This study investigated the effects of sodium chloride (NaCl) and various acids, alone or in combination, on Shigella flexneri growth in laboratory medium and cucumber puree.Shigella flexneri was treated with various acids (acetic, citric, malic, tartaric, propionic, lactic and phosphoric acid) alone or with 3, 6 or 9% NaCl. Pronounced antagonistic effects were observed in Sh. flexneri treated with acetic or lactic acid in combination with 3% NaCl. Next, Sh. flexneri was pre-exposed to 3% NaCl and then treated with various acids; acid-stressed cells were then inoculated onto agar plates containing 3% NaCl. There was no significant difference in the reduction of Sh. flexneri, regardless of treatment (P > 0·05). Finally, Sh. flexneri was inoculated into cucumber puree to which various concentrations of acetic acid had been added with and without 3% NaCl. Antagonistic effects were observed with a treatment of either 0·5 or 1% acetic acid combined with 3% NaCl.Antagonistic effects were observed when Sh. flexneri was exposed to acetic or lactic acid with NaCl.This study shows that depending on the type of acid, the addition of NaCl can increase the resistance of Sh. flexneri to acid treatments. This may provide useful information for developing methods of preserving acidified foods.
Abstract This study determined the antimicrobial activities of acetic acid, citric acid and lactic acid against four S higella species: S . sonnei , S . flexneri , S . boydii and S . dysenteriae . Minimal inhibitory concentrations of acetic acid and citric acid against S higella were 200 and 300 ppm, respectively. But S . sonnei was 400 ppm. Lactic acid (0.5%) in tryptic soya broth inhibited the growth of all S higella species. Citric acid weakly inhibited the growth of S . flexneri , but it strongly inhibited the growth of S . dysenteriae , resulting in a 5‐log reduction. Acetic acid exhibited the weakest antimicrobial activity among the tested organic acids but produced the highest ratios of injured cells. When artificially inoculated lettuce was dipped in 1% organic acid solutions, the growth of S . flexneri, S . dysenteriae and S . boydii were reduced by 2 logs. And the growth was further reduced by lactic acid as the dipping time increased. The antimicrobial activities of organic acids against S higella species differed. Acetic acid exhibited the greatest antimicrobial activity in the paper disk diffusion experiment, but lactic acid was the most effective antimicrobial agent against S higella species artificially inoculated on lettuce. Practical Applications Shigellosis induced by S higella species results in at least 600,000 deaths worldwide each year. And in the U.S.A. , it is a major bacteria involved in food poisoning, reported in 10,000–20,000 patients. In the present study, organic acids were used as basic materials for controlling S higella species, and there are potential for organic acids, which are natural antimicrobials, to be used in the development of eco‐friendly reduction technology on S higella species.
본 연구에서는 시멘트의 유해성을 극복하기 위하여 시멘트 대신에 친환경 토양안정재를 사용한 식생블록을 제작하여 압축강도 및 휨강도 특성을 규명하였다. 식생블록 제작에 사용된 토양안정재는 천연섬유에서 추출한 단섬유와 석회 등을 주원료로 하며 흙의 전단강도를 증가시켜 블록의 내구성을 향상시키면서 식생을 가능하게 하는 특징을 가지고 있다. 일축압축강도 시험을 위한 공시체는 토양안정재와 화강풍화토를 혼합하여 제작하였으며, 토양안정재는 혼합토의 중량대비 6 %, 12 %, 18 %로 변화시켜 물과 교반하였다. 공시체는 공기 중에서 건조하여 각각 5일, 7일, 14일, 28일간 양생시키고 일축압축강도 시험을 수행하였다. 휨강도 시험은 일축압축강도 시험과 동일한 조건으로 블록을 제작하여 각 단계별 휨강도 시험을 실시하였고 현장 적용성 평가를 위하여 토양안정재의 특성을 고려한 최적함수비를 제안하였다. 또한 식생블록에 대한 투수시험 결과 KS F 4419에서 규정하는 투수성 블록의 품질기준을 만족하는 것으로 나타났다. With a view to resolving environmental problems of hazardous cement, this study seeks to identify the unconfined compressive strength and bending strength of the vegetation block designed herein by utilizing high-strength natural soil stabilizer instead of cement. Soil stabilizer is mainly made of mixture of short fiber extracted from natural fiber and lime, etc. Soil stabilizer reinforces the shearing strength of soil to improve block supportive power and durability while preventing flood and frost damages. For the unconfined compressive strength test, test pieces were prepared by mixing soil stabilizer and weathered soil in different ratios of 6 %, 12 % and 18 %. Experiments were carried out according to curing periods of 5th, 7th, 14th and 28th of the day. For bending strength test, blocks were made in the same mixture ratios as for the unconfined compressive test and tested for each stage. Also, to evaluate for the field applicability, proposed optimum water content considering the characteristics of the soil stabilizer. Permeability test result for the vegetation block, satisfied by the KS F 4419 quality standards.
Pectobacterium carotovorum subsp. carotovorum and Dickeya chrysanthemi have been reported to cause soft-rot diseases to fresh produces. The aim of this research was to investigate the inactivation efficacy of a 222 nm KrCl excimer lamp and 280 nm UVC-LED against P. carotovorum subsp. carotovorum and D. chrysanthemi on fresh produces. When samples were subjected to UVC treatment by a excimer lamp or UVC-LED at 450 mJ/cm2, it was observed that soft-rot bacteria on the surface of iceberg lettuce, strawberry, and tomato were reduced by a maximum of 5, 3, and 5 log units, respectively. The surface properties of fresh products, such as hydrophobicity, roughness, and topographic image, were analyzed under the hypothesis that the characteristics of the sample surface affected the inactivation efficacy of the excimer lamp and UVC-LED. It was determined that there was an inverse correlation between the surface roughness and inactivation efficacy of UVC treatment. The texture properties of samples were not significantly different (P > 0.05) from those of untreated samples. The results of this research substantiate that the excimer lamp and UVC-LED can be applied to decontamination processes for inactivating soft-rot bacteria, thereby prolonging the shelf life of fresh produce and reducing economic losses.
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