O'Reilly C E, O'Connor P M, Kelly A L, Beresford T P, Murphy P M
Teagasc, Dairy Products Research Centre, Moorepark, Fermoy, County Cork, Republic of Ireland.
Appl Environ Microbiol. 2000 Nov;66(11):4890-6. doi: 10.1128/AEM.66.11.4890-4896.2000.
The objective of this study was to determine the effect of high pressure (HP) on the inactivation of microbial contaminants in Cheddar cheese (Escherichia coli K-12, Staphylococcus aureus ATCC 6538, and Penicillium roqueforti IMI 297987). Initially, cheese slurries inoculated with E. coli, S. aureus, and P. roqueforti were used as a convenient means to define the effects of a range of pressures and temperatures on the viability of these microorganisms. Cheese slurries were subjected to pressures of 50 to 800 MPa for 20 min at temperatures of 10, 20, and 30 degrees C. At 400 MPa, the viability of P. roqueforti in cheese slurry decreased by >2-log-unit cycles at 10 degrees C and by 6-log-unit cycles at temperatures of 20 and 30 degrees C. S. aureus and E. coli were not detected after HP treatments in cheese slurry of >600 MPa at 20 degrees C and >400 MPa at 30 degrees C, respectively. In addition to cell death, the presence of sublethally injured cells in HP-treated slurries was demonstrated by differential plating using nonselective agar incorporating salt or glucose. Kinetic experiments of HP inactivation demonstrated that increasing the pressure from 300 to 400 MPa resulted in a higher degree of inactivation than increasing the pressurization time from 0 to 60 min, indicating a greater antimicrobial impact of pressure. Selected conditions were subsequently tested on Cheddar cheese by adding the isolates to cheese milk and pressure treating the resultant cheeses at 100 to 500 MPa for 20 min at 20 degrees C. The relative sensitivities of the isolates to HP in Cheddar cheese were similar to those observed in the cheese slurry, i.e., P. roqueforti was more sensitive than E. coli, which was more sensitive than S. aureus. The organisms were more sensitive to pressure in cheese than slurry, especially with E. coli. On comparison of the sensitivities of the microorganisms in a pH 5.3 phosphate buffer, cheese slurry, and Cheddar cheese, greatest sensitivity to HP was shown in the pH 5.3 phosphate buffer by S. aureus and P. roqueforti while greatest sensitivity to HP by E. coli was exhibited in Cheddar cheese. Therefore, the medium in which the microorganisms are treated is an important determinant of the level of inactivation observed.
本研究的目的是确定高压（HP）对切达干酪中微生物污染物（大肠杆菌K-12、金黄色葡萄球菌ATCC 6538和罗克福青霉IMI 297987）灭活的影响。最初，接种了大肠杆菌、金黄色葡萄球菌和罗克福青霉的干酪匀浆被用作一种便捷手段，以确定一系列压力和温度对这些微生物活力的影响。将干酪匀浆在10℃、20℃和30℃的温度下，承受50至800MPa的压力20分钟。在400MPa时，10℃下干酪匀浆中罗克福青霉的活力下降超过2个对数单位循环，20℃和30℃时下降6个对数单位循环。在20℃下对干酪匀浆进行大于600MPa的高压处理以及在30℃下进行大于400MPa的高压处理后，分别未检测到金黄色葡萄球菌和大肠杆菌。除了细胞死亡外，通过使用添加了盐或葡萄糖的非选择性琼脂进行差异平板培养，证明了高压处理后的匀浆中存在亚致死损伤细胞。高压灭活的动力学实验表明，将压力从300MPa提高到400MPa比将加压时间从0分钟增加到60分钟导致更高程度的灭活，这表明压力具有更大的抗菌作用。随后，通过将分离菌株添加到干酪乳中，并在20℃下对所得干酪进行100至500MPa的压力处理20分钟，在切达干酪上测试了选定的条件。分离菌株在切达干酪中对高压的相对敏感性与在干酪匀浆中观察到的相似，即罗克福青霉比大肠杆菌更敏感，大肠杆菌比金黄色葡萄球菌更敏感。这些微生物在干酪中比在匀浆中对压力更敏感，尤其是大肠杆菌。在比较微生物在pH 5.3磷酸盐缓冲液、干酪匀浆和切达干酪中的敏感性时，金黄色葡萄球菌和罗克福青霉在pH 5.3磷酸盐缓冲液中对高压最敏感，而大肠杆菌在切达干酪中对高压最敏感。因此，处理微生物的介质是观察到的灭活水平的一个重要决定因素。
