• Applied Biological Chemistry
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• v.41 no.4
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• pp.241-245
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• 1998

Two oxidation states of chromium commonly occur in natural soil/water systems, Cr(III) and Cr(VI). The oxidized form, Cr(VI), exists as the chromate ion and is more mobile and toxic than Cr(III). Therefore oxidation of Cr(III) by various Mn-oxides in natural systems is a very important environmental concern. Organic substances can inhibit the Cr(III) oxidation by binding, Cr(III) strongly and also by dissolving Mn-oxides. Most of Cr(III) oxidation studies were carried out using in vitro systems without organic substances which exist in natural soil/water systems. In this study effect of organic acids - oxalate and pyruvate - on Cr(III) oxidation by $birnessite({\delta}-MnO_2)$ was examined. The two organic acids significantly inhibited Cr(III) oxidation by birnessite. Oxalate showed more significant inhibition than pyruvate. As solution pH was lowered in the range of 3.0 to 5.0, the Cr(III) oxidation was more strongly depressed. Addition of more organic acids reduced the Cr(III) oxidation mare extensively. Different inhibition effects by the organic acids could be due to their ability of reductive dissolution of Mn-oxides and/or Cr(III) binding. Organic acids dissolved Mn-oxide during the Cr(III) oxidation by the oxide, Dissolution by oxalic acid was much greater than that by pyruvate, and the dissolution was more extensive at lower pH. Inhibition of Cr(III) oxidation was parallel to the dissolution of Mn-oxide by organic acids. Although the effect of Cr(III) binding by organic acids on Cr(III) oxidation is not known yet, Mn-oxide dissolution by organic acids could be a main reason for the inhibition of Cr(III) oxidation by Mn-oxide in presence of organic acids. Thus oxidation of Cr(III) to Cr(VI) by various Mn-oxides in natural systems could be much less than the oxidation estimated by in vitro studies with only Cr(III) and Mn-oxides.

• The Korean Journal of Food And Nutrition
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• v.8 no.2
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• pp.135-144
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• 1995

Lipid oxidation in foods produce the peroxidation products, toxic substance and rancidity odor. In vivo, lipid peroxidation by free radicals or molecular singlet oxygen cause such as a damage of DNA, cancer and aging. Accordingly, the development of new compound Inhibit lipid oxidation in foods and in vivo is very important. Antioxidants are generally used as a protection material of oxidation for a storage and preservation of foods. In terms of stability of foods and health for human, development of high effective antioxidants In a nature is required. In this point of view, this paper presents the research trends of a kind of natural antioxidative substances and its antioxidative activity.

• Journal of the Korean Applied Science and Technology
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• v.6 no.1
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• pp.9-14
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• 1989

Effectiveness of some natural antioxidants were investigated by measuring the physico-chemical charcteristics and fatty acid composition during thermal oxidation in palm oil. Tocopherol showed most enhanced thermal oxidation stabilities compared to the other natural antioxidants. AR spice was no good AOM stability and changes of acid value but the other parameters were obtained desirable results. The changes of linoleic aicd content was slightly decreased during thermal oxidation. Addition of rosemary and glycyrriza extract increased the stabilities of oil less than tocopherol and AR spice. Order of antioxdative effects was tocopherol, AR spice and others. There was no significiant difference in stability of rosemary and glycyrriza extract.

• Bulletin of the Korean Chemical Society
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• v.29 no.12
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• pp.2513-2516
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• 2008

• YAKHAK HOEJI
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• v.17 no.3
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• pp.123-128
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• 1973

Panax Saponin A (isopropyl-$^{14}C$) was prepared from natural saponin in good yield by the precesses; acetylation, osmium tetroxide oxidation, periodic acid oxidation, Witting process, and saponification.

