The
main purpose of this study was to investigate the effects of
oxidation in vitro on the biochemical properties
of myofibrillar protein isolates (MPIs) from beef muscles. MPIs were
incubated at 4 °C for 24 h with hydroxyl-radical-generating systems
consisting of 0.01 mM FeCl3 and 0.1 mM ascorbic acid plus
0, 0.2, 1, 5, 10, and 20 mM hydrogen peroxide. The results showed
that oxidation caused drastically structural changes in bovine MPIs.
The carbonyl content, the surface hydrophobicity, and the particle
diameter of MPIs were significantly increased, while the free sulfhydryl
group content was dramatically decreased with increasing hydrogen
peroxide concentrations. Oxidation caused the protein aggregations
through cross-linking between proteins and amino acids. Proteomics
study identified protein sites in which they were easy to be oxidized.
Oxidized catalytic activities and binding sites of enzymes that were
susceptible to oxidation were also identified.
To
achieve high efficiency and low consumption for water treatment
in the Fenton reaction, we use the surface oxygen vacancies (OVs)
as the electron temporary residences to construct a dual-reaction-center
(RDC) Fenton-like catalyst with abundant surface electron-rich/poor
areas consisting of OV-rich Co-ZnO microparticles (OV-CoZnO MPs).
The lattice-doping of Co into ZnO wurtzite results in the formation
of OVs with unpaired electrons (electron-rich OVs) and electron-deficient
Co3+ sites according to the structural and electronic characterizations.
Both experimental and theoretical calculations prove that the electron-rich
OVs are responsible for the capture and reduction of H2O2 to generate hydroxyl radicals, which quickly degrades
pollutants, while a large amount of pollutants are adsorbed at the
electron-deficient Co3+ sites and act as electron donors
for the system, accompanied by their own oxidative degradation. The
electrons obtained from the pollutants in the electron-deficient sites
are transferred to the OVs through the internal bond bridge to achieve
the balance of electron gain/loss. Through this process, pollutants
are efficiently converted and degraded by multiple pathways in a wide
range of pH (4.5–9.5). The reaction rate of the OV-CoZnO MPs/H2O2 system is increased by ∼17 times compared
with the non-DRC system. This discovery provides a sustainable strategy
for pollutant utilization, which shows new implications for solving
the troublesome issues of the Fenton reaction and for developing novel
environmental remediation technologies.
A popular hypothesis for the noted steady decline in the population of Steller sea lions, Eumetopias jubatus (Schreber, 1776), in the regions from Prince William Sound through the Aleutian Islands relates to their nutritional status. Sea lion diets appear to have shifted from primarily small schooling fatty fishes to low-fat fish such as walleye pollock, Theragra chalcogramma (Pallas, 1814). We examined the seasonal changes in proximate nutrients of pollock collected in the Bering Sea. Mean energy density (dry mass) of pollock peaked in October then declined and remained low throughout winter. Energy recovery occurred in the summer months with strong recovery observed in female fish caught in July. Contrary to whole fish carcass energy contents, both total protein and moisture contents were at their highest levels in winter (January) when total crude lipid content was at its lowest (p < 0.05). This trend gradually declined to its lowest levels in the fall when lipid content was high. The decline in total lipids during winter seasons appeared to parallel gonad development during the prespawning period. Sex differences in energy densities were not found. Proximate analysis data for moisture, protein, ash, and lipid content also did not show any significant variation between males and females. Protein digestibility of pollock was higher (p < 0.05) in the summer than in the spring, but not different for winter or fall. We concluded that the nutrient content of walleye pollock may have some impact on the Steller sea lions that feed on them, particularly the energetic value that appears to be low during important feeding periods for this marine mammal.
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