• Microbiology and Biotechnology Letters
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• v.22 no.3
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• pp.259-265
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• 1994

A bacteriocin-producing lactic acid bacteria was isolated from contaminated milk products, which was identified by using the API50 CH kit as Lactococcus lactis subsp. lactis with reliability of 98%. Fatty and analysia of the cell membrane showed that this strain contained same fatty acids profiles as type strain, Lactococcus lactis subsp. lactis ATCC 19435. The bacteriocin of Lactococcus sp. HY 449 showed relatively wide range of inhibition spectrum against gram positive and some gram negative bacteria such as Escherichia coli and maintained the inhibitory activity between pH2.0 and pH9.0 The thermostability of this bacteriocin was higher in acidic solution than in distilled water and was stable at 60$\circ $C for 1 hour.

• Journal of Microbiology and Biotechnology
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• v.6 no.2
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• pp.137-141
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• 1996

Acetoin and ammonia, the precursors of tetramethylpyrazine (TMP) having "meaty" or "roasted" flavors, were produced by the culture of Lactococcus lactis ssp. lactis biovar. diacetilactis FC1 in free and immobilized cell systems. Cells were immobilized using k-carrageenan and then were incubated at $34^{\circ}C$. The TMP productivity (0.34 g/l) and the conversion ratio (9.3%) of acetoin to TMP of the immobilized cell system were higher than those (0.24 g/l, 7.0%) of the free cell system. When the beads were activated for 12 h, the productivity of acetoin and TMP increased slightly.

• Journal of Microbiology and Biotechnology
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• v.1 no.3
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• pp.202-206
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• 1991

To produce acetoin as a precursor of the tetramethylpyrazine flavor compound from citrate by Lactococcus lactis ssp. lactis biovar. diacetilactis FC1, fermentation factors such as inital pH of culture media, temperature, concentration of Na-citrate, thiamin-HC1 and sugars were examined. The best acetoin production was achieved with initial pH in the culture media of 5.5, fermentation temperature of $34^{\circ}C$, Na-citrate concentration of 3%, addition of thiamin-HC1 at 2 mg/l and galactose as a carbon source. When fermentation was carried out under the optimum conditions, the exhaustion of Na-citrate and the production of acetoin took simultaneously and acetoin reached the maximum content, 80 mmole/l after 20 hours.

• Journal of Microbiology and Biotechnology
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• v.30 no.9
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• pp.1404-1411
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• 2020

Lactic acid bacteria (LAB) play an important role in dairy fermentations, notably as cheese starter cultures. During the cheese production and ripening period, various enzymes from milk, rennet, starter cultures, and non-starter LABs are involved in flavor formation pathways, including glycolysis, proteolysis, and lipolysis. Among these three pathways, starter LABs are particularly related to amino acid degradation, presumably as the origins of major flavor compounds. Therefore, we used several enzymes as major criteria for the selection of starter bacteria with flavor-forming ability. Lactococcus lactis subsp. lactis LDTM6802 and Lactococcus lactis subsp. cremoris LDTM6803, isolated from Korean raw milk and cucumber kimchi, were confirmed by using multiplex PCR and characterized as starter bacteria. The combinations of starter bacteria were validated in a miniature Gouda-type cheese model. The flavor compounds of the tested miniature cheeses were analyzed and profiled by using an electronic nose. Compared to commercial industrial cheese starters, selected starter bacteria showed lower pH, and more variety in their flavor profile. These results demonstrated that LDTM6802 and LDTM6803 as starter bacteria have potent starter properties with a characteristic flavor-forming ability in cheese.

• Journal of Microbiology and Biotechnology
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• v.10 no.4
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• pp.539-543
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• 2000

A new bacteriocin, named lacticin 10790, was purified from Lactococcus lactis subsp. cremoris KFCC 10790 by sequential adsorption, immobilized metal-affinity, cation-exchange, and $C_{18}$ reverse-phase chromatographies. The molecular mass of the bacteriocin was estimated to be between 3,000 and 3,500 Da. Lacticin 10790 showed a broad antimicrobial spectrum against many gram-positive bacteria. The bacteriocin was stable to heat and in the pH range between 2 and 6. Lacticin 10790 was destroyed by digestion with proteases and exhibited a bactericidal mode of action. An amino acid composition analysis of purified lacticin 10790 revealed a high concentration of hydrophobic amino acids. The N terminus of the bacteriocin was found to be blocked, upon analysis by Edman degradation. The results suggest that lacticin 10790 is a class I bacteriocin.

