Sulhee Lee

Bioconversion of Ginsenosides from Red Ginseng Extract Using Candida allociferrii JNO301 Isolated from Meju.

Abstract Red ginseng (Panax ginseng), a Korean traditional medicinal plant, contains a variety of ginsenosides as major functional components. It is necessary to remove sugar moieties from the major ginsenosides, which have a lower absorption rate into the intestine, to obtain the aglycone form. To screen for microorganisms showing bioconversion activity for ginsenosides from red ginseng, 50 yeast strains were isolated from Korean traditional meju (a starter culture made with soybean and wheat flour for the fermentation of soybean paste). Twenty strains in which a black zone formed around the colony on esculin-yeast malt agar plates were screened first, and among them 5 strains having high β-glucosidase activity on p-nitrophenyl-β-D-glucopyranoside as a substrate were then selected. Strain JNO301 was finally chosen as a bioconverting strain in this study on the basis of its high bioconversion activity for red ginseng extract as determined by thin-layer chromatography (TLC) analysis. The selected bioconversion strain was identified as Candida allociferrii JNO301 based on the nucleotide sequence analysis of the 18S rRNA gene. The optimum temperature and pH for the cell growth were 20~30°C and pH 5~8, respectively. TLC analysis confirmed that C. allociferrii JNO301 converted ginsenoside Rb1 into Rd and then into F2, Rb2 into compound O, Rc into compound Mc1, and Rf into Rh1. Quantitative analysis using high-performance liquid chromatography showed that bioconversion of red ginseng extract resulted in an increase of 2.73, 3.32, 33.87, 16, and 5.48 fold in the concentration of Rd, F2, compound O, compound Mc1, and Rh1, respectively.

RAPD typing of Lactobacillus brevis isolated from various food products from Korea

In the present study, the fingerprinting technique, random amplified polymorphic DNA-PCR was evaluated to characterize 13 strains of Lactobacillus brevis, isolated from different vegetable products of South Korea. Two primers i.e. 239 and KAY3 were used. The primer 239 produced bands ranged from 500-4,000 bp and KAY3 primer produced bands with sizes from 600-4,000 bp. Both primers produced thirteen different RAPD profiles. Phylogenetic dendrogram showed that all the isolates could be divided into six major clusters both the primers. However, a few strains of L. brevis had similar profiles and were not well differentiated by RAPD.

Oceanobacillus gochujangensis sp. nov., isolated from gochujang a traditional Korean fermented food

A Gram-stain-positive, polar flagella-containing, rod-shaped, obligate aerobic, endospore-forming bacterium, strain TK1655T, was isolated from the traditional Korean food gochujang. The 16S rRNA sequence of strain TK1655T was a member of the genus Oceanobacillus similar to that of the type strain of Oceanobacillus oncorhynchi subsp. incaldanensis DSM 16557T (97.2%), O. oncorhynchi subsp. oncorhynchi JCM 12661T (97.1%), O. locisalsi KCTC 13253T (97.0%), and O. sojae JCM 15792T (96.9%). Strain TK1655T was oxidase and catalase positive. Colonies were circular, smooth, low convex, cream in colour, and measured about 0.5–1.0 mm in diameter. The range for growth was 20–40°C (optimal, 30°C), pH 6.0–10.0 (optimal, 7.0), and 2–16% (w/v) NaCl (optimal, 2%). Additionally, the cells contained meso-DAP, and the predominant isoprenoid quinone was MK-7. The complex polar lipids were consisted of diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phosphatidylcholine (PC). The major cellular fatty acid components were iso-C15:0, anteiso-C15:0, iso-C16:0, and anteiso-C17:0, and the DNA G+C content was 40.5%. DNA-DNA relatedness of our novel strain and reference strain O. locisalsi KCTC 13253T, O. oncorhynchi subsp. incaldanensis DSM 16557T, O. oncorhynchi subsp. oncorhynchi JCM 12661T was 45.7, 43.8, and 41.9%. From the results of phenotypic, chemotaxonomic, and phylogenetic analyses of strain TK1655T, we propose the novel species Oceanobacillus gochujangensis sp. nov. The type strain is TK1655T (=KCCM 101304T =KCTC 33014T =CIP 110582T =NBRC 109637T).

