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Cheongju, South Korea

Feng X.,Iowa State University | Lee E.J.,University of Wisconsin - Stout | Nam K.,Sunchon National University | Jo C.,Seoul National University | And 2 more authors.
Food Research International | Year: 2016

Proteins and its constituents (amino acids) are known as the major contributors to the off-odor in irradiated meat. However, radiolytic degradation of amino acids occurred not only at side chains but also at amino- and carboxyl-groups of the α-carbon. A model system with amino acid esters was used to elucidate the mechanisms of volatile production at side chains of amino acids by irradiation. The low-molecular weight aldehydes, which contributed to the irradiation off-odor, were mainly from acidic, aliphatic and aliphatic hydroxyl group amino acid esters through the radiolysis of amino acid side chains or Strecker degradation. However, the contribution from non-sulfur amino acids was minor compared with sulfur amino acids. Among the sulfur-containing amino acids, methionine made the greatest contribution to the irradiation off-odor not only through the direct cleavage of the side chain. However, the chemical reactions of sulfur compounds with other compounds produced by irradiation also played significant roles to the off-odor of irradiated meat. © 2015 Elsevier Ltd. Source


Heo C.,Konkuk University | Kim H.W.,Konkuk University | Ko K.Y.,Ministry of Food Drug Safety | Kim K.-T.,Konkuk University | Paik H.-D.,Konkuk University
Journal of Food Safety | Year: 2014

Predictive models to describe the growth of Bacillus cereus in tteokgalbi were developed during storage under various temperatures (5-25C) and inoculation levels (2 and 3 log) to estimate the shelf life. To develop primary models, the observed data were applied to the Baranyi and Gompertz equations. The growth rate was dependent on temperature, but the effect of inoculation level on growth rate was not significant (P>0.05). Thus, the secondary polynomial model was developed as a function of temperature. At 5C, the predicted shelf life of tteokgalbi was approximately 65.5-73.2h. The shelf life at 15 or 25C decreased sharply during storage, and was less than 20h during storage. All primary and polynomial secondary models were characterized by high R2 values, small root mean square error values and very ideal values of Bf and Af. These results present reliable predictive growth models describing the growth of B.cereus under various temperature conditions in tteokgalbi. © 2014 Wiley Periodicals, Inc. Source


Ko K.Y.,Ministry of Food Drug Safety | Park S.R.,Ministry of Food Drug Safety | Lee C.A.,Ministry of Food Drug Safety | Kim M.,Ministry of Food Drug Safety
Journal of Dairy Science | Year: 2015

Nisin, a polypeptide with antimicrobial properties, is known as a natural preservative. It is used in various foods, including dairy products. This study validated a novel procedure using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination of nisin A and nisin Z in cow milk. An extraction solution of 0.1 M acetate buffer containing 1 M NaCl (pH 2.0) and MeOH (1:1) was used to extract nisin A and nisin Z from milk samples. After the addition of extraction buffers, the samples were homogenized and centrifuged. The supernatant was filtered and injected for LC-MS/MS analysis. The linearity of the analytical method had a high correlation coefficient (r. ≥. 0.9987). The limits of quantitation of nisin A and nisin Z were approximately 12.9 and 10.9 μg/kg, respectively. The accuracy of the analytical method in milk ranged from 90.6 to 103.4% for nisin A and from 83.8 to 104.4% for nisin Z. The coefficient of variation values of intra- and interday in milk determined to be less than 5% in both nisin A and nisin Z. Because the proposed method has comparatively high recovery and low coefficient of variation, it seems appropriate for the determination of nisin A and nisin Z in milk samples. As the quantification of nisin A and nisin Z in milk samples by using LC-MS/MS has only been rarely reported until now, this study provides a meaningful technological advance for the dairy industry. © 2015 American Dairy Science Association. Source


Ko K.Y.,Ministry of Food Drug Safety | Park S.R.,Ministry of Food Drug Safety | Lim H.-S.,Ministry of Food Drug Safety | Park S.-J.,Ministry of Food Drug Safety | Kim M.,Ministry of Food Drug Safety
Food Analytical Methods | Year: 2015

The peptide nisin produced by Lactococcus lactis subsp. lactis is known to be one of the natural preservatives that are used in various foods including cheese products. This study optimized and validated a liquid chromatography-tandem mass spectrometry method for determining nisin A and nisin Z in cheese. Processed and natural cheeses were used for method validation. In addition, this study investigated the content of nisin A and nisin Z in 140 cheese samples comprised of imported and domestic cheese. The nisin A and nisin Z contents of 140 cheese samples were determined. An extraction solution consisting of 0.1 M acetate buffer containing 1 M NaCl (pH 2.0) and methanol (NaCl/MeOH, 1:1 v/v) was the optimal solution for nisin extraction from cheese. The limits of quantification of nisin A and nisin Z were approximately 10.2 and 12.6 μg/kg, respectively. For processed cheese and natural cheese, the recoveries were 80.1–107.3 % for nisin A and 74.4–113.9 % for nisin Z and low coefficients of variation. In monitoring study, nisins A and Z were detected in only three soft processed cheese out of 140 samples. The proposed analysis procedure can be used as an efficient tool for determination of nisin A and nisin Z in cheese using liquid chromatography-tandem mass spectrometry (LC-MS/MS). © 2015 Springer Science+Business Media New York Source

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