• Food Science and Preservation
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• v.21 no.4
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• pp.468-472
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• 2014

The effect of pre-storage treatments was investigated to control the occurrence of fruit skin stain in 'Niitaka' pears. The incidence of fruit skin stains was significantly reduced when the fruits were stored in paper bags with a yellow inner color, compared to when they were stored in paper bags with blue and red inner colors. Additionally, the pear fruits that were harvested seven days earlier than their optimum maturity date developed less fruit skin stains in cold storage and retained their quality. Storage in polyethylene (PE) bags did not control the occurrence of fruit skin stains as effectively as did bag-free storage or storage in calcium-coated bags. The dipping of the pear fruits in a chlorine dioxide and calcium solution was highly effective in reducing the fruit skin stains compared to when they were not dipped or when they were dipped only in distilled water. In particular, a 1,500 times diluted solution of sodium dichloroisocyannurate (NaDCC) reduced the incidence of fruit skin stains and the size of the lesions. No stain was observed on the skin of the fruit with a water content lower than 67.7% (w/v) during its storage. In conclusion, packaging pear fruits in bags with an inner calcium coat and dipping them in a chlorine dioxide, calcium, or NaDCC solution can effectively reduce their skin stains during their storage.

• Journal of Environmental Impact Assessment
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• v.29 no.6
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• pp.403-413
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• 2020

A mathematical model comprised with eight simultaneous quasi-linear partial differential equations was suggested to provide optimal chlorination strategy. Upstream weighted finite element method was employed to construct multidimensional numerical code. The code was verified against measured concentrations in three type of reactors. Boundary conditions and reaction rate were calibrated for the sixteen cases of experimental results to regenerate the measured values. Eight reaction rate coefficients were estimated from the modeling result. The reaction rate coefficients were expressed in terms of pH and temperature. Automatic optimal algorithm was invented to estimate the reaction rate coefficients by minimizing the sum of squares of the numerical errors and combined with the model. In order to minimize the concentration of chlorine and pollutants at the final usage sites, a real-time predictive control system is imperative which can predict the water quality variables from the chlorine disinfection process at the water purification plant to the customer by means of a model and operate the disinfection process according to the influent water quality. This model can be used to build such a system in water treatment plants.

• Journal of Food Hygiene and Safety
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• v.38 no.5
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• pp.287-296
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• 2023

Mushroom consumption is gradually growing annually worldwide for many centuries. Oyster mushrooms (Pleurotus ostreatus), button mushrooms (Agaricus bisporus), and enokitake (Flammulina filiformis) are mainly consumed in Korea. However, mushrooms can be contaminated with pathogenic microorganisms, such as Listeria monocytogenes, because antibacterial treatment during mushroom cultivation and processing is insufficient. Therefore, many cases of mushroom contamination-related foodborne illnesses and food recalls have been reported. Three representative treatments are used to prevent microbial contamination in mushrooms: chemical, physical, and combination treatments. Among the chemical treatments, chlorine compounds, peroxyacetic acid, and quaternary ammonium compounds are commercially used and ozone and electrolyzed water has recently been used. Additionally, physical treatments, including ultrasound, irradiation, and cold plasma, are being developed. Combination techniques include ultraviolet/chlorine compounds, ozone/organic acid, and ultrasound/organic acid. This review describes the domestically consumed mushroom types and their characteristics, and investigates the mushroom contamination levels. Additionally, effective antibacterial technologies for reducing microbial contamination in mushrooms are also discussed.

• Journal of Food Hygiene and Safety
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• v.26 no.4
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• pp.417-423
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• 2011