• Microbiology and Biotechnology Letters
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• v.21 no.4
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• pp.293-298
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• 1993

The ppage resistance mechanism of Lactococcus lactis subsp. cremoris ATCC 11602-A1 was investigated. When parent and A1 were incubated at 30 and 40$^{\circ}C$, A1 grew well and multiplication of phage(MOI=1)on A1 slightly occurred at 40$^{\circ}C$ in contrast with parent. There was a great difference of proteolytic activity between parent and A1, irrespective of the temperature. As a result of ADS treatment oon culture broth, survival rate of A1 was 27% at the lethal concentration of parent and adsorption rate of phage was increased to 95~97%, which was considered to come from the exposure of phage receptor site masked by an unknown component. These results suggest that acridine orange (AO) treatment leads to the modification of cell wall, conferring resistance to high temperature and lytic phage. No change in plasmid profiles of A1 at 30 and 40$^{\circ}C$ were found, which suggests that plasmid is not relative to temperature-resistance of A1.

• Microbiology and Biotechnology Letters
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• v.46 no.2
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• pp.91-101
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• 2018

The aim of this study was to transfer the 18.5 kb gene clusters coding for 17 genes from Lactobacillus rhamnosus to Lactococcus lactis subsp. cremoris MG1363 in order to determine the effect of host on exopolysaccharide (EPS) production and to provide a model for studying the phosphorylation of proteins which are proposed to be involved in EPS polymerization. Lactobacillus rhamnosus RW-9595M and ATCC 9595 have 99% identical operons coding for EPS biosynthesis, produced different amounts of EPS (543 vs 108 mg/l). L. lactis subsp. cremoris MG1363 transformed with the operons from RW-9595M and ATCC 9595 respectively, produced 326 and 302 mg/l EPS in M17 containing 0.5% glucose. The tyrosine protein kinase transmembrane modulator (Wzd) was proposed to participate in regulating chain elongation of EPS polymers by interacting with the tyrosine protein kinase Wze. While Wzd was found in phosphorylated form in the presence of the phosphorylated kinase (Wze), no phosphorylated proteins were detected when all nine tyrosines of Wzd were mutated to phenylalanine. Lactococcus lactis subsp. cremoris could produce higher amounts of EPS than other EPS-producing lactococci when expressing genes from L. rhamnosus. Phosphorylated Wzd was essential for the phosphorylation of Wze when expressed in vivo.

• Microbiology and Biotechnology Letters
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• v.41 no.4
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• pp.391-397
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• 2013

A putative cyclomaltodextrinase (LLCD) gene was cloned from the genome of Lactococcus lactis subsp. lactis KCTC 3769 (ATCC 19435), which encodes 584 amino acids with the predicted molecular mass of 68.7 kDa. KCTC 3769 shares approximately 40% of amino acid sequence identity with the CDase-family of enzymes. The dimeric enzyme with C-terminal six-histidines was heterologously expressed and purified from recombinant E. coli. LLCD showed the highest activity against ${\beta}$-cyclodextrin (CD) at pH 7.0 and $37^{\circ}C$. In particular, LLCD exhibited extremely low activity against starch and pullulan, while its CD-hydrolyzing activity was about 80 times higher than starch. Due to its much higher activity on CD over starch, LLCD has been identified as a member of CDases. However, LLCD can be distinguished from the other common CDases on the basis of its extremely low hydrolyzing activity against starch, pullulan, and acarbose.

• Journal of Microbiology and Biotechnology
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• v.6 no.1
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• pp.50-53
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• 1996

A cultured milk product was made by fennenting 10$\%$ reconstituted skim milk with Lactococcus lactis subsp. lactis TA29 and Saccharomyces exiguus SK2. L. lactis TA29 and S. exiguus SK2 grew up to 1.0 $\times 10^9\;and\;2.0 \times 10^6$ cfu/ml, respectively. After the fermentation 21$\%$ of lactose was hydrolyzed, pH was lowered to 4.2, and titratable acidity and alcohol concentration were increased to 0.96 and 0.023$\%$, respectively. When the fermented milk was stored at $4{\circ}C$ for 9 days, the viable cell counts for L. lactis TA29 and S. exiguus SK2 were $6.5 \times 10^5\;and\;1.6 \times 10^6$ cfu/rnl, respectively. The alcoholic fermented milk prepared in this experiment was more inhibitory against some pathogenic bacteria including C. perfringens than commercial yoghurt products tested.

• Journal of the Korean Society of Food Science and Nutrition
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• v.41 no.8
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• pp.1066-1071
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• 2012

In this study we investigated the change in antigenicity and allergenicity of Meju, a traditional Korean soybean product, by fermentation via 3 different microorganisms. The steamed soybeans were fermented with Lactococcus lactis subsp. lactis and/or Aspergillus oryzae and/or Bacillus subtilis. Proteins in soybean were degraded after fermentation. Antigenicity or allergenicity were analysed by immunoblotting and ELISA using soybean protein-specific polyclonal antibodies or soybean allergic patient sera. The best degradation was achieved by three step fermentation using nisin-producing Lactococcus lactis subsp. lactis IFO12007, A. oryzae and B. subtilis. Allergenicity and antigenicity were also starkly reduced after three step fermentation. The three-step fermentation method developed in our lab suggests an excellent alternative to reduce the allergenicity of soybeans.