Sangsuk Oh

Molecular epidemiology of norovirus infections in children with acute gastroenteritis in South Korea in November 2005 through November 2006.

ABSTRACT Norovirus infections were detected in 114 of 762 children with acute gastroenteritis in South Korea from November 2005 to November 2006. Seasonality peaks in December, March, and October were also assessed in this study. We identified seven noroviral genotypes (GI-6, GII-2, GII-3, GII-4, GII-5, GII-6, and GII-8) and a C1-120 strain showing low identity (79.3%) with GII-13 and GII-17.

Inactivation of Bacillus cereus spores by high hydrostatic pressure at different temperatures

The effect of pH on the initiation of germination and on the inactivation of Bacillus cereus (KCTC 1012) spores during high hydrostatic pressure processing (HPP) with pressures of 0.1 to 600 MPa at different temperatures was investigated. Two different high-pressure treatments were adopted to evaluate the effect of pH on the inactivation of B. cereus on sporulation medium and in suspension medium. Inactivation of B. cereus spores with HPP treatment was affected more by sporulation medium pH than by suspension medium pH. B. cereus spores obtained through sporulation at pH 6.0 showed more resistance to inactivation by HPP at 20, 40, and 60 degrees C than did those obtained through sporulation at pHs of 7.0 and 8.0. Constituents of B. cereus spores obtained through sporulation at pH 6.0 may undergo electrochemical charge changes comparable to those for spores obtained through sporulation at pH 7.0. The initiation of B. cereus spore germination was more sensitive to pressure around 300 MPa at 20 degrees C. Increasing processing temperatures during HPP enhanced the effect of sporulation medium pH (i.e., environmental pH) on the inactivation of B. cereus spores.

Aroma dilution method using GC injector split ratio for volatile compounds extracted by headspace solid phase microextraction

Abstract Dilution methods are widely used for the screening of aroma-active compounds in gas chromatography-olfactometry (GC-O). An aroma dilution method for the samples extracted by headspace solid phase microextraction (HS–SPME) was developed using GC injector split ratio. In an aqueous model system containing seven authentic standards, the relationship between logarithmic peak area and logarithmic split ratio showed a high linearity as indicated by the good agreement between calculated and experimental data. This result suggests that the split ratio is a suitable and reliable tool for the successive dilution of volatiles in HS-SPME–GC-O. When this method was applied to yuzu ( Citrus junos ) tea, linalool (floral/lemon) and decanal (orange/waxy) were identified as the most intense aroma-active compounds.

Prevalence and toxigenic profiles of Bacillus cereus isolated from dried red peppers, rice, and sunsik in Korea.

Bacillus cereus is a spore-forming foodborne pathogen responsible for diarrheal and emetic types of food poisoning. Intoxication is caused by various enterotoxins or by emetic toxin. Because of its widespread presence and the ability to form heat-stable endospores in a relatively short time, B. cereus has been difficult to control. In this study, 21 rice and 36 Sunsik (a mixture of powdered raw grains) samples were examined for the prevalence of B. cereus. A multiplex PCR assay was used to evaluate the distribution of 10 different toxigenicity-related genes among 1,082 B. cereus strains isolated from dried red peppers (919 isolates), rice (98 isolates), and Sunsik (65 isolates). The results suggest that (i) the examined foods were free of the emetic toxin but not free of enterotoxins and (ii) the distribution of enterotoxigenic genes was significantly different among the B. cereus isolates from various sources.

Simultaneous identification of seven foodborne pathogens and Escherichia coli (pathogenic and nonpathogenic) using capillary electrophoresis-based single-strand conformation polymorphism coupled with multiplex PCR.

The objective of this study was to develop a novel technique for parallel analysis of eight important foodborne microbes using capillary electrophoresis-based single-strand conformation polymorphism (CE-SSCP) coupled with multiplex PCR. Specific primers for multiplex PCR amplification of the 16S rRNA gene were designed, corresponding to eight species of bacteria, including Escherichia coli, Clostridium perfringens, Campylobacter jejuni, Salmonella enterica, Listeria monocytogenes, Vibrio parahaemolyticus, Staphylococcus aureus, and Bacillus cereus, for the species-specific identification and optimal separation of their PCR products in subsequent analysis by CE-SSCP. Multiplex PCR conditions including annealing temperature, extension time, the number of PCR cycles, and primer concentrations were then optimized for simultaneous detection of all target foodborne bacteria. The diagnostic system using CE-SSCP combined with multiplex PCR developed here can be used for rapid investigation of causative agents of foodborne illness. The simplicity and high sensitivity of the method may lead to improved management of safety and illness related to food.

Effects of enzymatic hydrolysis of buckwheat protein on antigenicity and allergenicity.

