Chan-Ick Cheigh

Antagonism of Helicobacter pylori by bacteriocins of lactic acid bacteria

Antimicrobial activity of seven bacteriocins produced by lactic acid bacteria against Helicobacter pylori strains (ATCC 43504, Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH [DSM] 4867, DSM 9691, and DSM 10242) was investigated in vitro using a broth microdilution assay. The bacteriocins chosen for the study were nisin A; lacticins A164, BH5, JW3, and NK24; pediocin PO2; and leucocin K. Antimicrobial activity of the bacteriocins varied among the H. pylori strains tested, of which strain ATCC 43504 was the most tolerant. Among the bacteriocins tested, lacticins A164 and BH5 produced by Lactococcus lactis subsp. lactis A164 and L. lactis BH5, respectively, showed the strongest antibacterial activity against H. pylori strains. MICs of the lacticins against H. pylori strains, when assessed by the critical dilution micromethod, ranged from 0.097 to 0.390 mg/liter (DSM strains) or from 12.5 to 25 mg/liter (ATCC 43504), supporting the strain-dependent sensitivity of the pathogen. Pediocin PO2 was less active than the lacticins against four strains of H. pylori, and leucocin K was the least active peptide, with no inhibition toward H. pylori ATCC 43504. Anti-Helicobacter activity of lacticin A164 was dependent on initial inoculum size as well as concentration of the bacteriocin added.

Weissella kimchii sp. nov., a novel lactic acid bacterium from kimchi.

A gram-positive, catalase-negative, non-sporulating, facultatively anaerobic, short rod-shaped bacterium, with cells measuring 0.3-0.5 x 1-2 microm and designated strain CHJ3T, was isolated from partially fermented kimchi, a traditional Korean fermented vegetable food. The strain produced CO2 gas, D-lactate from glucose and dextran from sucrose and hydrolysed aesculin and arginine. It also fermented N-acetylglucosamine, amygdalin, arbutin, cellobiose, D-fructose, galactose, beta-gentiobiose, gluconate, D-glucose, maltose, D-mannose, salicin, sucrose and D-xylose. The G+C content of the DNA was 48.2 mol%. Phylogenetic analysis of 16S rRNA showed that strain CHJ3T is a member of the genus Weissella. The nearest phylogenetic relative of strain CHJ3T was Weissella confusa, with 16S rRNA similarity of 98.3%. However, strain CHJ3T could be differentiated from W. confusa on the basis of some phenotypic characteristics, analysis of whole-cell protein patterns and DNA-DNA hybridization data. These data suggest that strain CHJ3T be classified in the genus Weissella as a novel species, Weissella kimchii sp. nov. The type strain is CHJ3T (= KCCM 41287T = DSM 14295T = KCTC 3746T).

Optimization of subcritical water extraction of flavanols from green tea leaves.

The subcritical-water extraction (SWE) of six kinds of flavanols from green tea leaves and the effect of extraction conditions were investigated by varying the temperature and time. The maximum yield of total flavanols, 71.36 ± 4.23 mg/g green tea leaves (mean ± SD), was obtained under extraction temperature/time conditions of 150 °C/5 min. The efficiency of SWE for total flavanols was slightly higher than that of the conventional extraction solvents such as methanol and ethanol. The extraction of flavanols via SWE was specifically adequate for epimer structures such as catechin, catechin gallate, and gallocatechin gallate due to the epimerization of epicatechins. The extraction efficiency of epimers was increased at temperatures up to 170 °C, whereas that of epicatechins was decreased. Thus, most epicatechins were converted to epimers during SWE, leading to some flavanol destruction at high temperatures, except when a short extraction time of 5 min was used.

Optimization of processing conditions for the sterilization of retorted short-rib patties using the response surface methodology

The aim of this study was to determine the optimum sterilization conditions for short-rib patties in retort trays by considering microbiological safety, nutritive value, sensory characteristics, and textural properties. In total, 27 sterilization conditions with various temperatures, times, and processing methods were tested using a 3(3) factorial design. The response surface methodology (RSM) and contour analysis were applied to find the optimum sterilization conditions for the patties. Quality attributes were significantly affected by the sterilization temperature, time, and processing method. From RSM and contour analysis, the final optimum sterilization condition of the patties that simultaneously satisfied all specifications was determined to be 119.4°C for 18.55min using a water-cascading rotary mode. The findings of the present study suggest that using optimized sterilization conditions will improve the microbial safety, sensory attributes, and nutritional retention for retorted short-rib patties.

Sporicidal Activities of Various Surfactant Components against Bacillus subtilis Spores.

The sporicidal activities against Bacillus subtilis spores of surfactant components with hydrophilic and hydrophobic properties that can lead to the denaturation of various proteins comprising the spore structure were investigated. The reduction in spore numbers by each of the surfactant components bornyl acetate, geranyl acetate, pinene, p-cymene, camphene, citral, 2,3-dihydrobenzofuran, polylysine, and thiamine dilaurylsulfate at 1% was estimated at 1 to 2 log CFU/ml. The average hydrophilelipophile balance value of surfactants with sporicidal activity causing a reduction of 1 to 2 log CFU/ml was 9.3, with a range from 6.7 to 15.8, which is similar to the values of various chemical surfactants of 9.6 to 16.7. The results also showed that the surfactants that were hydrophobic were more effective than those that were hydrophilic in killing B. subtilis spores. Furthermore, the sporicidal effect of surfactants like geranyl acetate and γ-terpinene was significantly enhanced in the presence of a germinant, because L-alanine and synergistic cofactors (e.g., K(+) ions) trigger cortex hydrolysis in spores.