Inactivation of Cronobacter sakazakii an Salmonella enterica serovar Typhimurium by caprylic acid in combination with citric acid or vanillin in reconstituted infant formula
카프릴산과 구연산, 바닐린의 조합에 의한 조제분유 내 Cronobacter sakazakii와 Salmonella enterica serovar Typhimurium의 저감화
- 주제(키워드) infant formula , caprylic acid , citric acid , vanillin , Cronobacter sakazakii , Salmonella Typhimurium , flow cytometry , transmission electron microscopy
- 발행기관 고려대학교 대학원
- 지도교수 이민석
- 발행년도 2011
- 학위수여년월 2011. 2
- 학위구분 석사
- 학과 일반대학원 생명공학과
- 세부전공 식품공학전공
- 원문페이지 126 p
- 실제URI http://www.dcollection.net/handler/korea/000000025202
- 본문언어 영어
- 제출원본 000045641630
초록/요약
In this study, the antimicrobial effect of nature-derived compounds (caprylic acid, citric acid and vanillin) on the inactivation of Cronobacter sakazakii and Salmonella enterica (serovar Typhimurium) was examined in reconstituted infant formula. The formula samples were inoculated with three strains mixture of both bacteria yielding approximately 107 CFU/ml, and caprylic acid (10 and 20 mM), citric acid and vanillin (15 and 30 mM) were added periodically (0, 5, 10 and 30 min) at 40 and 45°C. At 40°C, the bacterial population was rarely reduced in the presence of 10 mM caprylic acid when used in combination with 15 mM citric acid or vanillin. Except for the above conditions, C. sakazakii and S. Typhimrium were significantly decreased (p < 0.05) as a function of time and significant synergistic effects were observed. C. sakazakii and S. Typhimurium were completely inactivated when treated with a combination of 20 mM caprylic acid and 30 mM citric acid or vanillin within 10 and 5 min, respectively. As the temperature was increased, the bactericidal effect was stronger at all time points and most combination treatments resulted in a synergistic effect. No recovery of injured desiccation stressed cells was observed in the formula samples that were inoculated at a low concentration (approximately 103 CFU/ml) in the validation analysis. Disintegration of the membrane integrity was determined by flow cytometry. In addition, changes in the cell morphology such as plasmolysis and membrane disruption were observed indicating that these combined treatments resulted in irreversible inactivation of the cells. The methods described in this study provide a new practical technique to eliminate contaminated bacteria in infant formula reconstitution. In addition, the definitive damaged observed in the cell could be helpful in better understanding the bactericidal mechanism of natural compounds in infant formula.
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ABSTRACT i
TABLE OF CONTENTS ii
LIST OF TABLES vi
LIST OF FIGURES viii
I. INTRODUCTION
1
II. REVIEW OF LITERAURE 4
2.1 Microbial exposure potentiality of infant formula 4
2.1.1 Microorganisms of concern in powdered infant formula 4
2.1.2 Microbial transmission route on infant formula 7
2.1.3 Cronobacter spp. and Salmonella spp. infection associated
with infant formula 10
2.2 Microbial characteristics of Cronobacter sakazakii and
Salmonella enterica serovar Typhimurium 16
2.2.1 Taxonomy and biochemical characterization 16
2.2.2 Contamination sources 22
2.2.3 Characteristics of the diseases 26
2.3 Inactivation studies of Cronobacter sakazakii and Salmonella
enterica serovar Typhimurium in infant formula 31
2.3.1 Physical treatments 31
2.3.1.1 Heat treatment 31
2.3.1.2 Pulsed electric field 31
2.3.1.3 Ionizing radiation 32
2.3.2 Chemical treatments 34
2.3.2.1 Medium chain fatty acid and theirs monoglycerides 34
2.4 Natural antimicrobials activity: Caprylic acid, citric acid,
and vanillin 36
2.4.1 Caprylic acid 36
2.4.1.1 Description of caprylic acid 36
2.4.1.2 Antimicrobial action of caprylic acid 37
2.4.1.3 Application studies of caprylic acid in foods 39
2.4.2 Citric acid 40
2.4.2.1 Description of citric acid 40
2.4.2.2 Antimicrobial action of citric acid 40
2.4.2.3 Application studies of citric acid in foods 41
2.4.3. Vanillin 42
2.4.3.1. Description of vanillin 42
2.4.3.2. Antimicrobial action of vanillin 42
2.4.3.3. Application studies of vanillin on foods 43
III. MATERIALS AND METHODS
45
3.1 Preparation of culture 45
3.2 Sample preparation and inoculation 46
3.3 Preparation of antimicrobials 46
3.4 Antimicrobial activity assays 47
3.4.1 Single treatment 47
3.4.2 Double combined treatment 47
3.5 Validation of combined treatment 48
3.5.1 Desiccation stressed cells 48
3.5.2 Determination of injured cells 48
3.6 Flow cytometric analysis 49
3.6.1 Fluorescent staining 49
3.6.2 Flow cytometric measurement 50
3.7 Transmission electron microscopy 51
3.8 Statistical analysis 52
IV. RESULTS AND DISCUSSION 53
4.1 Determination of antimicrobial activity for individual
compounds 53
4.1.1 Caprylic acid 53
4.1.2 Citric acid 55
4.1.3 Vanillin 56
4.2 Combined effect of caprylic acid with citric acid or vanillin 62
4.2.1 Combination of caprylic acid and citric acid 62
4.2.2 Combination of caprylic acid and vanillin 70
4.3 Validation assays of antimicrobial effects on desiccation
stressed cells 76
4.4 Disintegration of membrane surface 81
4.4.1 Flow cytometric analysis 81
4.4.2 Transmission electron microscope analysis 85
V. CONCLUSION 89
ABSTRACT IN KOREAN 91
REFERENCES 92
