• Korean Journal of Food Science and Technology
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• v.29 no.3
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• pp.546-554
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• 1997

Gel-type yogurt was prepared from egg white powder (3%, w/v), glucose (2%, w/v) and four kinds of milk products (4%, w/v). The effects of milk product on acid production and growth of Lactobacillus were studied. The effects of milk product on sensory property and volatile aroma compounds were also studied. Acid production by L. acidophilus at 24 hr in samples containing milk product was significantly lower than that by L. acidophilus in milk (p<0.05). The sample containing casein produced less acid than the other samples. Number of viable cells of L. acidophilus at 24 hr in milk and samples containing milk product was $2.0{\times}10^{9}/mL$ and $5.0{\times}10^{8}{\sim}8.0{\times}10^{8}/mL$, respectively. Sensory property of the samples containing milk product was lower than that of milk yogurt (reference). However, sensory property of the sample containing casein was not significantly different from that of milk yogurt (p<0.05). The sample containing whey powder showed lower sensory score than other samples. Though the composition of volatile aroma compounds was slightly different from sample to sample, gas chromatographic analysis detected acetone, ethanol, diacetyl and acetoin in samples fermented by L. acidophilus.

• Journal of Environmental Health Sciences
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• v.28 no.1
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• pp.21-29
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• 2002

To identify and evaluate the dichlorobenzidine(DCB)-DNA adducts in liver cell and bladder epithelial cells by $^{32}$ P-postlabeling and GC/MS-SIM, we orally exposed the dichlorobenzidine(20mg/kh body wt./day) to male Sprague-Dawley rats(l85$\pm$10g) for 14 days. Two kinds of DCB-DNA adduct(A1 and A2) were found at the same site of thin layer chromatogram of $^{32}$ P-postlabeling method in liver cells and bladder epithelial cells. In liver cells, relative adduct labeling(RAL) $\times$ 10$^{12}$ of DCB-DNA adduct A1 were 34.1$\pm$3.71 and 69.9$\pm$5.02, that of adduct A2 were 74.1$\pm$10.1 and 105.1$\pm$10.1 on 10 and 14 days after treatment, respectively. And in bladder epithelia cells, RAL $\times$ 10$^{12}$ of DCB-DNA adduct A1 were 5.92$\pm$1.60 and 15.9$\pm$1.31, that of adduct A2 were 9.81$\pm$2.81 and 22.8$\pm$1.79 on 10 and 14 days after treatment, respectively. DCB metabolites formed DNA adducts were monoacetyl-dichlorobenzidine(acDCB) and diacetyl-dichlorobenzidine(di-acDCB), which was identify by gas chromatography/mass spectrometry-scan ionization mode(GC/MS-SIM), after hydrolysis of DCB-DNA adducts isolated from live cells and bladder epithelial cells. The base peak of acDCB were 252 and 294 m/z, and that of di-acDCB were 252, 294 and 336 m/z. In conclusion, the exposed DCB formed two kinds of DCB-DNA adduct, the proximate materials of that were acDCB and di-acDCB in liver and bladder epithelial cells. And the above GC/MS-SIM method was found the DCB-DNA adducts could be monitoring by gas chromatography.

• KSBB Journal
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• v.15 no.5
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• pp.438-443
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• 2000

Continuous processes using immobilized yeast were investigated in order to shorten beer maturation time. Three silica-based ceramic media and one cellulose-based medium were used. Diacetyl (DA) was one of the most distinctive compounds causing immature flavors. Heat treatment of green beer (GB) to convert a-acetolactate to DA was essential to shorten the time for beer maturation. The longer heat treatment time was needed at the lower temperature. Oxygen concentration in GB had a large influence on the conversion of a-acetolactate to DA. The lower the oxygen concentration in GB, the lower conversion ratio to DA. Heat treated GB was fed continuously to four kinds of immobilized yeast columns. DA concentration after immobilization columns was reduced to less than 0.1ppm at $3∼5^{\circ}C$ 180∼150 minutes retention time in all columns tested. This concentration is enough to fit the quality speification of commercialized product. Formation of a-acetolactate from residual sugars was higher in ceramic media column than cellulose media cloumn. The taste of beers from test processes were not the same as that of traditionally produced beer, but no off-flavors were detected in test samples, which shows that immobilized yeast columns have potentials as rapid processes for beer maturation.

