• Polymer(Korea)
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• v.37 no.1
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• pp.5-14
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• 2013

In this paper the effect of UV (ultraviolet) exposure on HDPE (high density polyethylene)-smooth and f-PP (flexible polypropylene) geomembranes is evaluated under UVB-313 (ultraviolet wavelength 290-315 nm) exposure. Tensile property, melt flow index (MFI), oxidation induction time (OIT), both standard-OIT and high pressure-OIT and Fourier transform infrared spectroscopy/attenuated total reflectance (FTIR/ATR) results are discussed. Although tensile properties of the exposed geomembrane samples remained unchanged, the depletion of antioxidants was found higher for f-PP than for HDPE geomembrane. Arrhenius model by extrapolation was used on the data to predict the antioxidant lifetime to a typical site temperature of $20^{\circ}C$. There was no significant difference between the MFI value of the virgin and UV exposed HDPE geomembrane samples but a decrease in MFI was found in f-PP geomembrane that signifies that crosslinking has occurred. From FTIR spectra, the small peak (near $1750\;cm^{-1}$) observed in the spectrum of UV exposed sample corresponds to a carbonyl (C=O) linkage, which suggests that oxidation has occurred in the polymer structure, and another new band for f-PP between 3100 and $3500\;cm^{-1}$ is attributed to a hydroxyl bond and/or hydroperoxide bond.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.4
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• pp.594-598
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• 1998

In this study oxidative deterioration of dried sea mussel and baby clam stored at $4{\pm}2^{\circ}C$ and $25{\pm}2^{\circ}C$ were investigated. Acid value of samples were higher at $25^{\circ}C$ than those at $4^{\circ}C$ throughout the storage period. And it was higher in dried baby clam than in sea mussel regardless of storage temperatures. Peroxide value of dried sea mussel and baby clam stored at $25^{\circ}C$ tended to decrease after 30 and 60 days, respectively. Thiobarbituric acid and carbonyl value of samples stored at $4^{\circ}C$ were higher than those stored at $25^{\circ}C$ throughout the storage period. In case of sea mussel, However they were lower stored at $4^{\circ}C$ than at $25^{\circ}C$ in 30 days. Amino nitrogen increased until 60 days and then decreased in all samples. Fluorescence intensity associated with interaction between carbonyl compound and amino compound was increased with storage temperature and time but it decreased slowly after 60 days.

• Proceedings of the Plant Resources Society of Korea Conference
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• v.18 no.1
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• pp.52-60
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• 2005

The objectives of present study were to investigate the hepatoprotective and antioxidative effects of onion extracts. Primary cultures of rat hepatocytes were incubated with 1.5 mM tert-butyl hydroperoxide(t-BHP), potent oxidizing agent for liver injury for 1 hr in the presence or absence of various concentrations (0, 0.01, 0.05, 0.1 or 0.3 mg/ml) of onion extract. Cytotoxicity and cell viability were determined by measuring glutamic oxaloacetic transaminase(GOT) activity, lactate dehydrogenase(LDH) activity and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide(MTT) value. Lipid peroxidation was evaluated using thiobarbituric acid reactive substances(TBARS) assay. Effects on antioxidant system were determined by measuring catalase, glutathione peroxidase(GSH-Px), glutathione reductase(GSH-Rd) activities as well as DNA strand breaking assay. Incubation with t-BHP alone increased GOT and LDH activities and TBARS concentration but decreased MTT reduction. Onion extracts at the concentration of 0.05 mg/ml began to decrease GOT and LDH activities induced by 1.5 mM t-BHP. Decreased MTT reduction began to be increased by onion extract at the concentration of 0.01 mg/ml. Onion extracts at the concentration of 0.01 mg/ml began to decrease TBARS concentration induced by t-BHP. Taken together, onion extracts prevented t-BHP-induced hepatocyte injury and lipid peroxidation. Catalase, GSH-Px and GSH-Rd activities of hepatocytes were significantly decreased by 1.5 mM t-BHP for 1 hr incubation. Onion extracts, on the other hand, at the concentration of 0.1 mg/ml began to prevent t-BHP-induced decrease in catalase, GSH-Px and GSH-Rd activities. Onion extracts prevented hydroxyl radical-induced single-strand breakage in dose-dependent manner when plasmid DNA was incubated with various concentrations of onion extracts in the presence of Fenton regents producing hydroxyl radical. These results demonstrate that onion extracts suppressed t-BHP-induced cytoctoxicity, decreased viability and lipid peroxidation and increased GSH-Px, GSH-Rd and catalase activities. Thus hepatoprotective and antioxidant effects of onion extract seem to be due to, at least in part, the increase in antioxidant enzyme activities as well as prevention from hydroxyl radical-induced oxidation, followed by inhibition in lipid peroxidation.

• Journal of the Korean Society of Food Science and Nutrition
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• v.42 no.6
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• pp.933-940
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• 2013

In this study, methyl esters with different saturated fatty acids (SFA) were prepared by urea fractionation to make an oil-in-water emulsion. Emulsion characteristics (emulsion stability and oxidative stability) of the methyl ester emulsion were then studied at different percentages of methyl ester saturation (5, 28, 39, 50, and 72%, termed ${\Sigma}$SFA5, ${\Sigma}$SFA28, ${\Sigma}$SFA39, ${\Sigma}$SFA50, and ${\Sigma}$SFA72, respectively). The stability of emulsions (ES) with different SFA content was 46.0 (${\Sigma}$SFA5), 39.5 (${\Sigma}$SFA28), 32.7 (${\Sigma}$SFA39), 32.6 (${\Sigma}$SFA50), and 27.3 (${\Sigma}$SFA72). Results from Turbiscan showed that creaming or clarification, based on the backscattering intensity, was more pronounced with increases in the saturation degree of the emulsion. These results implied that the emulsions with lower saturation were more stable. During 30 days of storage, the lipid peroxide value increased for all emulsions, with the increase less pronounced with the increasing saturation of the emulsion; 1.880 (${\Sigma}$ SFA5), 1.267 (${\Sigma}$SFA28), 1.062 (${\Sigma}$SFA39), 0.342 (${\Sigma}$SFA50) and 0.153 (${\Sigma}$SFA72) mg $H_2O_2/mL$ emulsion. In addition, thiobarbituric acid reactive substances (TBARS) values were significantly lower in emulsions with high saturation (4.419 mg for ${\Sigma}$SFA50 and 4.226 mg for ${\Sigma}$SFA72) than emulsions with low saturation (6.229 mg for ${\Sigma}$SFA5, 6.801 mg for ${\Sigma}$SFA28 and 6.246 mg for ${\Sigma}$SFA39). In conclusion, the emulsions with a higher saturation degree of methyl esters showed lower emulsion stability but better oxidation stability.