• Journal of Microbiology and Biotechnology
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• v.33 no.12
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• pp.1595-1605
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• 2023

Dehydroquinate dehydratase (DHQD) catalyzes the conversion of 3-dehydroquinic acid (DHQ) into 3-dehydroshikimic acid in the mid stage of the shikimate pathway, which is essential for the biosynthesis of aromatic amino acids and folates. Here, we report two the crystal structures of type II DHQD (CgDHQD) derived from Corynebacterium glutamicum, which is a widely used industrial platform organism. We determined the structures for CgDHQD^WT with the citrate at a resolution of 1.80Å and CgDHQD^R19A with DHQ complexed forms at a resolution of 2.00 Å, respectively. The enzyme forms a homododecamer consisting of four trimers with three interfacial active sites. We identified the DHQ-binding site of CgDHQD and observed an unusual binding mode of citrate inhibitor in the site with a half-opened lid loop. A structural comparison of CgDHQD with a homolog derived from Streptomyces coelicolor revealed differences in the terminal regions, lid loop, and active site. Particularly, CgDHQD, including some Corynebacterium species, possesses a distinctive residue P105, which is not conserved in other DHQDs at the position near the 5-hydroxyl group of DHQ. Replacements of P105 with isoleucine and valine, conserved in other DHQDs, caused an approximately 70% decrease in the activity, but replacement of S103 with threonine (CgDHQD^S103T) caused a 10% increase in the activity. Our biochemical studies revealed the importance of key residues and enzyme kinetics for wild type and CgDHQD^S103T, explaining the effect of the variation. This structural and biochemical study provides valuable information for understanding the reaction efficiency that varies due to structural differences caused by the unique sequences of CgDHQD.

• Food Science of Animal Resources
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• v.44 no.4
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• pp.873-884
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• 2024

Flunixin is a veterinary nonsteroidal anti-inflammatory agent whose residues have been investigated in their original form within tissues such as muscle and liver. However, flunixin remains in milk as a metabolite, and 5-hydroxy flunixin has been used as the primary marker for its surveillance. This study aimed to develop a quantitative method for detecting flunixin and 5-hydroxy flunixin in milk and to strengthen the monitoring system by applying to other livestock and fishery products. Two different methods were compared, and the target compounds were extracted from milk using an organic solvent, purified with C₁₈, concentrated, and reconstituted using a methanol-based solvent. Following filtering, the final sample was analyzed using liquid chromatography-tandem mass spectrometry. Method 1 is environmentally friendly due to the low use of reagents and is based on a multi-residue, multi-class analysis method approved by the Ministry of Food and Drug Safety. The accuracy and precision of both methods were 84.6%-115% and 0.7%-9.3%, respectively. Owing to the low matrix effect in milk and its convenience, Method 1 was evaluated for other matrices (beef, chicken, egg, flatfish, and shrimp) and its recovery and coefficient of variation are sufficient according to the Codex criteria (CAC/GL 71-2009). The limits of detection and quantification were 2-8 and 5-27 ㎍/kg for flunixin and 2-10 and 6-33 ㎍/kg for 5-hydroxy flunixin, respectively. This study can be used as a monitoring method for a positive list system that regulates veterinary drug residues for all livestock and fisheries products.

• Korean Journal of Microbiology
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• v.49 no.4
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• pp.313-320
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• 2013

Biofilm formed on stainless and copper in water treatment plant was investigated for sixteen weeks. Biofilm reactor was specially designed for this study. It was similar to that of a real distribution pipe. Raw water, coagulated, settled, filtered and treated water were used in this study. The average number of heterotrophic bacteria counts was $1.6{\times}10^4CFU/ml$, $5.8{\times}10^3CFU/ml$, $1.8{\times}10^3CFU/ml$, $1.3{\times}10^2CFU/ml$, 1 CFU/ml, respectively. Density of biofilm bacteria formed on stainless and copper pipes in raw, coagulated and settled water increased above $2.9{\times}10^3CFU/cm^2$ within second weeks while more biofilm bacteria counts were found on the stainless pipe than on the copper pipe. In case of filtered water (free residue chlorine 0.44 mg/L), there was no significant difference in the number of biofilm bacteria on both pipes and biofilm bacteria below $18CFU/cm^2$ were detected on both pipe materials after fifth weeks. Biofilm bacteria were not detected on both pipe materials in treated water (free residue chlorine 0.88 mg/L). According to the results of DGGE analysis, Sphingomonadacae was a dominant species of biofilm bacteria formed on the stainless pipe while the copper pipe had Bradyrhizobiaceae and Sphingomonadaceae as dominant bands. In case of filtered water, a few bands (similar to Propionibacterium sp., Sphingomonas sp., Escherichia sp., and etc.) that have 16S rRNA sequences were detected in biofilm bacteria formed on both pipes after fifth weeks. Stainless pipe had higher species richness and diversity than the copper pipe.

