• Journal of Life Science
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• v.25 no.2
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• pp.174-179
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• 2015

The presence of psychrotrophic bacteria downgrades the quality of dairy products. This study evaluated the effect of lipolytic psychrotrophic bacteria on the chemical properties of Gouda cheese made from raw milk experimentally inoculated with a psychrotrophic bacterium (Acinetobacter genomospecies 10). Raw milk experimentally inoculated with Acinetobacter genomospecies 10 and refrigerated at $4^{\circ}C$ for 3 or 6 days produced a 6-week ripened Gouda cheese with a significant decrease in total solids (p<0.05) or an increased fat content (p<0.05), respectively. Raw milk inoculated with Acinetobacter genomospecies 10 and refrigerated for 3 days had higher (p<0.05) SCFFA (1.35 times), MCFFA (1.42 times), and LCFFA (1.44 times) than the control 6-week ripened Gouda cheese. The cheese manufactured from the inoculated and refrigerated raw milk had higher (p<0.05) total free fatty acids (1.68 times) compared with the control. Raw milk inoculated with Acinetobacter genomospecies 10 and refrigerated for 6 days had increased SCFFA (1.45 times), MCFFA (1.28 times), and LCFFA (1.38 times) compared with the control 6-weeks ripened Gouda cheese. The 6-week ripened Gouda cheese manufactured from this inoculated milk had higher (p<0.05) total free fatty acids (1.34 times) compared with the control. The results indicated that the production of excessive free fatty acids in dairy products by psychrotrophic bacteria can be critical in predisposing dairy products to off-flavors and in turn degrading their quality.

• Food Science of Animal Resources
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• v.33 no.4
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• pp.542-548
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• 2013

This study was conducted to investigate effect of psychrotrophic bacteria on the quality of raw milk. Acinetobacter genomospecies 10 was selected as lipolytic species, and Serratia liquefaciens as proteolytic species. Lipase present in inoculated raw milk with Acinetobacter genomospecies 10 did not affect total solid and fat contents. However, the free fatty acid (FFA) content, especially short chain FFAs, of milk with Acinetobacter genomospecies 10 was dramatically increased. FFAs produced by lipolysis of milk fat are important in flavor of dairy products, excessive lipolysis occurring in milk and dairy products could cause off-flavor, and produced FFAs may have an underiable effect on their flavor. In addition, protease influenced the quality of inoculated raw milk with Serratia liquefaciens. In degradation patterns of casein by SDS-PAGE analysis from inoculatred raw milk with Serratia liquefaciens, casein content was gradually decreased during storage at $4^{\circ}C$, and extensive degradation of $\kappa$-casein was observed on the storage day of 13. The free amino acids such as leucine, valine, arginine, and tyrosine were dramatically increased, which causes bitter taste in raw milk. These excessive peptides in dairy products, produced by psychrotrophic bacteria, can be possible to develop off-flavors and be responsible for gelling of milk by degradation.

• Food Science of Animal Resources
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• v.34 no.4
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• pp.543-551
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• 2014

The aim of this study was to evaluate the effect of proteolytic (Serratia liquefaciens, match %: 99.39) or lipolytic (Acinetobacter genomospecies 10, match %: 99.90) psychrotrophic bacteria (bacterial counts, analysis of free fatty acids (FFA) and analysis of free amino acids) on the microbial and chemical properties (yogurt composition), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of yogurt during storage. Yogurts were prepared with raw milk preinoculated with each psychrotrophic bacteria. The total solid, fat, and protein content were not affected by preinoculation, but the pH of yogurt preinoculated with psychrotrophic bacteria was higher than in control. There was a dramatic increase in short chain free fatty acids among FFA in yogurt with Acinetobacter genomospecies 10. For 14 d of cold storage condition, SCFFA was 25.3 mg/kg to 34.4 mg/kg (1.36 times increased), MCFFA was 20.4 mg/kg to 25.7 mg/kg (1.26 times increased), and LCFFA was 240.2 mg/kg to 322.8 mg/kg (1.34 times increased). Serratia liquefaciens (match %: 99.39) in yogurt caused a greater accumulation of free amino acids (FAA), especially bitter peptides such as leucine, valine, arginine, and tyrosine, but SDS-PAGE showed that the inoculation of Serratia liquefaciens did not affect the degree of casein degradation during storage. Taken together, the excessive peptides and FFA in yogurt generated from psychrotrophic bacteria could develop off-flavors that degrade the quality of commercial yogurt products.

• Korean Journal of Clinical Laboratory Science
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• v.51 no.4
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• pp.444-452
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• 2019

Carbapenem resistance, mediated by the major acquired metallo-β-lactamase (MBL) genes, has been increasingly reported, particularly for clinical isolates of Acinetobacter spp. Of the 191 nonduplicate clinical isolates of the carbapenem-nonsusceptible Acinetobacter spp. evaluated, 125 isolates (65.4%) were positive for the modified imipenem or meropenem-Hodge test, and 49 isolates (25.7%) were positive for the imipenem-EDTA+SMA double disk synergy test (DDS). PCR and sequencing of the bla_VIM-2-allele and bla_IMP-1-allele showed that 29 A. baumannii isolates and 1 A. calcoaceticus isolate had bla_VIM-2, whereas 16 A. baumannii isolates and 2 A. calcoaceticus isolates had bla_IMP-6; 1 isolate of the A. genomospecies 3 had bla_VIM-2 and bla_AIM-1. All the above MBL genes belong to class 1 integron. The size of class 1 integron encompassing bla_VIM-2 or bla_IMP-6 ranges from 2.8 kb to 3.2 kb in clinical isolates of A. baumannii, and 3.2 kb to 3.5 kb in clinical isolates of A. genomospecies 3. bla_VIM-2 was most often located first or second in the class 1 integron, and these integrons often included aacA4. Due to dispersion of the MBL-producing Acinetobacter spp. as well as integron, which may encompass various resistance genes, there is an expectation for the increase of multidrug resistant Gram-negative bacteria, including resistance of carbapenems such as imipenem or meropenem. Hence, the development of new antimicrobial agents for treating severe Acinetobacter spp. infections is needed.

• Food Science of Animal Resources
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• v.33 no.6
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• pp.772-780
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• 2013

The aim of this study was to investigate the effect of season and location on activities of enzyme produced by psychrotrophic bacteria isolated from raw milk located in Kyunggi region of South Korea. Agar diffusion and colorimetric methods were used for the lipase and protease activities of psychrotrophic bacteria. Intensities of dark blue and transparent ring around colony were compared for activity measurement. Nutrient agar with 1% skim milk added was employed for measuing protease activity. 14 strains of Arthrobacter russicus with lipase activity and 19 strains of Chryserobacterium shigense with protease activities were found to be present. It was found that Acinetobacter genomospecies 10 (match %: 99.90) isolated from B region in fall was the most lipolytic species, whereas Serratia liquefaciens (match %: 99.39) isolated from the same region in spring was the most proteolytic species. Growth curve of Acinetobacte and Serratia liquefaciens was a typical sigmoidal form. Lipase activity increased with incubation time, but its activity began to drop at stationary to motality phase. Optimum condition for incubation time, pH and temperature for extracellular lipase from Acinetobacter genomospecies 10 (match %: 99.90) was 12 h, 8.5, and $45^{\circ}C$, respectively. Extracellular protease from Serratia liquefaciens (match %:99.39) had the same optimum incubation time and pH as extracellular lipase, but optimum temperature was $35^{\circ}C$.