• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.9
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• pp.1561-1565
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• 2007

According to thermal degradation on power transformers, it is known that electrical, mechanical and chemical characteristics for power transformer's oil-paper are changed. In the chemical property, especially, when the kraft paper is aged, the cellulose polymer chains break down into shorter lengths. It causes decrease in both tensile strength and degree of polymerization of paper insulation. Also the paper breakdown is accompanied by an increase in the content of various furanic compounds within the dielectric liquid. It is known that furanic components in transformer oil come only from the decomposition of insulating paper rather than from the oil itself. Therefore the analysis of furanic degradation products provides a complementary technique to dissolved gas analysis for monitoring transformers when we evaluate the aging of insulating paper by the total concentration of carbon monoxide and carbon dioxide dissolved in oil only. Recently, the analysis of furanic compounds by high performance liquid chromatography(HPLC) using IEC 61198 method for estimating degradation of paper insulation in power transformers has been used more conveniently for assessment of oil-paper. It is know that the main products which is produced by aging are 2-furfuryl alcohol, 2-furaldehyde(furfural), 2-furoic acid, 2-acetylfuran, 5-methyl-2-furaldehyde, and 5-hydroxymethyl-2-furaldehyde. For investigating the accelerated aging process of oil-paper samples we manufactured accelerating aging equipment and we estimated variation of insulations at $140^{\circ}C$ temp. during 500 hours. Typical transformer proportions of copper, silicon steel and iron have been added to oil-paper insulation during the aging process. The oil-paper insulation samples have been measured at intervals of 100 hours. Finally we have analyzed that 2-furoic acid and 2-acetylfuran products of furanic compounds were detected by HPLC, and their concentrations were increased with accelerated aging time.

• Korean Journal of Agricultural Science
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• v.48 no.4
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• pp.899-910
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• 2021

This study was performed to suggest concentration methods leading to the production ofhoney with an excellent flavor by examining the effects of the concentration temperature and method on changes in 5-hydroxymethyl-2-furaldehyde (5-HMF) levels and the flavor components of honey. The 5-HMF contents of honey samples concentrated in a tray concentrator at 45, 50, 60, and 70℃ were 2.1, 2.3, 2.5, and 3.1 mg·kg^-1, respectively, demonstrating that the 5-HMF contents increased as the concentration temperatures were increased. The honey vacuum-concentrated at 70℃ showed a higher 5-HMF content than that at 60℃, similar to the tray-concentrated honey at different temperatures. The main and other minor flavor components of the honey were volatilized and significantly reduced after vacuum concentration. In the tray concentration, all of the honey samples concentrated at 40, 50, 60, and 70℃ showed flavor component patterns similar to each other, and most of the main and other minor flavor components in the honey were volatilized and significantly reduced after tray concentration. As such, most of the main and other minor flavor components of the honey were mostly removed at 70℃ after both the vacuum concentration and tray concentration processes. The effects of the concentration method and temperature on the viscosity, 5-HMF level, and flavor components of the honey were found to be significant in this study. Given that the components of honey were shown to undergo significant physicochemical changes depending on the concentration method used and temperature during laboratory-scale production, the concentration methods devised in this study can be applied industrially.

• Korean Journal of Pharmacognosy
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• v.42 no.2
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• pp.117-126
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• 2011