• Journal of Life Science
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• v.12 no.1
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• pp.77-86
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• 2002

Chitin, a $\beta$-1,4 polymer of N-acetyl-D-glucosamine, is one of the most abundant organic compounds in nature. Chitinase (EC 3.2.1.14) is an enzyme that degrades chitin to chito-oligosaccharides, diacetyl rhitobiose and N-acetyl-D-glucosamine. An extracellular chitinase-producing bacterial strain was isolated from soil and named to as Bacillus subtilis JK-56. Optimum culture condition of B. subtilis JK-56 for the production of chitinase was 1% chitin, 0.5% polypepton, 0.1% KCl, 0.05% MnS $O_4$.4$H_2O$, 37$^{\circ}C$, initial pH 7.0 and 40 hour culture time. When B. subtilis JK-56 was grown in the optimum medium, one major active band and two minor active bands were detected by native-PAGE and active staining of the gel. Among them, the major band was purified from the culture supernatant by 70% ammonium sulfate precipitation and native-PAGE with BIO-RAD Model 491 Prep-Cell and named as Chi-56A. Its molecular weight was estimated to be 53kDa monomer and the isoelectric point (pI) was pH 4.3. The pH and temperature for the optimum activity of Chi-56A were pH 6.0 and $65^{\circ}C$, respectively. Chi-56A was stable up to $65^{\circ}C$ and in alkaline region. Its $K_{m}$ value for colloidal chitin was 17.33g/L. HPLC analysis of the reaction products confirmed that Chi-56A was an exo type chitinase.e.

• Korean journal of food and cookery science
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• v.12 no.2
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• pp.153-161
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• 1996

A curd yogurt was prepared from egg white powder (EWP) and casein added with sugars (glucose, fructose, lactose). The effects of sugar addition on acid production and growth of Lactobacillus were studied. The effects of sugar addition on sensory property and volatile aroma compounds were also studied. Acid production by L. acidophilus in EWP 2％ (W/V), casein 3％ (w/v) and sugar 0.5,1 or 2％ W/V) was lower than that of L. acidophilus in milk (control). Acid production in sample added with glucose or fructose of 1％ or 2% (W/V) was higher than that of 0.5% (W/V), while acid production in lactose added sample was not affected with the concentration of lactose. Number of viable cells of L. acidophilus at 24 hr in milk, glucose added sample, fructose added sample and lactose added sample was 3.6${\times}$10/Sup 9/, 5.6${\times}$10$\^$8/, 6.0${\times}$10$\^$8/,and 3.2${\times}$10$\^$7/, respectively. Through 30hr fermentation, acid production and number of viable cells of L. acidophilus in milk were higher than those of sugar added samples. Sensory property of fructose added sample was slightly better than that of milk yogurt (reference), while that of lactose added sample was significantly inferior. Though the composition of volatile aroma compounds was slightly different according to sample, gas chromatographic analysis detected acetone, ethanol, diacetyl and acetoin in samples fermented by L. acidophilus.

• Korean Journal of Food Science and Technology
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• v.33 no.5
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• pp.603-610
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• 2001

The quality characteristics of soy yogurt prepared with different proteolytic enzymes and starter culture were evaluated. In order to facilitate the growth of lactic acid bacteria and subsequent production of lactic acid, soy protein isolate(SPI) was hydrolyzed using three kinds of proteases; one extracted from Aspergillus oryzae, bromelain and ${\alpha}-chymotrypsin$. The cultural systems employed thereafter for lactic fermentations were: 1) Bifidobacterium bifidum, 2) B. bifidum and Lactobacillus acidophilus, 3) B. bifidum and Lactobacillus bulgaricus. In soy yogurt, pH was more decreased by mixed culture method than single culture method with the accumulation of lactic acid. Viable cells of lactic acid bacteria in soy yogurts were measured $10^8$ CFU/g by the single culture method while $10^9$ CFU/g by the mixed culture method except ${\alpha}-chymotrypsin$ treatment. The amount of free amino acids in soy yogurts were substaintially increased by enzyme treatment. Viscosity was decreased by enzyme treatment, resulting in higher viscosity by ${\alpha}-chymotrypsin$ treatment. Water holding capacity was found to be higher in the single culture method in case of enzyme treatment. Among the various volatile flavor components isolated and identified after enzyme hydrolysis, acetaldehyde, ethanol, diacetyl, butyl alcohol contents tended to increase by lactic fermentation.