• Journal of Animal Science and Technology
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• v.65 no.1
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• pp.225-243
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• 2023

Large amounts of additives are used during meat product processing to maintain product quality and shelf life. With the growing interest in healthy foods, natural plant-based additives are being used as alternatives to synthetic additives. In this study, six types of natural extracts with excellent antibacterial activity were selected, and their antibacterial and antioxidant activities against four types of pathogens were evaluated in various combinations. In addition, the pH, color, amount of thiobarbituric acid reactive substances (TBARS), and growth of pathogenic microorganisms were analyzed during the storage of sausages treated with various combinations of these extracts. The natural extract mixtures exhibited different antibacterial activities, depending on the combination. Compared to grapefruit seed extract, a mixture of natural extracts extracted with ethanol (M4) reduced the Escherichia coli content by more than 99.9% after 8 days of storage and slowed the growth of Listeria monocytogenes and Salmonella spp. by more than 80% after 14 days. Compared to untreated (NC) and grapefruit extract (PC)-treated sausages, sausages treated with the natural extract mixtures showed a significant decrease in CIE L^* and an increase in CIE a^* and CIE b^* (p < 0.05). The pH value was significantly lower in sausages containing natural extract mixtures than in the NC and PC sausages (p < 0.05). The natural plant extract mixtures significantly prevented lipid oxidation (p < 0.05). In summary, different types of natural extract mixtures have a synergistic effect when used together, suggesting that natural preservatives can generally inhibit the growth of microorganisms and oxidation of processed meat.

• Elastomers and Composites
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• v.55 no.1
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• pp.51-58
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• 2020

In this study, the thermal oxidation of raw natural rubber (NR) was investigated under controlled conditions by optical image and fourier transform infrared (FT-IR) analysis. The thermal oxidation was performed on a transparent thin film of raw NR coated on a KBr window in a dark chamber at 80℃ under low humidity conditions to completely exclude moisture and restrict light oxidation. Images of the thin film of raw NR were obtained before and after thermal oxidation. FT-IR absorption spectra were measured in the transmission mode at different thermal exposure times. The thermal oxidation of NR was examined by the changes in the absorption peaks at 3449, 1736, 1447, 1377, 1242, 1072, and 833 cm^-1, which corresponded to a hydroxyl group (-OH), a carbonyl group (-C=O) from an aldehyde and a ketone, a methylene group (-CH₂-), a methyl group (-CH₃), a carbon-oxygen single bond (-C-O) from an epoxide, a carbon-oxygen bond (-C-O) from an ether, an alcohol, a peroxide, or a cyclic peroxide, and a cis-methine group (cis-CCH₃=CH-), respectively. In the initial stage of thermal oxidation, two different types of free radicals were produced quickly and randomly by the homolytic cleavage of a double bond and allylic hydrogen abstraction. Aldehydes and ketones were formed from chain scissions of the double bonds and alcohols were produced from allylic hydrogen abstraction at the methylene or methyl groups. Two reactions seemed to proceed competitively with each other. At a later stage, oxidative crosslinks seemed to dominate through the combination of free radicals such as an allyl radical (CH=CHCH₂·), alkoxy radical (RO·), and peroxy radical (ROO·) and the reaction of a hydroperoxide (-ROOH) with a double bond. The image obtained after thermal oxidation showed hardening without cracks. Based on these observations, a plausible two-step mechanism was suggested for chain hardening caused by the thermal oxidation.

• Elastomers and Composites
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• v.51 no.1
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• pp.1-9
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• 2016