Salted Cabbage products purchased from different companies at 4 different districts in South Korea were detected in this study. Cabbage and salt are the main materials for kimchi manufacture. The results of general bacteria contaminated in the samples were $1.4{\times}10^5$, $6.4{\times}10^5$, $1.7{\times}10^7$, $3.6{\times}10^7$ CFU/g in cabbage and $2.7{\times}10^3$ CFU/g in salt, respectively. The results of coliforms were detected as $2.4{\times}10^4$ CFU/g, and there was no Escherichia coli in any sample. Staphylococcus aureus was detected in cabbage as $9.9{\times}10^2$, $8.0{\times}10^1$, and $3.0{\times}10^3$ CFU/g, Bacillus cereus was also found in cabbage as $4.1{\times}10^3$ and $1.0{\times}10^1$ CFU/g. The results of Campylobacter jejuni and Vibrio paraheamolyticus were $2.4{\times}10^6$ and $1.0{\times}10^4$ CFU/g in cabbage, respectively. $1.0{\times}10^3$ CFU/g for Yersinia enterocolitica was determined in salt. In case of Listeria monocytogenes, the results were $1.5{\times}10^1$, $1.1{\times}10^2$, and $4.5{\times}10^1$ CFU/g in cabbage. Total batcteria ranged from $1.4{\times}10^1$ to $4.4{\times}10^5$ CFU/g were detected in salting solution, from $1.5{\times}10^4$ to $1.2{\times}10^8$ CFU/g in dehydrated salted-cabbage, from $9.4{\times}10^4{\sim}1.3{\times}10^8$ CFU/g in minced salted-cabbage. The results of E. coli in samples from different companies were different from one to anther. The results of the contamination of S. aureus and B. cereus showed positive in salting solution and dehydrated salted-cabbage at a portion of companies. V. paraheamolyticus was detected in salting solution. The contamination of Y. enterocolitica ranged from $9.5{\times}10^2$ to $1.8{\times}10^3$ CFU/g in salting solution, from $1.7{\times}10^1$ to $2.7{\times}10^2$ CFU/g in dehydrated salted-cabbage, from $1.2{\times}10^2$ to $1.3{\times}10^8$ CFU/g in minced salted-cabbage. The contamination of L. monocytogenes ranged from $8.0{\times}10^2$ to $1.7{\times}10^4$ CFU/g in salting solution, from $2.8{\times}10^2$ to $1.2{\times}10^4$ CFU/g in dehydrated salted-cabbage. During the manufacture processing of Kim chi, microorganisms were detected in cabbages salted in different concentrations of salt solution at 8%, 10%, 12% and 15% for 5-20 hours. As the results, $3.5{\times}10^5-1.7{\times}10^6$, $3.4{\times}10^5-2.5{\times}10^6$, $5.4{\times}10^5-2.3{\times}10^6$, $4.0{\times}10^5-2.3{\times}10^6$ CFU/g were detected for E. coli in samples at different treatment conditions. $1.9{\times}10^4-4.1{\times}10^4$, $4.1{\times}10^3-2.8{\times}10^4$, $1.5{\times}10^3-7.8{\times}10^3$, $2.2{\times}10^4-6.6{\times}10^4$ CFU/g were detected for S. aureus in samples at different treatment conditions. Salmonella typhimurium was detected in salted cabbage with various salt concentration after salting for 5 hrs, the result ranged from $2.5{\times}10^5$ to $3.8{\times}10^6$ CFU/g, and change of microorganism was the smallest in salted cabbage under the concentration of salting solution at 10% for 15 hours. The cabbage salted in 10% salting solution for 15 hours were washed with water for 2 and 3 times, with chlorine for 3 times, and with acetic acid for 3 times. E. coli was detected in the samples washed with water for 2 and 3 times, washed with chlorine for 3 times. The contamination of S. aureus was $3.0{\times}10^5$ CFU/g in the samples washed with water for 2 times, $5.6{\times}10^3$ CFU/g in the samples washed with acetic acid for 3 times, $3.6{\times}10^5$ CFU/g in the samples washed with water for 3 times and same amount in the samples washed with chlorine for 3 times. According to the results, the contamination of S. aureus was $5.6{\times}10^3$ CFU/g lower in samples washed with chlorine and acetic acid than that in samples washed with water. In case of S. typhimurium, it has been detected in samples washed with water and chlorine, $3.0{\times}10^1$ CFU/g as the lowest concentration among all the samples was measured in the samples washed with acetic acid for 3 times.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.5
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• pp.359-367
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• 2011