Semi-Continuous Fermentation of Onion Vinegar and Its Functional Properties

For the fermentation of vinegar using onion, acetic acid bacteria and yeast strains with high fermentation ability were screened. Among them, Saccharomyces cerevisiae 1026 was selected as a starter for ethanol production and Acetobacter orientalis MAK88 was selected as a vinegar producer. When the two-stage fermentation of onion vinegar was performed at 28 °C, the titratable acidity reached 4.80% at 24 h of fermentation. When semi-continuous fermentation proceeded to charge-discharge consisting of three cycles, the acetic acid content reached 4.35% at 48 h of fermentation. At this stage, the fermentation efficiency, acetic acid productivity, and specific product formation rate were 76.71%, 17.73 g/(L·d), and 20.58 g/(g·h), respectively. The process in this study significantly reduced the fermentation time and simplified the vinegar production process. The content of total flavonoids and total polyphenols in onion vinegar were 104.36 and 455.41 μg/mL, respectively. The antioxidant activities of onion vinegar in terms of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic) acid (ABTS+) radical scavenging activity, and reducing power were 75.33%, 98.88%, and 1.28, respectively. The nitrite scavenging abilities of onion vinegar were 95.38 at pH 1.2. The onion vinegar produced in this study showed higher organoleptic acceptability than commercial onion vinegar.

DNA Profiling of Leuconostoc citreum Strains in Fermented Foods by Repetitive Element Polymerase Chain Reaction

To identify and discriminate the bacterial species at the subspecific level, rep-PCR is a reliable genomic fingerprinting tool. Fourteen strains of bacteria were isolated from different food sources, identified as Leuconostoc citreum using 16S rRNA gene sequencing, and amplified using rep-primers (REP, ERIC, and (GTG)5). Fingerprinting patterns generated bands in the range of 300-6,000 bp with REP, 150-6,000 bp with ERIC, and 200-1,700 bp with (GTG)5 primers. In UPGMA dendrogram analysis, 14 strains were clustered into three clades (I, II, and III) with all the primers, thus differentiating them at the molecular level. The present study revealed the differentiation of L. citreum strains using rep-PCR.

Optimization of Oligosaccharide Production from Leuconostoc lactis Using a Response Surface Methodology and the Immunostimulating Effects of These Oligosaccharides on Macrophage Cells

Production of oligosaccharides from Leuconostoc lactis CCK940 was optimized using a response surface methodology with a central composite design. Culture temperature and the concentrations of sucrose and maltose were used as the main factors. The predicted optimum conditions for the production of oligosaccharides were a culture temperature of 30 °C, a sucrose concentration of 9.6% (w/v), and a maltose concentration of 7.4% (w/v). Using these optimal conditions, Leuconostoc lactis CCK940 was cultured using a fermenter to produce oligosaccharides, and the resulting oligosaccharides with a degree of polymerization greater than 4 were purified by Bio-gel P2 gel permeation column chromatography and then lyophilized. When macrophages were treated with the purified oligosaccharides at concentrations of 0.1–10 mg/mL, no cytotoxicity towards the macrophages was observed. However, nitric oxide production levels were similar to those following treatment with 1 μg/mL lipopolysaccharide. The mRNA expression levels of tumor necrosis factor-α, interleukin-1β, interleukin-6, and inducible nitric oxide synthase were all also increased in a dose-dependent manner following treatment with the oligosaccharides. These data suggest that oligosaccharides produced by Leuconostoc lactis CCK940 could be used as an immune enhancer of macrophages.