BACKGROUND/OBJECTIVES Due to its beneficial health effects, use of buckwheat has shown a continuous increase, and concerns regarding the allergic property of buckwheat have also increased. This study was conducted for evaluation of the hydrolytic effects of seven commercial proteases on buckwheat allergens and its allergenicity. MATERIALS/METHODS Extracted buckwheat protein was hydrolyzed by seven proteolytic enzymes at individual optimum temperature and pH for four hours. Analysis was then performed using SDS-PAGE, immunoblotting, and competitive inhibition ELISA (ciELISA) with rabbit antiserum to buckwheat protein, and direct ELISA with pooled serum of 21 buckwheat-sensitive patients. RESULTS Alkaline protease, classified as serine peptidase, was most effective in reducing allergenicity of buckwheat protein. It caused decomposition of the whole buckwheat protein, as shown on SDS-PAGE, and results of immunoblotting showed that the rabbit antiserum to buckwheat protein no longer recognized it as an antigen. Allergenicity showed a decrease of more than 50% when pooled serum of patients was used in ELISA. Two proteolytic enzymes from Aspergillus sp. could not hydrolyze buckwheat allergens effectively, and the allergenicity even appeared to increase. CONCLUSIONS Serine-type peptidases appeared to show a relatively effective reduction of buckwheat allergenicity. However, the antigenicity measured using rabbit antiserum did not correspond to the allergenicity measured using sera from human patients. Production of less allergenic buckwheat protein may be possible using enzymatic hydrolysis.

Characterization and stability analysis of zinc oxide nanoencapsulated conjugated linoleic acid.

Nanoencapsulation technology has a diverse range of applications, including drug-delivery systems (DDS) and cosmetic and chemical carriers, because it can deliver various bio- and organic-molecules and improve their stabilities. Conjugated linoleic acid (CLA) has health benefits, including being an anticancer agent, but it decreases flavor due to volatiles from oxidation. To improve the stability of CLA for food applications, nanoencapsulated CLA was synthesized for use in zinc basic salt (ZBS) and characterized by powder X-ray diffractometry, thermogravimetric analysis (TGA), elemental CHN analysis, inductively coupled plasma (ICP) analysis, UV/VIS spectroscopy, and FTIR spectroscopy. The thermal stability of nanoencapsulated CLA at 180 degrees C, a temperature similar to that used in cooking, was analyzed by gas chromatography. The gallery height of nanoencapsulated CLA was determined to be approximately 26 A through powder X-ray diffractometry; therefore, the CLA molecules were closely packed with zig-zag form between the intracrystalline spaces of nano particles. Elemental CHN analysis and ICP data determined the chemical composition of nanoencapsulated CLA to be Zn(4.86)(OH)(8.78)(CLA)(0.94). By TGA, it was determined about 45% (wt/wt) of weight loss corresponded to CLA, which is good agreement with the 42.13% (wt/wt) determined from high-performance liquid chromatography (HPLC) and elemental CHN analysis. UV/VIS spectroscopy and Fourier-transformed infrared (FTIR) spectroscopy showed encapsulated CLA maintained a conjugated diene structure, supporting the presence of CLA. Nanoencapsulation improved the thermal stability of CLA by about 25%, compared to pristine CLA. Practical Application: This system can be used for protection of encapsulated negatively-charged food ingredients from thermal processing.

Molecular Characterization of Two Strains of Porcine Group C Rotavirus

Group C rotaviruses are an important cause of acute gastroenteritis in humans and animals. Fecal samples were collected from a porcine herd in July, 2009. Group C rotavirus RNA was detected using RT-PCR for the VP6 gene. The identified strain was further characterized by sequencing and phylogenetic analysis of the partial VP4, and complete VP6 and VP7 gene sequences. The partial VP4 and complete VP6 gene sequences of the CUK-5 strain were most closely related to those of the CUK-6 strain of group C rotaviruses. Phylogenetic analysis of the VP7 gene of the 2 strains (CUK-5 and CUK-6) and reference strains of group G rotavirus by the neighbor-joining method also confirmed that CUK-5 and CUK-6 belonged to type G5 and G1 strains, respectively. This study provides useful data for the prediction of newly appearing variants of porcine group C rotaviruses in neighboring countries through comparisons with GCRVs and fundamental research for vaccine development.

A sensitive enzyme immunoassay for amygdalin in food extracts using a recombinant antibody.

Amygdalin (laterile) is a cyanogenic glycoside commonly found in the pits of many fruits and raw nuts. When amygdalin-containing seeds are crushed and moistened, free cyanide is formed. Pits and nuts containing unusually high levels of amygdalin can therefore cause cyanide poisoning, and detection of amygdalin in food extracts can be a life-saving measure. In this study, we generated recombinant antibodies against amygdalin from a phage display of a combinatorial rabbit/human chimeric antibody library and used it in a sensitive competition enzyme immunoassay system to detect amygdalin in extracts of pits and nuts. The detection limit was determined to be 1 x 10(-9) M.

Profiling and Priority Selection of Foodborne Pathogens in Fresh Produce

There have been growing concerns among people about food safety due to insufficient information on foodborne pathogens. In this study, we developed a risk priority of 15 foodborne pathogens. For the priority deter- mination we collected risk profile criteria information from CODEX Alimentarius Commission and developed coun- tries. The basis for criteria we selected from information of surveillance were frequency and severity of disease, frequency of consumption and probability of cross-contamination. We also considered foodborne pathogens which have been managed in developed countries though those pathogens are not currently managed appropriately in Korea. Priorities were divided into three groups following these consideration. The first priority group includes Norovirus, pathogenic E. coli, Salmonella spp, Clostridium botulinum and Listeria monocytogenes. The second priority group includes Vibrio parahaemolyticus, Stapylococcus aureus, Campylobacter jejuni and Bacillus cereus, and the third pri- ority group includes Clostridium perfringens, Yersinia enterocolitica, Shigella spp, Cronobacter sakazakii and Hepa- titis A virus. Our results could be applied to prevent foodborne illness from fresh produce.