Title Page
Contents
ABSTRACT 15
Ⅰ. INTRODUCTION 18
Ⅱ. LITERATURE REVIEW 20
1. Chili pepper (Capsicum annuum L.) 20
2. Bacillus cereus 21
2.1. General characteristics 21
2.2. Toxins 22
2.3. Prevalence of B. cereus in food 25
3. Quantitative microbial risk assessment 27
3.1. Procedure and purpose 27
3.2. Trend of microbial risk assessment for B. cereus 28
Ⅲ. MATERIALS AND METHODS 30
1. Selection of agricultural products 30
2. Microbiological contamination levels in farms 30
2.1. Sample collection 30
2.2. Microbiological analysis 31
3. Characterization of B. cereus isolates 34
3.1. Preparation of B. cereus strains 34
3.2. Identification of hemolytic property 37
3.3. Antimicrobial susceptibility testing 37
4. Reduction of B. cereus in pepper by washing treatment 39
4.1. Sample preparation 39
4.2. Inoculation 39
4.3. Washing treatment 40
4.4. Statistical analysis 41
5. Development of predictive model for pepper 41
5.1. Growth pattern of B. cereus on storage temperature 41
5.2. Primary model 42
5.3. Secondary model 43
5.4. Model validation 43
6. Microbial risk assessment of B. cereus for pepper 44
6.1. Exposure scenario preparation 44
6.2. Risk characterization 46
Ⅳ. RESULT AND DISCUSSION 48
1. Selection of agricultural products 48
2. Microbial contamination level in farms 53
2.1. Quantitative microbiological analysis 53
3. Characterization of B. cereus isolates 62
3.1. Toxin genes 62
3.2. Hemolytic property 63
3.3. Antimicrobial susceptibility 68
4. Reduction of B. cereus in pepper by washing treatment 68
4.1 Removal effect of B. cereus 68
5. Development of predictive model for pepper 71
5.1. Growth pattern of B. cereus on storage temperature 71
5.2. Primary model 73
5.3. Secondary model 73
5.4. Model validation 78
6. Microbial risk assessment of B. cereus for pepper 80
6.1. Risk assessment simulation model 80
6.2. Risk characterization 105
Ⅴ. SUMMARY AND CONCLUSION 115
Ⅵ. REFERENCE 118
ABSTRACT IN KOREAN 126
Table 1. Classification of the two types of toxins caused by Bacillus cereus 24
Table 2. Prevalence of Bacillus cereus in Korea 26
Table 3. Primers for detection of Bacillus cereus 35
Table 4. Polymer chain reaction cycle for detection of gyrB and cry gene 36
Table 5. Antimicrobial resistance criteria of Bacillus cereus for disc diffusion antibiotic susceptibility assay 38
Table 6. Classification of vegetable 49
Table 7. Top 5 raw vegetables in most commonly consumed foods 50
Table 8. Prevalence of foodborne pathogens in vegetables 51
Table 9. Foodborne outbreaks associated with raw vegetables 52
Table 10. Number of total aerobic bacteria from environment samples collected from 6 farms 55
Table 11. Number of coliforms from environment samples collected from 6 farms 57
Table 12. Number of Staphylococcus aureus and Salmonella from environment samples collected from 6 farms 59
Table 13. Number of Bacillus cereus from environment samples collected from 6 farms 61
Table 14. List of isolated Bacillus cereus strains 64
Table 15. Polymer chain reaction result for Bacillus cereus isolates 65
Table 16. Hemolytic property of Bacillus cereus isolates 67
Table 17. Diameter of a clear zone formed by Bacillus cereus isolates 69
Table 18. Reduction of Bacillus cereus on green pepper after washing 70
Table 19. Parameters calculated by primary model for Bacillus cereus growth in green pepper 75
Table 20. Secondary models for μmax values and LPD values 76
Table 21. Validation of the predictive model in green pepper 79
Table 22. Excel spreadsheet for calculating the risk of Bacillus cereus in green pepper with @RISK 81
Figure 1. Step of microbiological risk assessment. 29
Figure 2. Flow chart for microbial risk assessment for green pepper. 47
Figure 3. Polymerase chain reaction results for Bacillus cereus isolates using primers targeting genes. 66
Figure 4. Populations of Bacillus cereus in green pepper during storage at 7℃, 15℃, 25℃, and 37℃. 72
Figure 5. Primary model for Bacillus cereus in green pepper during storage at 7℃, 15℃, 25℃, and 37℃. 74
Figure 6. Secondary models for kinetic parameters (μmax and LPD) as a function of storage temperature for green pepper.[이미지참조] 77
Figure 7. Probabilistic distribution for intake of green pepper obtained from the Korea national health and nutrition examination... 104
Figure 8. Probabilistic density of simulated initial contamination level of Bacillus cereus in pre-harvest green pepper. 106
Figure 9. Changes of Bacillus cereus contamination predicted level by distributions in green pepper during cultivation. 107
Figure 10. Changes of Bacillus cereus contamination level predicted by distributions up to washing. 110
Figure 11. Probability density of simulated final contamination level of Bacillus cereus in green pepper. 112
Figure 12. Correlation coefficient values for risk factors in green pepper production stage. 114