Twenty-two compounds were isolated from the 70% ethanolic extract of Rehmanniae Radix Preparata (Scrophulariaceae) and their structures were identified as three triterpenoids [oleanolic acid (1), pomonic acid (2) and ursolic acid (5)], an iridoid, catalpol (13), four furan derivatives [5-hydroxymethyl-2-furaldehyde acetate (3), 5-hydroxymethyl-2-furfural (6), 5-hydroxymethyl-2-furancarboxylic acid (7), and 5-(${\alpha}$-D-galactopyranosyloxymethyl)-2-furancarboxaldehyde (15)], three phenethyl alcohol glycosides [darendoside B (14), phenethyl alcohol 2-O-${\beta}$-D-xylopyranosyl(1${\rightarrow}$6)-${\beta}$-D-glucopyranoside (17), and salidroside (19)], four sugar derivatives [L-arabinose (11), raffinose (20), stachyose (21), and mannitol (22)], and seven others [2,5-dihydroxyacetophenone (4), succinic acid (8), daucosterol (9), ${\beta}$-sitosterol (10), adenosine (16), uridine (18) jio-cerebroside (12)]. The chemical structures of these compounds were identified on the basis of spectroscopic methods and comparison with literature values. This is the first report of the triterpenoids oleanolic acid (1), pomonic acid (2), and ursolic acid (5) from the genus Rehmannia, as well as the first report of compounds 5-hydroxymethyl-2-furaldehyde acetate (3), 2,5-dihydroxyacetophenone (4), daucosterol (9), darendoside B (14), 5-(${\alpha}$-D-galactopyranosyloxymethyl)-2-furancarboxaldehyde (15), adenosine (16), phenethyl alcohol 2-O-${\beta}$-D-xylopyranosyl(1${\rightarrow}$6)-${\beta}$-D-glucopyranoside (17), and salidroside (19) from the Rehmanniae Radix Preparata.

• Preventive Nutrition and Food Science
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• v.13 no.1
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• pp.54-59
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• 2008

This study was conducted to investigate the effect of pH on the formation of furfural compounds from glucose and fructose reacting with amino acid enantiomers in the Maillard reaction. Hydroxymethylfurfural (HMF) content was highest at pH 4.0, and decreased with increasing pH. HMF was significantly higher in glucose-based systems than fructose-based systems. Furfuryl alcohol (FFA) and 5-methyl-2-furaldehyde (MF) were not increased with increasing pH, and only small amounts were formed. In addition, 2-furaldehyde (F) was found to increase in the systems, as pH increased. However, the content was small and variable. 2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) was only found in Glc/D-Asn, Glc/L-Lys and Fru/D-Lys system, but the content was not increased with increasing pH. 2-acetylfuran (AF) was higher in Glc (or Fru)/L-Lys and Glc (or Fru)/D-Lys systems at pH 7.0. However, at pH 4.0, the content of AF was higher in the Glc (or Fru)/Gly and Glc (or Fru)/L-Asn systems. Therefore, this study aimed to observe the effect of pH, sugars and amino acid enantiomers on the production of furfural and related compounds by the Maillard reaction. A clear tendency was observed for some classes of compounds to be more easily formed at higher or lower pH. HMF was more readily formed at lower pH, while FFA, F, DMHF and MF were inhibited by acidic conditions. Particularly, compounds like FFA, F and MF were not affected by pH changes. In addition, DMHF and MF were only formed in L-Lys and D-Lys system.

• Korean Journal of Oriental Medicine
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• v.4 no.1 s.4
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• pp.115-127
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• 1998

To improve the quality control of frequently used oriental medicinal plants, the storage, cutting, processing and decokting methods of Rehmannia glutinosa Libosch. var. purpurea Makino(熟地黃) were examined. The contents of 5-hydroxymethyl-2- furaldehyde(5-HMF) of Rehmannia glutinosa Libosch. var. purpurea Makino were analysed by HPLC at various conditions as the standard component. Raw materials were classified into 3 groups with their specific gravity(天 地 人黃) and determined the ding weights and the contents of water, the solid component of Ji-Hwang(地黃) was the most. Rehmannia glutinosa Libosch. var purpurea Makino was steamed and dried nine times and analysed the content of 5-HMF on every time. In the case of Ji-Hwang, the standard component of the ninth sample was produced the most. But which of the tenth samples of Chun-Hwang and Yin-Hwang(天黃 人黃) were the most. The best decokting conditions which were determined by the yield of 5-HMF were as follows : non cutting, soaking time was 0 minutes, decokting time was 75 minutes after boiling. The contents of sugar on each of samples were determined. The contents of standard component increased by steaming number and the contents of sugar decreased.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2023.04a
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• pp.12-12
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• 2023

