Bactericidal action of syringic acid and mild heat involving stress response in foodborne pathogens = 시링산과 미열 처리에 의한 병원성 미생물 살균 작용 및 스트레스 반응 기반 메커니즘 분석

다국어 초록 (Multilingual Abstract)

Hurdle technology, which integrates multiple preservation methods, is gaining attention as a means to enhance microbiological food safety. This study investigated the synergistic antimicrobial effect of syringic acid (SA) and mild heat (MH) against four major foodborne pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus) in buffer and tomato juice. Treatments were performed using SA (5 mM), MH (50°C), or their combination for up to 20 min. The combined treatment resulted in at least a 5-log reduction in all tested pathogens, showing clear synergistic bactericidal activity compared with individual treatments. Mechanistic analyses revealed that the combined treatment caused greater membrane permeability and loss of metabolic activity, as evidenced by increased propidium iodide uptake, decreased iodonitrotetrazolium chloride reduction, and reduced activities of glycolytic enzymes (hexokinase, phosphofructokinase, and pyruvate kinase). Importantly, the treatment did not significantly affect key quality parameters of tomato juice, including color and lycopene content. These findings demonstrate that the combination of SA and MH effectively inactivates diverse foodborne pathogens through multi-targeted cellular damage while preserving product quality, suggesting its potential as a practical and natural approach to improve food safety in liquid food matrices.

국문 초록 (Abstract)

허들기술은 다양한 보존 기법을 통합하여 식품의 미생물학적 안전성을 향상시키는 방법으로 주목받고 있다. 본 연구는 시링산(syringic acid, SA)과 미열(mild heat, MH) 처리의 병용이 네 가지 주요 식중독균(Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, Listeria monocytogenes, Staphylococcus aureus)에 대해 나타내는 상승적 항균효과를 완충용액과 토마토 주스에서 평가하였다. 실험은 syringic acid(5 mM), mild heat(50°C), 또는 이들의 병용 처리를 최대 20분까지 적용하여 수행하였다. 그 결과, 병용 처리는 모든 시험 균주에서 최소 5-log 이상의 감소를 유도하여 단일 처리 대비 명확한 상승적 살균효과를 나타냈다. 작용 기전 분석 결과, 병용 처리는 propidium iodide(Pi) 흡수 증가, iodonitrotetrazolium chloride(INT) 환원 감소, 그리고 해당작용 관련 효소(hexokinase, phosphofructokinase, pyruvate kinase)의 활성 저하로 확인된 바와 같이 세포막 투과성 증가와 대사활성 손실을 더욱 심화시키는 것으로 나타났다. 또한, 토마토 주스의 색도 및 라이코펜 함량을 포함한 주요 품질 지표는 유의적인 변화가 관찰되지 않았다. 본 연구 결과는 SA와 MH의 병용이 다중 표적의 세포 손상을 통해 다양한 식중독균을 효과적으로 불활성화하면서도 제품 품질을 유지할 수 있음을 보여주며, 액상 식품 매트릭스에서 활용 가능한 천연 기반 식품 안전성 향상 기술로서의 잠재력을 시사한다.

목차 (Table of Contents)

• ABSTRACT I
• CONTENTS III
• LIST OF TABLES V
• LIST OF FIGURES VI
• Ⅰ. INTRODUCTION 8
• Ⅱ. MATERIALS AND METHODS 11
• 2.1. Bacterial strains and cell suspension 11
• 2.2. Sample preparation and inoculation 11
• 2.3. Preliminary test for treatment condition selection 12
• 2.4. Bactericidal treatments 13
• 2.5. Bacterial enumeration 14
• 2.6. Pathogen inactivation curve fitting 15
• 2.7. Bactericidal mechanism 15
• 2.7.1. Assessment of cell membrane damage using propidium iodide uptake 15
• 2.7.2. Respiratory enzyme activity assay using INT reduction 16
• 2.7.3. Enzyme activity analysis in the Embden-Meyerhof-Parnas (EMP) pathway 17
• 2.8. Color and Lycopene measurement 17
• 2.9. Statistical analysis 19
• Ⅲ. RESULTS 20
• 3.1. Preliminary tests for treatment condition optimization 20
• 3.2. Bactericidal effect of syringic acid, mild heat, and combination treatment in BPW 24
• 3.3. Bactericidal mechanism of combination treatment of syringic acid and mild heat 26
• 3.3.1. Effect of the treatments on cell membrane integrity 26
• 3.3.2. Effect of the treatments on metabolic activity 26
• 3.3.3. Effect of the treatments on EMP pathway enzyme activities 28
• 3.4. Application of syringic acid, mild heat, and combination treatment in tomato juice 32
• 3.5. Color and lycopene content of tomato juice 34
• Ⅳ. DISCUSSIONS 38
• 4.1. Antimicrobial efficacy of SA + MH in different matrices 38
• 4.2. Matrix-dependent responses and possible interactions 38
• 4.3. Mechanistic insights: membrane disruption and cellular stress 40
• 4.4. Metabolic impairment: respiration and glycolytic enzymes 41
• 4.5. Overall mechanistic model and implications 42
• 4.6. Impact on product quality 42
• 4.7. Practical relevance and future perspectives 44
• Ⅴ. CONCLUSION 46
• ⅤI. REFERENCE 46
• ⅥI. 국문초록 50