Beuchat Larry R, Ryu Jee-Hoon, Adler Barbara B, Harrison M David
Center for Food Safety and Department of Food Science and Technology, University of Georgia, Griffin 30223-1797, USA.
J Food Prot. 2006 Apr;69(4):801-14. doi: 10.4315/0362-028x-69.4.801.
The objectives of this study were to determine the death rates of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in three commercially manufactured full-fat ranch salad dressings, three reduced-fat ranch salad dressings, two full-fat blue cheese salad dressings, and two reduced-fat blue cheese salad dressings and to affirm the expectation that these dressings do not support the growth of these pathogens. The respective initial pH values of the four types of shelf-stable, dairy-based, pourable dressings were 2.87 to 3.72, 2.82 to 3.19, 3.08 to 3.87, and 2.83 to 3.49, respectively. Dressings were inoculated with low (2.4 to 2.5 log CFU/g) and high (5.3 to 5.9 log CFU/g) populations of separate five-strain mixtures of each pathogen and stored at 25 degrees C for up to 15 days. Regardless of the initial inoculum population, all test pathogens rapidly died in all salad dressings. Salmonella was undetectable by enrichment (<1 CFU/25-ml sample in three replicate trials) in all salad dressings within 1 day, and E. coli O157:H7 and L. monocytogenes were reduced to undetectable levels by enrichment between 1 and 8 days and 2 and 8 days, respectively. E. coli O157:H7 was not detected in 4 of the 10 salad dressings stored for 2 or more days and 9 of the 10 dressings stored for 6 or more days after inoculation. L. monocytogenes was detected in 9 of the 10 salad dressings stored for 3 days but in only one dressing, by enrichment, at 6 days, indicating that it had the highest tolerance among the three pathogens to the acidic environment imposed by the dressings. Overall, the type of dressing (i.e., ranch versus blue cheese) and level of fat in the dressings did not have a marked effect on the rate of inactivation of pathogens. Total counts and populations of lactic acid bacteria and yeasts and molds remained low or undetectable (<1.0 log CFU/ml) throughout the 15-day storage period. Based on these observations, shelf-stable, dairy-based, pourable ranch and blue cheese salad dressings manufactured by three companies and stored at 25 degrees C do not support the growth of Salmonella, E. coli O157:H7, and L. monocytogenes and should not be considered as potentially hazardous foods (time-temperature control for safety foods) as defined by the U.S. Food and Drug Administration Food Code.
本研究的目的是测定三种市售全脂牧场沙拉酱、三种低脂牧场沙拉酱、两种全脂蓝纹奶酪沙拉酱和两种低脂蓝纹奶酪沙拉酱中沙门氏菌、大肠杆菌O157:H7和单核细胞增生李斯特菌的死亡率，并确认这些沙拉酱不支持这些病原体生长的预期。这四种货架稳定、以乳制品为基础的可倾倒沙拉酱各自的初始pH值分别为2.87至3.72、2.82至3.19、3.08至3.87和2.83至3.49。将每种病原体的单独五菌株混合物的低（2.4至2.5 log CFU/g）和高（5.3至5.9 log CFU/g）菌量接种到沙拉酱中，并在25℃下储存长达15天。无论初始接种菌量如何，所有测试病原体在所有沙拉酱中均迅速死亡。在1天内，所有沙拉酱中通过富集法均未检测到沙门氏菌（三次重复试验中<1 CFU/25 ml样品），大肠杆菌O157:H7和单核细胞增生李斯特菌分别在1至8天和2至8天通过富集法降至不可检测水平。接种后储存2天或更长时间的10种沙拉酱中有4种未检测到大肠杆菌O157:H7，储存6天或更长时间的10种沙拉酱中有9种未检测到。储存3天的10种沙拉酱中有9种检测到单核细胞增生李斯特菌，但在6天时通过富集法仅在一种沙拉酱中检测到，这表明它在三种病原体中对沙拉酱施加的酸性环境耐受性最高。总体而言，沙拉酱的类型（即牧场沙拉酱与蓝纹奶酪沙拉酱）和沙拉酱中的脂肪含量对病原体的失活速率没有显著影响。在整个15天的储存期内，乳酸菌、酵母菌和霉菌的总数及菌量保持较低水平或未检测到（<1.0 log CFU/ml）。基于这些观察结果，由三家公司生产并在25℃下储存的货架稳定、以乳制品为基础的可倾倒牧场沙拉酱和蓝纹奶酪沙拉酱不支持沙门氏菌、大肠杆菌O157:H7和单核细胞增生李斯特菌的生长，不应被视为美国食品药品监督管理局食品法典定义的潜在危害食品（安全食品的时间-温度控制）。