Molecular typing of Lactobacillus brevis isolates from Korean food using repetitive element-polymerase chain reaction

Lactobacillus brevis is a part of a large family of lactic acid bacteria that are present in cheese, sauerkraut, sourdough, silage, cow manure, feces, and the intestinal tract of humans and rats. It finds its use in food fermentation, and so is considered a “generally regarded as safe” organism. L. brevis strains are extensively used as probiotics and hence, there is a need for identifying and characterizing these strains. For identification and discrimination of the bacterial species at the subspecific level, repetitive element-polymerase chain reaction method is a reliable genomic fingerprinting tool. The objective of the present study was to characterize 13 strains of L. brevis isolated from various fermented foods using repetitive element-polymerase chain reaction. Repetitive element-polymerase chain reaction was performed using three primer sets, REP, Enterobacterial Repetitive Intergenic Consensus (ERIC), and (GTG)5, which produced different fingerprinting patterns that enable us to distinguish between the closely related strains. Fingerprinting patterns generated band range in between 150 and 5000 bp with REP, 200–7500 bp with ERIC, and 250–2000 bp with (GTG)5 primers, respectively. The Jaccard’s dissimilarity matrices were used to obtain dendrograms by the unweighted neighbor-joining method using genetic dissimilarities based on repetitive element-polymerase chain reaction fingerprinting data. Repetitive element-polymerase chain reaction proved to be a rapid and easy method that can produce reliable results in L. brevis species.

Analysis of Leuconostoc citreum strains using multilocus sequence typing

The objective of this study was to perform genetic diversity analysis of 13 strains isolated from South Korean foods by multilocus sequence typing (MLST). For typing, seven housekeeping loci (atpA, dnaA, dnaK, gyrB, pheS, pyrG, and rpoA) were selected, amplified and analyzed. Fifty-one polymorphic sites varying from 1 to 22 in each species were identified. Thirteen sequence types were generated with allele numbers ranged from 2 to 10. The overall relationship between strains was assessed by unweighted pair group method with arithmetic mean dendrogram and minimum spanning tree. In addition, combined spits tree analysis revealed intragenic recombination. No clear relationship was observed between the isolation sources and strains. The developed MLST scheme enhanced our knowledge of the population diversity of Leu. citreum strains and will be used further for the selection of industrially important strain.

DNA profiling of Leuconostoc mesenteroides strains isolated from fermented foods and farm produce in Korea by repetitive-element PCR

Lactic acid bacteria are known for their preservative effects on food products like meat and sausage. Since they are related to humans, these bacteria require proper characterization and identification among various other bacteria in the surroundings. For their identification, several typing methods have already been applied of which the genotyping methods provide reproducible and unambiguous results. In this study, PCR-based method called repetitive element PCR was used for typing 37 Leuconostoc mesenteroides with three primers, REP, ERIC, and (GTG)5, annealing to repetitive sequences present in the bacterial genome. Different fingerprints were obtained for the isolates showing distinguishing profiles. Further phylogenetic analysis was performed using UPGMA method of clustering which provided proper identification with genetic relatedness of all the isolates. It was finally observed that, out of the three primers used, (GTG)5 discriminated the strains precisely than the other two.

Fed–batch fermentation of onion vinegar using Acetobacter tropicalis

To produce onion vinegar with high efficiency, various fermentation conditions, such as varying initial ethanol concentrations and the addition of ethanol or onion juice were optimized. Acetobacter tropicalis KFCC 11476P consumed ethanol at a rate of 0.125–0.140 g/h when the initial ethanol concentrations were 4, 5, and 6%, and the acidity of the fermentation broth reached the maximum level when the ethanol was completely starved. In the case of fed-batch fermentation with continuous feeding, when a small amount of ethanol and onion juice was continuously supplied into the broth after 30 h of fermentation, the acidity continued to increase up to 4.5% at 45 h. All the while, the remaining ethanol content of the fermentation broth was 1.13-1.69%. The maximum acidity of onion vinegar in the pilot–scale fermenter reached 4.6% at 48 h of which fermentation speed was five times faster than the general standard.