• Journal of the Korean Society of Food Science and Nutrition
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• v.34 no.2
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• pp.139-147
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• 2005

The efficacy of extraction from Inonotus obliquus was examined from the points of antioxidative characteristics and some antioxidative compounds. To enhance the efficient extraction for the effective components from Inonotus obliquus, temperature-stepwise water extraction method was applied. Temperature-stepwise water extracts were prepared for 8 hrs as follows: the first extract at 8$0^{\circ}C$, the second extract from the residue of the first extract at 10$0^{\circ}C$, and the third extract from the residue of the second extract at 12$0^{\circ}C$. Antioxidativeactivities were determined by electron-donating ability of DPPR - free radical, scavenging ability of ABTS$.$$^{+}$radical cation, and by inhibiting ability of linoleic acid autoxidation. In results, the first extract showed the least antioxidant capacity, and the third extract showed the highest antioxidant capacity. The third extract also had the greatest amounts of phenolic compounds and flavonoids. Amounts of phenolic compound from each extract were almost proportional to the radical scavenging activities and linoleic acid autoxidation inhibiting ability (r=0.960∼0.980, regression analysis). Furthermore, the effect of the pooled extract of all three extractions of Inonotus obliquus on the lipid peroxidation reacted with active oxygen species (KO$_2$, $H_2O$$_2$, $.$OH) and metals (Fe$^{2+}$, CU$^{2+}$) was evaluated by measuring the formation of thiobarbituric acid reactive substances (TBARS). The pooled Inonotus obliquus extracts lowered the amounts of TBARS formed by all of the active oxygen species and metals. Especially, these lowering effects were pronounced in the reaction with $.$OH and Fe$^{2+}$. These results suggest that the pooled temperature-stepwise extract from Inonotus obliquus could be potential functional materials to reduce the oxidation of lipids and other compounds induced by free radicals.adicals.

• Journal of Food Hygiene and Safety
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• v.34 no.3
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• pp.283-289
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• 2019

This study was performed to monitor the residual pesticides in agricultural products used in school foodservice in the Gwangju metropolitan area. Risk assessment was also carried out based on the amount of agricultural products consumed. A total of 320 agricultural products supplied to schools in Gwangju were analyzed from 2015 to 2017. The pre-treatment and residual pesticide analysis of these products was conducted in accordance with the second method for multi-residue analysis of pesticides in the Korean food code. The hazard index was calculated by dividing the estimated daily intake (EDI) of pesticides by the acceptable daily intake (ADI). The linearity correlation coefficient for the calibration curve was 0.9923 to 1.0000, LOD 0.004 to 0.019 mg/kg, LOQ 0.012 to 0.057 mg/kg, and recovery was 79.1 to 100.2%. Residual pesticides were detected in 18 (5.6%) of 320 agricultural products used for school foodservice, and one sample of sweet potato stem (0.3%) exceeded the maximum residual limit (MRL). The detection frequency for chili peppers and bell peppers was higher than that for other agricultural products. The frequently-detected pesticides were boscalid and acetamiprid. These results showed that residual pesticide management is needed for chili pepper, bell pepper and sweet potato stem among agricultural products supplied to schools. The hazard index of bifenthrin in sweet potato stem showed the highest (64.18%), and the other pesticides were 0.03-8.23%. These results indicated that agricultural products supplied to schools in Gwangju were safe for consumption. To minimize the intake of residual pesticides, it is necessary to not only thoroughly wash agricultural products but to also ensure the expanded supply of products that are pesticide-free.

• Korean Journal of Food Science and Technology
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• v.45 no.4
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• pp.391-402
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• 2013

Pesticide residues in agricultural products in Korea were evaluated to create a data base to inform food policy. Pesticide residues were investigated in 17 commodities collected from 9 provinces in 2012. Our analytical method of multiresidue analysis, involved the analysis of individual recovery, linearity, limit of detection, and limit of quantitation of 60 pesticides in six matrices. The pesticides, including acetamiprid and forchlorofenuron, were evaluated in 358 agricultural samples by liquid chromatography/tandem mass spectrometry. Twenty three pesticides were detected from 67 samples. The results showed that the ratio of estimated daily intake to acceptable daily intake was 0.00009-0.0861% by the intake assessment, which means that residual pesticides in agricultural products in Korea are properly controlled.

• Journal of Food Hygiene and Safety
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• v.28 no.1
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• pp.19-23
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• 2013

A simple and rapid method has been developed and validated for simultaneous determination of each macrolides residues (spiramycin, josamycin, tilmicosin, tylosin) in chicken muscle by high-performance liquid chromatography- photo diode array (HPLC-PDA). Chicken muscle sample have been extracted with liquid-liquid extraction process; analytes was extracted by acetonitrile, and then defatted with hexane saturated by acetonitrile. The HPLC separation was performed on a Unison UK-$C_{18}$ ($150mm{\times}3.0mm$, $3{\mu}m$) with a gradient system of 0.1% trifloroacetic acid (TFA) and 0.1% trifloroacetic acid (TFA) in acetonitrile as the mobile phase. The drugs were detected at 232 nm for spiramycin and josamycin, and 287 nm for tilmicosin and tylosin. The limits of quantification (LOQs) were between 27 and $59{\mu}g/kg$; and the intra- and inter-day precision (relative standard deviation; RSD) was between 0.9-13.2 and 2.4-13.1%, respectively in chicken muscle sample. The method may has been successfully applied for multiresidue determination of four macrolides below the maximum residue limits (MRLs) established by the European Union (EU).