Plant biomass, or lignocellulose, is one of the most abundant natural resources on earth. Lignocellulosic biomass, such as agricultural and forestry residue, serves as a renewable feedstock for microbial cell factories due to its low price and abundant availability. However, the recalcitrance of lignocellulosic biomass requires a pretreatment process prior to microbial fermentation, from which fermentable sugars including xylose and glucose are generated along with various inhibitory compounds. The presence of furan derivatives, such as 5-hydroxymethyl-2-furaldehyde and 2-furaldehyde (furfural), hampers the microbial conversion of lignocellulosic biomass into value-added commodities. In this study, furfural tolerance was improved by investigating the detoxification mechanism in non-model yeast. The genes encoding aldehyde dehydrogenases were overexpressed to enhance furfural tolerance and resulted in improving cell growth and lipid production that can be converted into biofuel. Taken together, this approach contributes to the understanding of the reducing toxicity mechanism of furfural by the aldehyde dehydrogenases and provides a promising strategy that the use of microorganism as an industrial workhorse to treat efficiently lignocellulosic biomass as sustainable plant derivatives.

• Natural Product Sciences
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• v.18 no.3
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• pp.200-203
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• 2012

The chromatographic separation of a methanol extract of Prunus mume (Rosaceae) led to the isolation of 5-hydroxymethyl-2-furaldehyde (1), 4-O-caffeoylquinic acid methyl ester (2), prunasin (3), 5-O-caffeoylquinic acid methyl ester (4), benzyl-O-${\beta}$-D-glucopyranoside (5), and liquiritigenin-7-O-${\beta}$-D-glucopyranoside (6). Their structures were determined by 1D, 2D-NMR and MS data analysis as well as by comparison of their data with the published values.

• Korean Journal of Pharmacognosy
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• v.41 no.1
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• pp.58-61
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• 2010

Medicinal plant Rehmanniae Radix has long been used as traditional herbal medicine in Korea. In this study, we investigated quantitative changes of marker substance 5-hydroxymethyl-2-furaldehyde (5-HMF) in Rehmanniae Radix Preparata fermented with Ganoderma lucidum, Paecilomyces japonica, honey, and Nuruk, using HPLC according to the Korean Pharmacopoeia. As a result, 5-HMF was decreased in SDT and SYT, and increased in SST and SNT, comparing with control group. Quantitative increasing of 5-HMF is not exactly in direct proportion with fermentation, and it is need further studies to elucidate mechanism of quantitative changes by converted and newly produced substances with fermentation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.10
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• pp.1869-1873
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• 2010

For reliable operation of oil-filled electrical equipment, monitoring and maintenance of insulating oil is essential. Dissolved gas analysis(DGA) is widely used for monitoring faults in high voltage electrical equipment in service. Therefore, oil analysis should be monitored regularly during its service life. KEPCO has investigated thousands of dissolved gas analysis data since 1985, and conducted studies on the relationship of gas in oil analysis and internal inspection results of transformer. As the results, KEPCO revised criteria for transformer diagnosis and has applied it since 2008. Almost of 100 cases of internal inspection results since 2001 have been investigated. This paper presents the correlation of the fault-identifying gases with faults found in actual transformers and how should we approach to internal inspection of transformer by dissolved gas analysis.

• Journal of Life Science
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• v.27 no.4
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• pp.471-475
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• 2017

Freezing pretreatment can destroy the cell membrane of garlic and may improve some food-quality of garlic. Therefore we investigated the effect of freezing pretreatment at $-20^{\circ}C$ and $-70^{\circ}C$ on quality of aged black garlic, compared with traditional processing methods. Our results showed that freezing pretreatment at $-70^{\circ}C$ had the greatest impact on qualities and antioxidant activities of black garlic. Browning degree and pH of black garlic after both the freezing pretreatment and aging process were 3.14 and 3.55, respectively. Furthermore, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity and reducing power of aged black garlic can be enhanced by pre-freezing processing. Reducing sugar and 5-hydroxymethyl-2-furaldehyde (5-HMF) contents of freezing pretreated and aged black garlic were increased by 1.69 and 1.14 fold, respectively, compared with the control samples. The results indicated that freezing pretreatment had improved the overall qualities (such as browning degree, pH, reducing sugar) and functional materials of black garlic.