Ukuku Dike O, Jin Tony, Zhang Howard
Food Safety Intervention Technologies Research Unit, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, USA.
J Food Prot. 2008 Oct;71(10):1988-95. doi: 10.4315/0362-028x-71.10.1988.
Bacterial injury, including leakage of intracellular substance and viability loss, of Escherichia coli K-12 (ATCC 23716) and Salmonella Enteritidis (ATCC 13076) inoculated in liquid egg white and liquid whole egg was determined by thermal death time disk. E. coli K-12 and Salmonella Enteritidis were inoculated in liquid egg white and liquid whole egg to a final count of 7.8 log CFU/ml and were thermally treated with thermal death time disks at room temperature (23"C), 54, 56, 58, and 60 degrees C from 0 to 240 s. Sublethal injury, leakage of intracellular substances, and viability loss of E. coli K-12 and Salmonella Enteritidis was investigated by plating 0.1 ml on selective trypticase soy agar containing 3% NaCl, 5% NaCl, sorbitol MacConky agar, and xylose lysine sodium tetradecylsulfate and nonselective trypticase soy agar. No significant (P > 0.05) differences on percent injury or viability loss for E. coli K-12 and Salmonella populations were determined in all samples treated at 23 degrees C. Sublethal injury occurred in E. coli and Salmonella populations at 54 degrees C or above for 120 s. Viability losses for both bacteria averaged 5 log at 54 degrees C or above for 180 s, and the surviving populations were below detection (<10 CFU/ml). Thermal treatment at 40 degrees C and above led to membrane damage, leakage, and accumulation of intracellular ATP from 2 to 2.5 log fg/ml and UV-absorbing substances of 0.1 to 0.39 in the treated samples. These results indicate similar thermal injury/damage on both E. coli and Salmonella membranes as determined by the amount of inactivation, viability loss, and leakage of intracellular substances of bacteria.
通过热致死时间圆盘法测定了接种于液态蛋清和液态全蛋液中的大肠杆菌K-12（美国典型培养物保藏中心23716）和肠炎沙门氏菌（美国典型培养物保藏中心13076）的细菌损伤情况，包括细胞内物质泄漏和活力丧失。将大肠杆菌K-12和肠炎沙门氏菌接种于液态蛋清和液态全蛋液中，使最终菌数达到7.8 log CFU/ml，并在室温（23℃）、54、56、58和60℃下用热致死时间圆盘进行0至240秒的热处理。通过将0.1 ml菌液接种在含有3%氯化钠、5%氯化钠、山梨醇麦康凯琼脂和木糖赖氨酸十四烷基硫酸钠的选择性胰蛋白酶大豆琼脂以及非选择性胰蛋白酶大豆琼脂上，研究了大肠杆菌K-12和肠炎沙门氏菌的亚致死损伤、细胞内物质泄漏和活力丧失情况。在23℃处理的所有样品中，大肠杆菌K-12和沙门氏菌群体的损伤百分比或活力丧失无显著（P>0.05）差异。在54℃及以上处理120秒时，大肠杆菌和沙门氏菌群体出现亚致死损伤。在54℃及以上处理180秒时，两种细菌的活力丧失平均为5 log，存活菌数低于检测限（<10 CFU/ml）。40℃及以上的热处理导致处理后样品中细胞膜损伤、泄漏，细胞内ATP积累量从2至2.5 log fg/ml，紫外线吸收物质含量从0.1至0.39。这些结果表明，根据细菌的灭活量、活力丧失和细胞内物质泄漏情况，大肠杆菌和沙门氏菌细胞膜的热损伤情况相似。
