Antimicrobial activities of combined treatments of gaseous chlorine dioxide and heat at high relative humidity against Xanthomonas campestris and Salmonella enterica on cabbage, chili pepper, and radish seeds

다국어 초록 (Multilingual Abstract)

The aim of this study was to develop a method to inactivate Xanthomonas campestris and Salmonella enterica on cabbage, chili pepper, and radish seeds using combination of gaseous chlorine dioxide (ClO2) and heat at high relative humidity (RH) in a short time without decreasing the viability of seeds. Gaseous ClO2 was vaporized from the mixed solution of hydrochloric acid (HCl, 1 N) and sodium chlorite (NaClO2, 100,000 ppm) (HCl-NaClO2 solution). To produce gaseous ClO2 in high concentration (up to 3,000 ppm) in a 1.8 L sealed container at 70°C and 85% RH, a standard curve which showed the relationship between the amount of HCl-NaClO2 solution and the concentration of gaseous ClO2 was constructed (y = 5758.3x; R2 = 0.9981). Next, the influence of combined treatment of gaseous ClO2 (up to 3,000 ppm) and heat (70°C and 85% RH) on the germination of seeds were determined. As a result, it was confirmed that the germination rates of cabbage, chili pepper, and radish seeds did not significantly decrease (P > 0.05) for 30, 20, and 60 min, respectively, after the treatment. Finally, the antimicrobial activities of combined treatments against X. campestris and S. enterica on cabbage, chili pepper, and radish seeds were determined. After the combined treatment for 20 min, X. campestris cells (ca. 6.2-6.4 log CFU/g) were inactivated and the populations of S. enterica (ca. 6.3-6.5 log CFU/g) were decreased to < 1.2 log CFU/g, regardless of types of seeds. This study provides useful information for the development of decontamination methods of vegetables seeds to inactivate plant or foodborne pathogens using combined treatment with gaseous ClO2 and heat at high RH.

국문 초록 (Abstract)

본 연구의 목적은 이산화염소 기체와 습열의 조합처리로 짧은 시간안에 양배추, 고추, 그리고 무 종자에 접종된 Xanthomonas campestris와 Salmonella enterica를 종자의 발아율에 영향없이 멸균하는 방법을 개발하는 것이다. ¬이산화염소 기체는 염산(HCl, 1N)과 아염소산나트륨 (NaClO2, 100,000 ppm)의 혼합액으로부터 자연기화해 만들어졌다. 먼저, 70°C의 온도와 85% 상대습도로 조절된 1.8 L container에서 고농도의 이산화염소 기체(3,000 ppm)를 생산하기 위해 HCl-NaClO2 혼합액의 양과 그로부터 발생한 이산화염소 기체 농도의 관계식을 도출하였다(y = 5758.3x; R2 = 0.9981). 다음으로, 이산화염소 기체(3,000 ppm)와 습열(70°C 및 85% RH)의 조합처리가 종자의 발아에 미치는 영향을 확인했다. 양배추, 고추, 그리고 무 종자의 발아율은 각각 30, 20, 그리고 60 분의 조합처리에도 유의적으로 감소하지 않았음을 확인하였다(P > 0.05). 마지막으로 양배추, 고추, 그리고 무 종자에 접종된 X. campestris와 S. enterica에 대한 조합처리의 살균력을 측정하였다. 조합처리 20분 후, 종자에 접종된 X. campestris (ca. 6.2-6.4 log CFU/g)와 S. enterica (ca. 6.3-6.5 log CFU/g)의 개체수는 종자의 종류와 상관없이 각각 완전히 멸균되거나 1.2 log CFU/g 이하로 감소하였다. 본 연구는 이산화염소 기체 와 습열의 조합처리로 채소 종자의 오염된 식물 또는 식중독 병원균을 제거 방법 개발에 유용한 정보를 제공할 것이다.

목차 (Table of Contents)

• Ⅰ. Introduction 1
• Ⅱ. Literature review 4
• 2.1. Xanthomonas campestris 4
• 2.2. Salmonella enterica 5
• 2.3. Chlorine dioxide 6
• Ⅲ. Materials and methods 8
• 3.1. Construction of a sealed containers 8
• 3.2. Production of gaseous ClO2 10
• 3.3. Influence of combined treatment of gaseous ClO2 and heat at high RH on the germination rates of seeds 10
• 3.3.1. Treatment of seeds with gaseous ClO2 and heat at high RH 10
• 3.3.2. Determination of seed germination rate 11
• 3.4. Antimicrobial activities of combined treatment of gaseous ClO2 and heat at high RH against X. campestris or S. enterica on seeds 12
• 3.4.1. Preparation of inoculum 12
• 3.4.2. Inoculation of X. campestris or S. enterica on seeds 13
• 3.4.3. Treatment of inoculated seeds with gaseous ClO2 and heat at high RH 13
• 3.5. Observation of seed surfaces and S. enterica inoculated on seeds by field emission scanning electron microscopy 14
• 3.6. Statistical analysis 15
• Ⅳ. Result 16
• 4.1. Production of gaseous ClO2 16
• 4.2. Influence of combined treatment of gaseous ClO2 and heat at high RH on the germination rates of seeds 19
• 4.3. Antimicrobial activities of combined treatment of gaseous ClO2 and heat at high RH against X. campestris or S. enterica on seeds 19
• 4.4. Observation of seed surfaces and S. enterica inoculated on seeds by FE-SEM 25
• Ⅴ. Discussion 28
• Reference 34
• Acknowledgement 46