- 學位論文
建構高靜水壓處理與反式肉桂醛對沙門氏菌與李斯特菌在雞絞肉中之殺菌模型
Modeling the Inactivation of Salmonella and Listeria monocytogenes in Ground Chicken under High Hydrostatic Pressure in the Presence of trans-Cinnamaldehyde
摘要
美國國民健康與營養訪問調查（National Health and Nutrition Examination Survey, 1999-2016）指出，美國成年人口對禽類的攝取量首次超越長期居冠的非加工類紅肉。肉品食用傾向的轉移代表相關食品微生物危害風險的上升。本篇研究使用中央合成設計以瞭解高靜水壓處理（high hydrostatic pressure processing, 266-434 MPa; 3.3-11.7 min）與反式肉桂醛（trans-cinnamaldehyde, 0.016-0.084%, w/w）作為柵欄技術，對於減少雞絞肉中沙門氏菌與李斯特菌數量之效果，並依此實驗架構建立統計模型描述其變化，而後透過反應曲面分析獲得達成目標殺菌數所需之最佳因子設定（最低參數值）。考量到食品病原菌在亞致死狀態下仍具有代謝活性及致病力，雖無法在逆境中生成菌落，卻能夠在適當條件下修復損傷進而增殖，以選擇性培養基進行食品病原菌的檢測可能會高估食品加工技術的殺菌效果。經高靜水壓處理後，沙門氏菌之好氧性平板計數（aerobic plate count, APC）高出其選擇性培養基（Xylose-Lysine-Tergitol 4, XLT-4）讀數約1至2個對數循環（log colony-forming unit per gram）；李斯特菌在APC與其選擇性培養基（Polymyxin Acriflavin Lithium-chloride Ceftazidime Aesculin Mannitol, PALCAM）讀數間沒有顯著差異。在400 MPa以下，李斯特菌對高靜水壓的抗性較沙門氏菌強，然而此情形在高靜水壓處理加入反式肉桂醛後得到相反結果。保存試驗顯示，高靜水壓處理與反式肉桂醛抑制了李斯特菌在4 °C的生長達9天，並持續減少沙門氏菌達3.4個對數循環。以沙門氏菌與李斯特菌的減少作為變數之線性迴歸模型分別具有0.91與0.95之R2。非線性迴歸模型擴展了其因子設計的上下限，增加統計模型對目標殺菌數的描述範圍。依據模型預測與實驗證實，參數「372 MPa, 8.5 min, 0.07% tCinn」與「373 MPa, 8.0 min, 0.05% tCinn」分別減少沙門氏菌與李斯特菌5個對數循環。此外，掃描式電子顯微鏡影像呈現了病原菌經處理後的細胞結構變化。
並列摘要
This article investigated the impact of high hydrostatic pressure processing (HPP) in the presence of trans-cinnamaldehyde (tCinn) on the survival of Salmonella and Listeria monocytogenes in ground chicken meat, and developed statistical models, based on a central composite design (CCD), to quantify the microbial response to the imposed stress. The results demonstrated, at pressure level (266 to 434 MPa), processing time (3.3 to 11.7 min), and tCinn (0.016 to 0.084%, w/w), a 5-log reduction (colony-forming unit per gram) in the microbial population can be achieved. Due to the recovery of sublethally injured bacterial cells under proper growth conditions (e.g. nutrient-rich substrates, temperature, etc.), enumeration of foodborne pathogens using selective media may lead to an overestimation of process lethality. The viable count of HPP-stressed Salmonella demonstrated a 1- to 2-log difference between Xylose-Lysine-Tergitol 4 (XLT-4) agar and aerobic plate counts (APC), while there was no significant difference in that of HPP-stressed L. monocytogenes between Polymyxin Acriflavin Lithium-chloride Ceftazidime Aesculin Mannitol (PALCAM) agar and APC. Overall, L. monocytogenes was found more pressure-resistant than Salmonella at lower levels (< 400 MPa), but more susceptible to high-pressure treatments in the presence of tCinn. Post-treatment (HPP with tCinn) storage at 4 °C inhibited the growth of the surviving population of L. monocytogenes, and reduced that of Salmonella by 3.4 log at day 9. The R2 of Salmonella and L. monocytogenes linear regression models were 0.91 and 0.95, respectively. Dimensionless nonlinear models covered a factorial range slightly wider than the CCD-coded high- and low-end limits. As specified by ridge analysis, variable values targeting 5 log cycles of Salmonella and L. monocytogenes reduction were projected and verified at [372 MPa, 8.5 min, 0.07% tCinn], and [373 MPa, 8.0 min, 0.05% tCinn], respectively. In addition, structural changes of the bacterial cells treated with high pressure and tCinn were demonstrated in scanning electron microscope images.