The Process of Pressurized water diffusion is mixing process by pressurized water injection with coagulate and chlorine water in the water treatment system. The objectives of this research were to evaluate the mixing length and diameter of diffusion plate and distance from injection pipe for complete mixing by using computational fluid dynamics. From the results of CFD simulation, when diameter of injection pipe is 50 mm, 100 mm and injection pressure is $5kg/cm^2$ and the diameter of inlet pipe is 2,200 mm, the complete mixing length is 4D (D: Length as diameter of inlet pipe). When diameter of injection pipe is 50 mm, the diameter of the diffusion plate in o.1D and distance from injection pipe is 0.2D, the complete mixing length is 3D that is the most short mixing length. But when diameter of injection pipe is 100 mm and mutually related the diameter, distance of diffusion plate, the complete mixing length is 4D over. Therefore, as the diameter of inlet pipe is 2,200 mm, the injection pipe 50 mm is more efficient than 100 mm.

• Journal of Korean Society on Water Environment
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• v.24 no.1
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• pp.123-128
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• 2008

The Dissolved Organic Carbon (DOC) existing in a water includes both hydrophobic and hydrophilic substances however, most of the discussion focuses on hydrophobic substances. The hydrophobic fraction was easily removed by absorption or coagulation more than hydrophilic fraction. Therefore, control of the hydrophilic fraction is very important in water treatment process. This study is to determine the variation of DOC, the removal efficiency of DOC, and Trihalomethane formation potential (THMFP) after each stage of water treatment process by fractionating Natural Organic Matters (NOM) into hydrophobic and hydrophilic substance. DOC from raw water was fractionated at acidic pH (pH<2) using XAD 8 resin column, into two fraction : hydrophobic substance (i.e. humic substance) adsorbed on XAD 8 and hydrophilic substance which represent the organics contained in the final effluent. THMFP was carried out according to the following set condition: Cl2/DOC=4 mg/mg, incubation at $25^{\circ}C$ in darkness, pH 7 adjust with HCl or NaOH as necessary, and 72hour-contact time. THMs analyzed in this study were chloroform, bromodichloromethane, dibromochloromethan, and bromoform. Sewage was almost evenly split between the hydrophobic (56%) and hydrophilic fraction (44%). But, Aldrich humic substance (AHS) was found to contain less hydrophilics (14%) than hydrophobics (86%). The formation of THMs may depend on the source which is characterized by the composition of organic matters such as AHS and sewage. The THMFP yield of sewage and AHS were assessed as follows. The value of the THMFP reaction yield, AHS $172.65{\mu}g/mg$, is much higher than that of sewage $41.68{\mu}g/mg$. This illustrates possible significant difference in THMFP according to the component type and the proportion of organic matter existing in water source. Apparently AHS react with chlorine to produce more THMFP than do the smaller molecules found in sewage. Water treatment process may reduce THMFP, nevertheless residual DOC (the more hydrophilic substance) has significant THMFP. Further reduction in organic halide precursors requires application of alternative treatment techniques.

• Korean Journal of Microbiology
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• v.51 no.4
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• pp.355-363
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• 2015

The present work quantified the growth of young biofilm in a model distribution system that was fed with chlorinated drinking water at a hydraulic retention time of 2 h. Bacterial biofilms grew on the surface of polyvinyl chloride (PVC) slides at a specific growth rate of $0.14{\pm}0.09day^{-1}$ for total bacteria and $0.16{\pm}0.08day^{-1}$ for heterotrophic bacteria, reaching $3.1{\times}10^4cells/cm^2$ and $6.6{\times}10^3CFU/cm^2$ after 10 days, respectively. The specific growth rates of biofilm-forming bacteria were found to be much higher than those of bulk-phase bacteria, suggesting that biofilm bacteria account for a major part of the bacterial production in this model system. Biofilm isolates exhibited characteristic kinetic properties, as determined by ${\mu}_{max}$ and $K_S$ values using the Monod model, in a defined growth medium containing various amounts of acetate. The lowest ${\mu}_{max}$ value was observed in bacterial species belonging to the genus Methylobacterium, and their slow growth seemed to confer high resistance to chlorine treatment (0.5 mg/L for 10 min). $K_S$ values (inversely related to substrate affinity) of Sphingomonas were two orders of magnitude lower for acetate carbon than those of other isolates. The Sphingomonas isolates may have obligate-oligotrophic characteristics, since the lower $K_S$ values allow them to thrive under nutrient-deficient conditions. These results provide a better understanding and control of multi-species bacterial biofilms that develop within days in a drinking water distribution system.