• Food Science and Biotechnology
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• v.17 no.3
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• pp.679-682
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• 2008

A lactic acid bacterium producing an antimicrobial substance against Escherichia coli O157:H7 was isolated from raw milk and identified as Lactobacillus amylovorus ME-1. In addition to E. coli O157 :H7, the antimicrobial substance also inhibited the growth of Bacillus cereus, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella typhimurium, Staphylococcus aureus, Streptococcus agalactiae, Streptococcus pyrogenes, and Yersinia enterocolitica. The antimicrobial substance was stable at pH 2-12 and $121^{\circ}C$ for 15 min and insensitive to proteinase K, protease, amylase, and catalase. Purification of the antimicrobial substance was conducted through methanol and acetonitrile/ethylacetate extraction, ultrafiltration with a 500 Da cutoff, thin layer chromatography (TLC) with silicagel 60, and high performance liquid chromatography (HPLC) with a $C_{18}$ reverse phase column. The ${\lambda}_{max}$ of the purified antimicrobial substance was determined as 192 nm by ultra violet (UV) scanning, while the molecular weight was estimated as 453 Da based on the mass spectrum. Accordingly, the current results suggest that the antimicrobial substance from the L. amylovorus ME-1 was not a bacteriocin, but rather a new non-proteinaceous substance distinct from acidophilin, acidolin, diacetyl, and reuterin.

• Food Science of Animal Resources
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• v.38 no.1
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• pp.110-122
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• 2018

Akcakatik cheese (yogurt cheese) is produced by drying strained yogurt with or without adding cloves or black cumin. The main objective of this study was to detect the properties of both fresh and ripened Akcakatik cheeses and to compare them. For this purpose the biogenic amine content, volatile flavor compounds, protein degradation level, chemical properties and some microbiological properties of 15 Akcakatik cheese samples were investigated. Titratable acidity, total dry matter, NaCl, total nitrogen, water soluble nitrogen, ripened index, histamine, diacetyl and acetaldehyde levels were found to be higher in ripened cheese samples than in fresh cheese samples. On the other hand, the clove and black cumin ratios were found to be higher in the fresh cheese samples. Sodium dodecyl sulphate polyacrylamide gel electropherograms of cheese samples showed that protein degradation was higher in ripened cheese samples than in fresh samples, as expected. The dominant Lactic acid bacteria (LAB) flora of Akcakatik cheese samples were found to be Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.

• Food Science of Animal Resources
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• v.38 no.5
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• pp.1008-1018
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• 2018

Although bacteriocins with anti-listerial activity have been isolated from a wide variety of lactic acid bacteria, little is known about those from Leuconostoc lactis, a heterofermentative bacterium that produces diacetyl and exopolysaccharides in dairy foods. In this study, an anti-listerial bacteriocin was isolated from Leuc. lactis SD501 and characterized. It was particularly potent against Listeria monocytogenes and also inhibited Enterococcus faecalis. Anti-listerial activity reached a maximum during the early stationary phase and then decreased gradually. The anti-listerial substance was sensitive to proteinase K and ${\alpha}$-chymotrypsin, confirming its proteinaceous nature. Its activity remained stable at pH values ranging from 1 to 10. In addition, it was strongly resistant to high temperatures, retaining its activity even after incubation for 15 min at $121^{\circ}C$. The apparent molecular mass of the partially purified anti-listerial bacteriocin was approximately 7 kDa. The characteristics of the SD501 bacteriocin, including its small molecular size (<10 kDa), strong anti-listerial activity, wide pH stability and good thermostability, indicate its classification as a Class IIa bacteriocin.

• The Korean Journal of Pesticide Science
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• v.5 no.1
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• pp.24-29
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• 2001

This study was conducted to investigate insecticidal activities of Ginkgo biloba (L.) leaves-derived bilobalide and its hydrolysis and oxidation products against adults of Nilaparavata lugens Stal. To find out active insecticidal moiety of bilobalide, decomposed intermediates and derivatives of bilobalide were made by hydrolysis, oxidation, and acetylation. The structures of hydrolysis product by base and oxidation product by acid were identified as cyclopentenone analogues and trilactone sesquiterpene from dehydration of bilobalide, respectively. Insecticidal activities of the decomposed intermediates and the derivatives of bilobalide decreased in the order of bilobalide, monoacetate, ginkgolide C, oxidation product, diacetate, and hydrolysis product. Therefore, trilactone structure of bilobalide may be essential for its insecticidal activity.