to automate an enzymatic method for the determination of aspartame in commercial sweetener tablets. The method involves the enzymatic conversion of aspartame to hydrogen peroxide by the chymotrypsin-alcohol oxidase system, followed by the use of 2,2-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ARTS) as electron donor for peroxidase. Chymotrypsin and alcohol oxidase enzymes were immobilized on activated porous silica beads (Pena et al., 2004). 

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