• Journal of agricultural medicine and community health
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• v.9 no.1
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• pp.56-66
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• 1984

Giardia lamblia is a pathogenic flagellate causing intestinal disorders such as diarrhea, abdominal pain and malabsorption of nutrients. Giardia is mainly infected by the ingestion of contaminated foods per os. Craun (1979) has recently reported that mass infection of this flagellate through the contaminated water supply systems is one of public health hazards. Also, so-called traveller's diarrhea is sometimes caused by Giardia infection (CDC, U.S.A., 1971). However, a few epidemiological studies figuring out the mode of infection or control measures of Giardia infection has been done so far in Korea. The present study was aimed to know the prevalence of Giardia infection in several Korean populations, detectability of this flagellate in water systems and the viability of the cysts against sewages and disinfectants applying to drinking water. In the present study, 388 stool specimens from orphanage children in Chun-joo, Chung-joo, On-yang and Chun-an areas and 538 stool specimens from inhabitants in Woo-do, In-chon, and Chun-joo were examined by formalin-ether concentration technique to detect out Giardia cysts. On the other hand, water samples from 14 sites of Han River and its tributaries were collected in May through July, 1984. Fifty liter of water sample in each sampling site was then filtered through water filtering system deviced by U.S. Environmental Proutection Agency and the sediments rinsed out from the thread rolls, a part of water filtering system, were examined to detect out the Giardia cysts. In order to observe the viability of Giardia cysts in the sewage samples, the cysts were treated in it at $4^{\circ}C$ or $25^{\circ}C$ for 7 through 28 days. For this purpose, the cysts were also exposed to various concentrations of disinfectants such as chlorine, iodine and ozone gas for proper time intervals. After treatment, the viability test of the Giardia cysts were carried out by method of Rice and Schaefer (1981) with minor modification. The results obtained in this study were as follows : 1) The detection rates of G lamblia cysts in the stool specimens were 18.3% in orphans and 4.3% in general examinees. 2) The prevalences of Giardia Infection were higher in the young age groups than in-adults. The highest positive rate was 18.4% in the age group less than 10. 3) Of 14 water specimens sampled from Han River system and its tributaries around the Seoul area, the Giardia cysts were detected from 4 samples, and no cyst was found in the water supply systems. 4) The cysts treated in the sewage survived for 28 days at $4^{\circ}C$ and for 13 days at $25^{\circ}C$. 5) The cysts were completely destroyed within 60 minutes by exposure to 8 mg/l of residual chlorine at 4g and within 30 minutes by exposure to the same concentration of chlorine at $25^{\circ}C$. 6) The cysts were all dead when exposed to 1 mg/1 of iodine for 60 minutes at $4^{\circ}C$ or $25^{\circ}C$. 7) The cysts were destroyed after 10 minute exposure in 0.15 mg to 0.25mg of residual ozone gas per liter. Summarizing the above results, it is considered that Giardia infection is regarded as water-borne disease and the cysts are able to be controlled by the application with the disinfectants in the water supply systems.

• 한국균학회소식:학술대회논문집
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• 2014.10a
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• pp.25-25
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• 2014