Characterization of the UV oxidation for raw natural rubber (NR) was investigated in controlled conditions through image and FT-IR analysis. The UV oxidation was performed on a thin film of natural rubber coated on a KBr window at 254 nm and room temperature to exclude the thermal oxidation. Before or after exposure to UV light, image of the NR thin film was observed at a right or tilted angle. FT-IR absorption spectra were measured in transmission mode with the UV irradiation time. The UV oxidation of NR was examined by the changes of absorption peaks at 3425, 1717, 1084, 1477, 1377, and $833cm^{-1}$ which were assigned to hydroxyl group (-OH), carbonyl group (-C=O), carbon-oxygen bond (-C-O), methylene group $(-CH_2-)$, methyl group $(-CH_3)$, and cis-methine group $(cis-CCH_3=CH-)$, respectively. During the initial exposure period, the results indicated that the appearance of carbonyl group was directly related to the reduction of cis-methine group containing carbon-carbon double bond (-C=C-). Most of aldehydes or ketones from carbon-carbon double bonds were formed very fast by chain scission. A lot of long wide cracks with one orientation at regular intervals which resulted in consecutive chain scission were observed by image analysis. During all exposure periods, on the other hand, it was considered that the continuous increment of hydroxyl and carbonyl group was closely related to the decrement of methylene and methyl group in the allylic position. Therefore, two possible mechanisms for the UV oxidation of NR were suggested.

• Journal of the Mineralogical Society of Korea
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• v.27 no.4
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• pp.223-233
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• 2014

Cyanidation method has been used to extract high-purity gold and silver in mining industry. Such mining activities have used a large amount of cyanide, and the mine wastewater contained a high level of cyanide has brought about pollution of surrounding aqueous environments. This research was initiated to study $TiO_2$-catalytic UV-LED photo-oxidation to remove cyanide from the mine wastewater. UV lamp has been generally used as a light source in conventional photo-oxidation so far, but it shows numerous drawbacks. For this reason, this study focused on the evaluation of applicability of UV-LED as an alternative light source in cyanide photo-oxidation process. Three types of $TiO_2$ photo-catalyst were compared in terms of performance of photo-oxidation of cyanide, and the results show that Degussa P25 was the most efficient. In addition, four types of UV-LED were tested to compare their efficiencies of cyanide photo-oxidation, and their efficacy was increased in the order of 365 nm lamp-type > 365 nm can-type > 280 nm can-type > 420 nm lamp-type. Not only did this study demonstrate that UV-LED can be used in the photo-oxidation of cyanide as an alternative light source of UV lamp, but also confirmed that the performance of photo-oxidation was significantly influenced by the type of $TiO_2$ catalysts.

• Journal of the Korean Applied Science and Technology
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• v.7 no.1
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• pp.63-70
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• 1990

Influence of mixing ratio of blending oil (rice bran oil : RBD palm olein = 1 : 1, 1 : 4 mixture: w/w) and natural tocopherol, citric acid, and sodium polyphosphate on enhancement of oxidation stability of blending oil under the condition of tap water infulx(1 ml/min/200g oil) were compared by AOM test after heating these system at l80$^{\circ}C$. In addition, the effects of tocopherol, and synergist on oxidition stability were also tested with potato chips fried with blending oil(1 : 4 mixture). The result obtained were as followes; 1. The test of RBD palm olein addition of 50% and 80% against rice bran oil on oxidation stability showed that the higher the palm olein contents in blending oil, the higher the oxidation stability. 2. The test of oxidation stability, adding l00ppm, 200ppm and 400ppm of natural tocopherol in two different types of blending oils, A(1 : 1 mixture) and B(1 : 4 mixture), disclosed that blending oil B was more positively effective, and this trend was superior at 200ppm level particularly, Furthermore, oxidation stability was enhanced remarkably upon addition of 100ppm of natural tocopherol, and 50ppm of citric acid together with 50ppm, 100ppm and 200ppm of sodium polyphosphate in general. Especially, 200ppm of sodium polyphosphate addition induced the most synergetic effect on oxidation stability showing as much as 3 times compare to control. 3. The results of oxidation stability obtained by peroxide value on potato chips fried with blending oil (1:4 mixture} added tocopherol, citric acid and sodium polyphosphate and preserved at $60^{\circ}C$ revealed that addition of tocopherol and 50ppm of citric acid together with 200ppm of sodium polyphosphate treatment was the most synergistic coinciding with AOM test results.