Jueun Kim

Mycotoxin production of Alternaria strains isolated from Korean barley grains determined by LC-MS/MS

Twenty-four Alternaria strains were isolated from barley grain samples. These strains were screened for the production of mycotoxins on rice medium using thin layer chromatography. All 24 strains produced at least one of the five mycotoxins (ALT, AOH, ATX-I, AME, and TeA). Three representative strains, namely EML-BLDF1-4, EML-BLDF1-14, and EML-BLDF1-18, were further analyzed using a new LC-MS/MS-based mycotoxin quantification method. This method was used to detect and quantify Alternaria mycotoxins. We used positive ion electrospray mass spectrometry with multiple reaction mode (MRM) for the simultaneous quantification of various Alternaria mycotoxins produced by these strains. Five Alternaria toxins (ALT, ATX-I, AOH, AME, and TeA) were detected and quantified. Sample preparation included methanol extraction, concentration, and injection into LC-MS/MS. Limit of detection ranged from 0.13 to 4μg/mL and limit of quantification ranged from 0.25 to 8μg/mL.

Characterization of Nivalenol-Producing Fusarium culmorum Isolates Obtained from the Air at a Rice Paddy Field in Korea

Together with the Fusarium graminearum species complex, F. culmorum is a major member of the causal agents of Fusarium head blight on cereals such as wheat, barley and corn. It causes significant yield and quality losses and results in the contamination of grain with mycotoxins that are harmful to humans and animals. In Korea, F. culmorum is listed as a quarantine fungal species since it has yet to be found in the country. In this paper, we report that two isolates (J1 and J2) of F. culmorum were collected from the air at a rice paddy field in Korea. Species identification was confirmed by phylogenetic analysis using multi-locus sequence data derived from five genes encoding translation elongation factor, histone H3, phosphate permease, a reductase, and an ammonia ligase and by morphological comparison with reference strains. Both diagnostic PCR and chemical analysis confirmed that these F. culmorum isolates had the capacity to produce nivalenol, the trichothecene mycotoxin, in rice substrate. In addition, both isolates were pathogenic on wheat heads and corn stalks. This is the first report on the occurrence of F. culmorum in Korea.

Development and validation of a modified QuEChERS method coupled with LC-MS/MS to determine arbutin in pear peels

A new effective method was developed to determine the concentration of arbutin in pear peels using a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The original QuEChERS was modified to enable the extraction of the polar arbutin molecule. Use of an initial 50:50 acetonitrile:water extraction solvent led to the highest extraction efficiency. The arbutin extracted from pear peels was found to be identical to the β-arbutin standard, as confirmed by NMR and LC-MS/MS analyses. For quantitative analysis, the mass spectra of the precursor ion [M+NH4]+ at m/z 290.0 and the product ion of arbutin at m/z 163.0 were used. The limit of detection, limit of quantification, linearity, precision, accuracy, and recovery of the proposed method were evaluated. We successfully applied this method to pear samples and it may be suitable for the quantitative analysis of arbutin in other similar plant materials.

Power Electronics Converter Education Program using LabVIEW

This paper deals with power electronic converter education program using LabVIEW. LabVIEW is a graphic based programming language with easy debugging, which is suitable for education program that can be used to study and figure out the operation of power electronic converters. When LabVIEW is employed as a simulation program of the operation of power electronic converters, the resulting program has the advantage such that the effects of the change of control variables and circuit parameters on the various variables such as the output voltage and the inductor current etc can be directly displayed without any separate compiling procedure. This paper shows the design procedure and the characteristics of the power electronics education program implemented by LabVIEW focusing on DC-DC converter among power electronic converters.

Isolation and structural elucidation of pelgipeptin E, a novel pore-forming pelgipeptin analog from Paenibacillus elgii with low hemolytic activity

Pelgipeptins are cyclic lipopeptides composed of nine amino acids and a short fatty acid chain. In the present study, we report a novel pelgipeptin peptide that was isolated from Paenibacillus elgii BC34-6 and named pelgipeptin E (PGP-E). The molecular mass of PGP-E was 1072 Da as determined by liquid chromatography-mass spectrometry and the amino acid sequence was elucidated by tandem mass spectrometry. The complete molecular structure of PGP-E was characterized using 2D NMR spectroscopy. PGP-E consisted of a cyclic peptide backbone of Dab1-Val2-Dab3-Phe4-Leu5-Dab6-Val7-Leu8-Ser9 and a lipid chain (-CH2CH2CH3). PGP-E had broad antimicrobial activity against gram-negative and -positive bacteria, including methicillin-resistant Staphylococcus aureus strains. Furthermore, the mode of action of PGP-E was investigated using calcein dye leakage and membrane depolarization assays, which suggest that PGP-E acts via a membrane-active mechanism. The hemolytic activity of PGP-E was significantly lower than that of melittin, a well-known membrane-active peptide derived from bee venom. These results suggest that PGP-E is a potential candidate in the development of new peptide antibiotics.