Three species of Fusarium, F. fujikuroi, F. verticillioides and F. proliferatum, are known to be associated with bakanae disease of rice [1, 2]. F. fujikuroi infects rice flowers and survive in endosperm and embryo of the seeds. Infected seed is an important source of primary inoculum of pathogens [3]. Seeds of rice (Oryza sativa cv. Boramchan) collected from bakanae-infected field were found to be 96% infected with Fusarium sp., 52% with F. fujikuroi, 42% with F. verticillioides, and 12% with F. proliferatum as determined by incubation method and species-specific PCR assays. F. fujikuroi was detected at lemma/palea, endosperm and embryo whereas F. verticillioides and F. proliferatum were recovered only from lemma/palea by means of component plating test. Seed disinfection methods have been developed to control bakanae disease and prochloraz has been most widely used for rice seeds. Two chemicals formulated with prochloraz (PC 1) and prochloraz + hexaconazole (PC 2) that inhibit biosynthesis of ergosterol strongly reduced the incidence of Fusarium spp. on selective media to 4.7% and 2.0%, respectively. Disease symptoms of rice seedlings in nursery soil were alleviated by chemical treatment; seedlings with elongated leaves or wide angle between leaf and stem were strikingly reduced from 15.6 to 3.2% (PC 1) and 0 (PC 2), stem rots were reduced from 56.9 to 26.2% (PC 1) and 32.1% (PC 2), and normal seedling increased from 0.4 to 13.3% (PC 2). Prochloraz has some disadvantages and risks such as the occurrence of tolerant pathogens [4] and effects on the sterol synthesis in animals and humans [5]. For these reasons, it is necessary to develop new disinfection method that do not induce fungal tolerance and are safe to humans and animals. Chlorine dioxide ($ClO_2$), that is less toxic, produces no harmful byproducts, and has high oxidizing power, has been reported to be effective at disinfection of several phytopathogenic fungi including Colletotrichum spp. and Alternaria spp. [6]. Gaseous $ClO_2$ applied to rice seeds at a concentration of 20 ppm strongly suppressed mycelial growth of Fusarium fujikuroi, F. verticillioides and F. proliferatum. The incidence of Fusarium spp. in dry seed with 8.7% seed moisture content (SMC) tended to decrease as the concentration of $ClO_2$ increased from 20 to 40 ppm. Applying 40 ppm $ClO_2$ at 90% relative humidity, incidence was reduced to 5.3% and resulted in significant reduction of disease symptoms on MS media. In nursery soil, stem rot was reduced from 56.9 to 15.4% and the number of normal seedlings increased from 0.4 to 25.5%. With water-soaked seeds (33.1% SMC) holding moisture in the endosperm and embryo, the effectiveness of disinfection using $ClO_2$ increased, even when treated with only 20 ppm for four hours. This suggests that moisture was a key element for action of $ClO_2$. Removal of the palea and lemma from seeds significantly decreased the incidence of Fusarium spp. to 3.0%. Seed germination appeared to decrease slightly by water-soaking at $30^{\circ}C$ because of increased SMC and by physical damage of embryos from hulling. These results indicate that the use of gaseous $ClO_2$ was effective as a means to disinfect rice seeds infected with Fusarium spp. and that moisture around the pathogens in the seed was an important factor for the action of $ClO_2$. Further investigations should be conducted to ascertain the best conditions for complete disinfection of Fusarium spp. that infect deep site of rice seeds.

• Journal of Food Hygiene and Safety
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• v.34 no.2
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• pp.170-177
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• 2019

The aim of this study was to investigate the effect of different concentrations of chlorine dioxide ($ClO_2$) on sterilization and deodorization of food-holding cabinets under different exposure times. For the measuring sterilization and deodorization, a 6.5 L chamber and a 625 L cabinet with circulation systems were used. Two bacteria (Staphylococcus aureus KCTC1916 and Escherichia coli KCTC 1682) that were artificially inoculated in the plate respectively were put into the 6.5 L chamber and the 625 L cabinet. The $ClO_2$ gas was produced by ampules. In the 6.5 L chamber, neither of the two bacteria was detected after 24 hours treatment by $ClO_2$ gas. Moreover, the deodorization rate against ammonia and phenol was 94% and 70%, respectively, but deodorization against formaldehyde was not effective. When the concentration reached maximum (6 ampule, 4.6 ppm) levels in the cabinet, it lasted for approximately 2 h and then decreased slowly. When a circulator was used, the gas concentration was very low (6 ampule, 0.8 ppm) and the antibacterial activity against S. aureus and E. coli was low. The level of reduction against S. aureus and E. coli was 2.98 log CFU/plate and 6.06 log CFU/plate, respectively, in the cabinet after 24 h without a circulator. The reduction against S. aureus KCTC1916 and E. coli KCTC1682 was 2.69 log CFU/plate and 4.41 log CFU/plate for 24 h, respectively.