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Biomedical subjects

D Ryu

Publications and source records attributed to D Ryu.

9 recordsLinked to original sources
PubMed2001

Natural occurrence of aflatoxins in Korean meju.

Aflatoxin B1 (AFB1) was found in 35 of 60 (58.3%) meju samples with an average concentration of 7.3 ng/g by ELISA. Contamination of AFB1 was confirmed in 25 of 60 samples (41.6%) using HPLC, with an average concentration of 6.9 ng/g. Mean recoveries from meju ranged from 107% to 170% for AFB1 using ELISA at a spiking range of 1 to 50 ng/g. Over the same range, recoveries using HPLC were from 70% to 83%. The levels of AFB1 determined by ELISA and by HPLC demonstrated a close relationship between the two methods (r2 = 0.9324) employed in this study. In order to evaluate the potential health risks of AFB1 on Koreans consuming meju, we calculated the estimated probable daily intake (PDI) based on the average contamination levels and compared it with the estimated tolerable daily intake (TDI). The PDIs of AFB1 from kanjang and dwenjang were determined to be 0.04 and 0.21 ng/kg bw/day, respectively, and were higher than TDIs.

Aflatoxin B1↗
PubMed2000

Occurrence of aflatoxin M1 in Korean dairy products determined by ELISA and HPLC.

The occurrence of aflatoxin M1 (AFM1) in pasteurized milk and dairy products was investigated by using direct competitive enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (HPLC). The recoveries of AFM1 from the samples spiked at levels between 5 and 500 pg/ml were 88.0-106.5% for pasteurized milk and 84.0-94.0% for yoghurt by ELISA. By HPLC, the recoveries were 103-120% for pasteurized milk and 87.0-93.0% for yoghurt. The limits of detection were found to be 2 pg/ml by ELISA and 10 pg/ml by HPLC. Among a total of 180 samples collected in Seoul, Korea, the incidence of AFM1 in pasteurized milk, infant formula, powdered milk and yoghurt was 76, 85, 75, and 83%, respectively, with a mean concentration of 18, 46, 200, and 29 pg/g, respectively, when determined by ELISA. These results obtained by ELISA were closely related to those by HPLC for AFM1 (r2 = 0.9783).

Aflatoxin M1↗
PubMed1999

Enhanced Cloud Disruption by Magnetic Field Interaction.

We present results from the first three-dimensional numerical simulations of moderately supersonic cloud motion through a tenuous, magnetized medium. We show that the interaction of the cloud with a magnetic field perpendicular to its motion has a great dynamical impact on the development of instabilities at the cloud surface. Even for initially spherical clouds, magnetic field lines become trapped in surface deformations and undergo stretching. The consequent field amplification that occurs there and, in particular, its variation across the cloud face then dramatically enhance the growth rate of Rayleigh-Taylor unstable modes, hastening the cloud disruption.

Journal Article↗
PubMed1999

Effect of cycling temperatures on the production of deoxynivalenol and zearalenone by Fusarium graminearum NRRL 5883.

The effects of three regimens of cycling incubation temperatures and incubation at constant 25 degrees C on the growth of Fusarium graminearum NRRL 5883 and production of deoxynivalenol (DON) and zearalenone (ZEN) on rice were compared. The effects of low-temperature stress were also studied by incubating rice cultures at a constant 15 degrees C for 4 weeks following incubation at constant 25 degrees C for 2 weeks. Both incubation temperature and time significantly (P < or = 0.05) affected growth of F. graminearum NRRL 5883 and production of DON and ZEN. The highest amount of free ergosterol (640 microg/g culture material) that was used as a measure of fungal growth was found in cultures incubated at temperatures cycling between 15 and 30 degrees C during a 6-week period. The highest amounts of DON (1,679 microg/g culture material) and ZEN (603 microg/g culture material) were produced in cultures incubated at a constant 25 degrees C for 2 weeks prior to incubation at a constant 15 degrees C for an additional 4 weeks. Under cycling incubation temperatures, maximum amounts of DON (850 microg/g culture material) and ZEN (98 microg/g culture material) were produced in cultures incubated at temperatures cycling between 15 and 30 degrees C for 6 weeks. Overall, there was no correlation between mold growth and production of either DON or ZEN. However, DON production and ZEN production were correlated.

Chromatography, High Pressure Liquid↗
PubMed1999

Fumonisin B1 production by Fusarium moniliforme and Fusarium proliferatum as affected by cycling temperatures.

The effects of temperatures cycling between 5 and 20 degrees C, 10 and 25 degrees C, and 15 and 30 degrees C on the production of fumonisin B1 (FB1) and ergosterol by Fusarium moniliforme and Fusarium proliferatum on rice was studied. Temperatures were cycled at 12-h intervals by manually moving cultures from one temperature to another. Constant temperature incubation at 25 degrees C and a low temperature stress were compared with the cycling temperature incubations. Low temperature stress was achieved by incubating rice cultures at 25 degrees C for 2 weeks followed by 15 degrees C for 4 weeks. The maximum yields of FB1 were found to be 247 microg/g by F. moniliforme at temperatures that cycled between 10 and 25 degrees C after 2 weeks and 284 microg/g by F. proliferatum when the temperatures cycled between 5 and 20 degrees C after 6 weeks. Ergosterol content of the rice cultures was also monitored. Overall, the two Fusarium species showed differences in production of FB1 and ergosterol under the various temperature treatments. The most notable differences were that the temperature treatments that stimulated greatest FB1 production were different for each species: cycling temperatures between 10 and 25 degrees C for F. moniliforme and cycling temperatures between 5 and 25 degrees C for F. proliferatum. At most temperatures, F. proliferatum produced more ergosterol than F. moniliforme. Maximum production of ergosterol by F. proliferatum occurred at 6 weeks, with temperatures that cycled between 10 and 25 degrees C, whereas F. moniliforme produced maximum amounts of ergosterol at 6 weeks, with temperatures that cycled between 15 and 30 degrees C.

Carboxylic Acids↗
PubMed1999

Stability of zearalenone during extrusion of corn grits.

The effects of extrusion cooking on the stability of zearalenone (ZEN) in spiked (4.4 microg/g) food-grade corn grits were investigated using a twin screw extruder. A ground rice culture material containing a high level of ZEN was used to spike the corn grits. The extrusion variables were screw type (mixing and nonmixing), temperature (120, 140, and 160 degrees C), and moisture content (18, 22, and 26%). Both unextruded and extruded samples were analyzed for ZEN by high-performance liquid chromatography. Extrusion cooking of the corn grits resulted in significant reductions of ZEN in grits extruded with either mixing screws or nonmixing screws, but use of mixing screws was somewhat more effective (66 to 83%) overall than nonmixing screws (65 to 77%). Greater reduction of ZEN was observed at either 120 or 140 degrees C than at 160 degrees C. The moisture content of corn grits was not a significant factor affecting reduction of ZEN during extrusion with either mixing or nonmixing screws.

Chromatography, High Pressure Liquid↗
PubMed1985

Construction of killer wine yeast strain.

A double-stranded RNA plasmid which confers the superkiller phenotype was transferred into a wine yeast (Montrachet strain 522) and its leucine-requiring derivative (strain 694) by cytoduction, using the protoplast fusion technique. The killer wine yeast constructed completely suppressed the growth of killer-sensitive strains of Saccharomyces cerevisiae in yeast extract-peptone-glucose medium at pH 4.5, whereas the killer effect was somewhat decreased at pH 3.5. The wine yeast harboring the killer factor also inhibited the growth of killer-sensitive cells satisfactorily when it was grown in grape juice.

Journal Article↗