This paper focuses on the changes of physicochemical properties and gel-forming ability of duck myofibrillar proteins (DMPs) induced using hydroxyl radical oxidizing systems. DMPs were firstly extracted and then oxidized at various H2O2 concentrations (0, 4, 8, and 12 mmol/L) using Fenton reagent (Fe3+-Vc-H2O2) to generate hydroxyl radicals, and the effects of hydroxyl radical oxidation on the physicochemical changes and heat-induced gel-forming capacity of DMPs were analyzed. We observed obvious increases in the carbonyl content (p < 0.05) and surface hydrophobicity of DMPs with increasing of H2O2 concentrations (0–12 mmol/L). In contrast, the free thiol content (p < 0.05) and water retention ability of DMPs decreased with increasing H2O2 concentrations (0–12 mmol/L). These physicochemical changes suggested that high concentrations of hydroxyl radicals significantly altered the biochemical structure of DMPs, which was not conducive to the formation of a gel mesh structure. Furthermore, the gel properties were reduced based on the significant decrease in the water holding capacity (p < 0.05) and increased transformation of immobilized water of the heat-induced gel to free water (p < 0.05). With the increase of H2O2 concentrations, secondary structure of proteins analysis results indicated α-helix content decreased significantly (p < 0.05), however, random coil content increased (p < 0.05). And more cross-linked myosin heavy chains were detected at higher H2O2 concentrations groups through immunoblot analysis (p < 0.05). Therefore, as H2O2 concentrations increased, the gel mesh structure became loose and porous, and the storage modulus and loss modulus values also decreased during heating. These results demonstrated that excessive oxidation led to explicit cross-linking of DMPs, which negatively affected the gel-forming ability of DMPs. Hence, when processing duck meat products, the oxidation level of meat gel products should be controlled, or suitable antioxidants should be added.
In this paper, we propose a mixed Jacobi-Fourier spectral method for solving the Fisher equation in a disc. Some mixed Jacobi-Fourier approximation results are established, which play important roles in numerical simulation of various problems defined in a disc. We use the generalized Jacobi approximation to simulate the singularity of solution at the regional center. This also simplifies the theoretical analysis and provides a sparse system. The stability and convergence of the proposed scheme are proved. Numerical results demonstrate the efficiency of this new algorithm and coincide well with the theoretical analysis.
The distribution of 3 H -azido-3 H -deoxythymidine (AZT, zidovudine), an antiviral drug used in the treatment of human immunode®ciency virus, was investigated in gestation day-20 (G-20) fetuses and in postnatal day-20 (PND-20) rats. At both ages, a single dose of 150 mg/kg (1.78 mmol/kg) AZT was administered orally along with tracer amounts of 14 C-AZT, and rats were randomly killed at 15, 30, 60, 120, or 240 min after dosing. The fetuses, brains, and spinal cords were processed for autoradiography. The peak concentrations of AZT in plasma of G-20 and PND-20 rats were 92.2 mg/mL (0.345 mmol/mL) and 56.6 mg/mL (0.21 mmol/mL) at 15 and 30 min after intubation, respectively. The peak concentration of fetal tissue occurred in the colon at 60 min and was 205.8 mg/g tissue. In the G-20 rats, the brain showed higher levels of AZT than spinal cord only at the 30-min sample time, whereas in the PND-20 rats, greater radioactivity was found in the spinal cord up to the 240-min sample time. This pattern of AZT distribution in the central nervous system may hypothetically be attributed to the postnatal development of an organic anion carrier system believed to be responsible for transporting AZT from the brain to the blood, resulting in relatively greater overall exposure of the spinal cord to AZT than observed in the brain. ß
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