The 96-well plate was loaded into the plate reader and the solution in each cell was mixed by shaking at 1200 rpm for 20 s. In a run, 100 μl of pure compounds or food extracts appropriately diluted in 75 mM phosphate buffer (pH 7.4) was transferred into reaction cells on a 96-well plate, and 100 μl of DCFH was added. ABAP (200 mM) was prepared fresh in buffer, and each batch was kept at 4 ☌ between runs. DCFH-DA was stable to oxidation, whereas DCFH was very slowly oxidized at ambient conditions without ABAP. Just before use in the reaction, 80 μl of 2.48 mM DCFH-DA was hydrolyzed with 900 μl of 1.0 mM KOH for 3–5 min in a vial to remove the diacetate (DA) moiety and then diluted to 6 ml total volume with 75 mM phosphate buffer (pH 7.4). The protocol for PSC method is performed according to the method of Adom and Liu (2005). The degree of inhibition of DCFH oxidation, by antioxidants that scavenge peroxyl radicals, was used as the basis for calculating antioxidant activity. The reaction mechanism for PSC assay is as follows: Thermal degradation of ABAP produces peroxyl radicals (ROOH) ( Pryor et al., 1993 Winston et al., 1998), which oxidize nonfluorescent DCFH to fluorescent dichlorofluorescein (DCF). PSC method is a rapid, simple, and reliable approach for measuring both hydrophilic and lipophilic antioxidant capacity of pure antioxidant compounds, food extracts, and biological fluids toward biologically relevant radicals, based on the oxidation of 2′,7′-dichlorofluorescin (DCFH) by peroxyl radicals ( Adom and Liu, 2005). Liu, in Encyclopedia of Agriculture and Food Systems, 2014 Rapid Peroxyl Radical Scavenging Capacity Scavenging may thus be limited at low temperatures because, without the chemical cues, scavengers may have difficulty finding a potentially edible carcass. Lower temperatures are less favorable for microbial activity and accordingly there is little or no production of chemical odors. Higher temperatures and associated higher rates of decomposition lead to higher concentrations of toxic amines and sulfur compounds that signal to scavengers that the item is inedible. Indeed, experimental studies have demonstrated that under such conditions scavengers can find and begin to remove carrion within minutes to hours after becoming available. At moderate temperatures (e.g., 10–15 ☌) microbial decomposition is at a level that produces modest concentration of chemicals leading to putrid odors that signal the location of edible carrion to scavengers. So, to avoid competition with scavengers, decomposers have evolved capacities to produce noxious and odorous chemicals that can make the entire carcass distasteful or even toxic. Decomposers alone are rarely able to utilize entire carcasses. This interplay leads to intermediate, optimal temperatures for scavenging, especially within temperature regions of the globe. Scavenging can be temperature dependent because of interplay between microbial decomposition and chemical detection of carcasses. Research has also shown that scavenging efficiency, defined as the proportion of a carcass that was consumed within this time frame, averages 75%, a value that rivals the efficiencies of carnivores consuming their hunted prey. Depending on the size and species of carrion, a carcass can be despatched within hours to days. Clearly, neither the Serengeti plains, nor any other location globally, is littered with dead animal carcasses, testimony to the magnitude of this trophic interaction. In the Serengeti alone, the annual amount available to scavengers is estimated to be on the order of 26 million kg. Although the exact value varies among species and sizes of prey, predation accounts for between 2% and 75% of organism losses annually, thus leaving 25–98% to be scavenged. Research has shown that many organisms die from sources other than predation. Scavengers, however, are often more efficient than decomposers at despatching carrion. Hence, scavengers compete with decomposers for carrion. In many cases, however, it is redirected to bolster populations of a diversity of scavenger species, including turkey vultures, coyotes, ravens, and foxes (denoted by thick arrow from elk carcass to scavengers and thin arrows to decomposed organic pool). Much of this abundant carrion can be broken down into constituent chemical elements by decomposers (denoted by thick arrow from elk carcass to the decomposed organic matter pool) if scavengers are absent. The remaining 25–98% of all individuals that die annual succumb to nonpredation causes. In many systems, including the example of wolves preying on elk, predation accounts for 2–75% of losses of individual prey annually (denoted by thin arrow from the elk carcass to wolves).
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