Scavenger-chelator

Over the years, scientists have used many types of antioxidants in a variety of foods to retard or inhibit lipid oxidation and, thus, increase shelf-life and preserve quality. These antioxidants include free radical scavengers, chelators, and oxygen absorbers. While there are numerous antioxidants available to food scientists, the objective of this report was to discuss several of these antioxidants as they relate to meat flavor quality research and to show how they were used to retard lipid oxidation and prevent meat flavor deterioration in ground beef patties. 

Complete removal of zinc and thus inactivation of the enzyme can be accomplished in these systems at low D-PEN concentrations if a secondary scavenger chelator is added to the system. Such chelators bind metal that has been released from the enzyme but do not participate in the release.In the case of carboxypeptidase A, aM thionein (apo-metallothionen see Metallothioneins) inhibits catalysis by only about 10% over a 15-min period consistent with its action as a secondary chelator. However, in the presence of 250 aM D-PEN and aM thionein total inhibition is achieved in less than 15 min. D-PEN accelerates zinc equilibration between carboxypeptidase A and thionein (Scheme 1). This is accomplished by D-PEN catalyzing the release of Zn from the enzyme. Since D-PEN is in vast excess over both the enzyme and thionein, the enzyme-released zinc would be expected to bind to D-PEN first. However, since thionein binds zinc more tightly than D-penicillamine and can accept 7 moles of zinc per mole of thionein, it should be the ultimate acceptor of the released zinc. 

Antioxidant effect of methanol, chloroform and petrol ether extracts from the lichen Toninia Candida was assayed for their antioxidant activity by Manojlovic et al. (2012). The lichen extracts showed comparable and strong antioxidant activity and exhibited higher DPPH and hydroxyl radical scavenging, chelating activity and inhibitory activity towards lipid peroxidation. 

In tracheal explants, the basal level of amosite asbestos uptake can be decreased by adding catalase, a scavenger of hydrogen peroxide, to the dust suspension, or by preincubating the dust with the iron chelator, deferoxamine (124), a chelator that prevents the reaction of iron with hydrogen peroxide to form a hydroxyl radical (6). The decreases in particle uptake are scavenger-chelator dose-dependent, but uptake cannot be reduced below about one-third to one-half the basal level (124). Conversely, uptake can be increased if amosite asbestos or titanium dioxide particles are preincubated with iron salt solutions to increase surface iron before they are applied to the explants (125). 

Certain types of oxygen scavenger have additional functions, such as pH neutralizing and metal chelating effects. 

Lebedev, A.V., Ivanova, M.V., and Levitsky, D.O., Echinochrome, a naturally occurring iron chelator and free radical scavenger in artificial and natural membrane systems. Life Sci., 76, 863, 2005. 

The efficient removal of O2 and H2O2 vvill diminish OH formation and therefore antioxidant defence systems have evolved to limit their accumulation. Enzymic and low molecular weight antioxidants exist to scavenge free radicals as self-protection mechanisms. Some proteins exhibit antioxidant properties because they chelate transition-metal catalysts. The significance of antioxidants in relation to inflammatory joint disease is discussed below. 

Lipid peroxidation (see Fig. 17.2) is a chain reaction that can be attacked in many ways. The chain reaction can be inhibited by use of radical scavengers (chain termination). Initiation of the chain reaction can be blocked by either inhibiting synthesis. of reactive oxygen species (ROS) or by use of antioxidant enzymes like superoxide dismutase (SOD), complexes of SOD and catalase. Finally, agents that chelate iron can remove free iron and thus reduce Flaber-Weiss-mediated iron/oxygen injury. 

The chromium-catalyzed coupling is extended to the intramolecular cycli-zation to the dials 43. The O-chelating silyl scavenger is used to control the stereoselectivity as shown in Scheme 25 [61,62]. The ring size effect on the stereoselectivity is also investigated. 

In an attempt to scavenge pure oxygen directly from seawater, Aquanautics Corp. [26] has developed a process similar to that of Roberts. In the Aquanautics scheme, the solution containing the carrier (in this case, a linear pentadentade polyalkylamine chelate of Fe or Co) flows through both anode and cathode of the electrochemical cell. 

A common form of EDTA used as a preservative is calcium disodium EDTA (CaNa2EDTA). What metals will this form of the sequestrant scavenge effectively The dissolution of the solid will yield calcium ions, sodium ions, and the EDTA anion. Any metal more effectively complexed than calcium will be readily scavenged, including all ions listed in Table 9.1 except silver (Ag+) and magnesium (Mg2+). (In the absence of the calcium counterion, as in the case of the acid form of EDTA, chelation of calcium in the body can occur. In fact, EDTA administered orally is an FDA-approved treatment for calcium deposits in the bloodstream that lead to cardiovascular disease.) Citric acid (Fig. 9.3.3) is another sequestrant of metal ions in foodstuffs. 

Comparison of Free Radical Scavenging and Chelating Activities... 

Synergistic Interaction of Antioxidants, Free Radical Scavengers, and Chelators... 

RE Pliss, VA Machtin, EM Pliss. In Abstracts of Conference Regulation of Biological Processes by Free Radicals Role of Antioxidants, Free Radical Scavengers, and Chelators. Moscow, Yaroslavl, Yaroslavl State Technical University, 1998, p 17. 

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