• Journal of the Korean Wood Science and Technology
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• v.44 no.1
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• pp.96-105
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• 2016

This study investigated thermal properties and activation energy ($E_a$) of torrefied oak wood powders treated with various torrefaction times (0, 5, 7.5, 10 min) by using non-isothermal thermogravimetric analysis at heating rates of 10, 20, $40^{\circ}C/min$ to check the feasibility of rapidly torrefied oak wood powders as a fuel. As the torrefaction time increases, onset of thermal decomposition temperature, lignin content, and the amount of final residue of torrefied oak wood powders were accordingly increased with reduced hemicellulose content. $E_a$ was determined by using Friedman and Kissinger models and respective R-square values were over 0.9 meaning very good availability of calculated $E_a$ values. The $E_a$ values of the samples were decreased with the increase of torrefaction time and the lowest $E_a$ value ob served in the torrefied oak wood powders treated for 7.5 min showed high feasibility of rapidly torrefied oak wood powder as a biomass-solid refuse fuel.

• Proceedings of the Korea Society of Poultry Science Conference
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• 2005.11a
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• pp.44-52
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• 2005

The study, using sequence analysis and phylogenetic relationship of the fusion protein gene, divided the Korean epizootic isolates of Newcastle disease virus (NDV) into several lineages to determine the molecular epidemiology of the virus. A 695 base pair fragment was amplified by polymerase chain reaction between matrix protein gene and fusion protein gene of 30 Korean NDV isolates, which were isolated from field outbreaks of Newcastle disease between 1949 and 2002. All isolates showed the amino acid sequence 112 R-R-Q/R-K-R116 at the C-terminus of the F2 protein and phenylalanine (F) at the N-terminus of the F1 protein, residue 117. These amino acid sequences were identical to a known virulent motif. The region of the F gene between nucleotides 47 and 435 was compared by phylogenetic analysis. Based on nucleotide sequence, the Korean NDV isolates belonged to genotype III, V, VI and VII corresponding to isolates in 1949, 1982 to 1984, 1988 to 1997, and 1995 to 2002, respectively. These data showed that genotypes of five Korean Newcastle disease epizootics had replaced each other serially (III, V, VI and VII) in chronological order. Further, the five Korean Newcastle disease epizootics were closely related with the Necastle disease panzootics or Newcastle disease epizootics in other countries. Present study showed that the Korean genotype V isolated before 1984 was related with European Newcastle disease epizootics in the 1970s, whereas the Korean genotype VI and VII isolated after 1988 were more closely related with Far East Newcastle disease epizootics, especially Newcastle disease3 epizootics in Japan, Taiwan and China. Since 1988, the genotype VI and VII of Far East origin were dominant in South Korea. That might be due to the increased trade of agricultural products including poultry among Far East Asian countries.

• Korean Journal of Veterinary Research
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• v.46 no.4
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• pp.295-304
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• 2006

Residual materials such as veterinary drugs, environmental contaminants, and pesticides are affecting food safety. High resolution techniques and quality controls are needed to analyze these materials from part per million to part per trillion quantities in food. In order to achieve quality results, standardized methods and techniques are required. Our laboratories were prepared to obtain a certificate of accreditation for ISO/IEC 17025 in the analytical criteria of animal drugs, dioxins, pesticides, and heavy metals. ISO together with IEC has built a strategic partnership with the World Trade Organization with the common goal of promoting a free and fair global trading system. ISO collaborates with the United Nations Organization and its specialized agencies and commissions, particularly those involved in the harmonization of regulations and public policies including the World Health Organization and CODEX Alimentarius for food safety measurement, management and traceability. Our goal was to have high quality analysts, proper analytical methods, good laboratory facilities, and safety systems within guidelines of ISO/IEC 17025. All staff members took requirement exams. We applied proficiency tests in the analysis of veterinary drugs (nitrofuran metabolites, sulfonamide and tetracyclines), dioxins, organophosphorus pesticides, and heavy metals (Cd, Pb, As) to the Food Analysis Performance Assessment Scheme (FAPAS) at Central Science Laboratory, Department for Environment Food and Rural Affairs (DEFRA), England. The results were very satisfactory. All documents were prepared, including system management, laboratory management, standard operational procedures for testing, reporting, and more. The criteria encompassed the requirements of ISO/IEC 17025:1999. Finally, the Korea Laboratory Accreditation Scheme (KOLAS) accredited our testing laboratories in accordance with the provisions of Article 23 of the National Standards Act. The accreditation will give us the benefit of becoming a regional reference laboratory in Asia.