Abstract This study examined factors that may affect the performance of a produce wash in preventing E. coli O157:H7 cross-contamination. Fresh-cut romaine lettuce (8 or 20 g) inoculated with ca. 7 log CFU/g of E. coli O157:H7 expressing green fluorescence protein was washed with uninoculated cut lettuce (800 or 2000 g) in 40 L of water for 2 min. Washing trials were performed in both sterile tap water and spent wash water collected from a commercial leafy greens processing facility under different prewash free chlorine levels (0, 5, 20 and 30 ppm), water temperatures (3 and 20 °C), leaf-to-water ratios (1:20 and 1:50), and flow rates (fast, medium, and slow). Performance of the chlorine wash was greatly affected by free chlorine level and wash water quality. Temperature, lettuce-to-water ratio, or water flow rate did not appear to have a significant impact. A prewash free chlorine concentration of 10 or 20 ppm was effective in preventing E. coli O157:H7 cross-contamination when lettuce was washed in tap water in the two washing systems assembled; 30 ppm of chlorine was needed to prevent cross-contamination during washing in industry water. Small-scale (100 ml) inactivation studies were performed to examine the impact of organic and solid contents (with the addition of lettuce juice and play sand) on the antimicrobial efficacy of chlorinated water. Increases in organic matter resulted in greater depletion of chlorine and the presence of solids enabled the pathogen to better survive chlorination; both led to a lower antimicrobial efficacy observed. ORP did not correlate linearly with free chlorine. E. coli O157:H7 cross-contamination was observed when ORP exceeded 650 mV, indicating that a threshold level of 650 mV may not ensure the safety of produce wash water. Since effective chlorine level is highly influenced by wash water quality, monitoring of produce washing systems may best be performed by measuring wash water quality in conjunction with rapid measurement of free chlorine.

中文翻译：

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在切生菜的收获后清洗过程中，影响氯清洗性能和监控防止大肠杆菌 O157:H7 交叉污染的因素

摘要 本研究调查了可能影响农产品清洗在防止大肠杆菌 O157:H7 交叉污染方面的性能的因素。鲜切的长叶莴苣（8 或 20 克）接种了约 7 log CFU/g 表达绿色荧光蛋白的大肠杆菌 O157:H7 用未接种的切丝生菜（800 或 2000 g）在 40 L 水中洗涤 2 分钟。在不同预洗游离氯水平（0、5、20 和 30 ppm）、水温（3 和 20 °C）、叶-水比（1:20 和 1:50）和流速（快、中、慢）。氯洗的性能受游离氯水平和洗涤水质的影响很大。温度，生菜与水的比例，或水流量似乎没有显着影响。在组装的两个洗涤系统中用自来水洗涤生菜时，10 或 20 ppm 的预洗游离氯浓度可有效防止大肠杆菌 O157:H7 交叉污染；需要 30 ppm 的氯来防止在工业用水洗涤过程中发生交叉污染。进行了小规模（100 毫升）灭活研究，以检查有机和固体含量（添加生菜汁和沙子）对氯化水的抗菌功效的影响。有机物的增加导致氯的消耗更大，固体的存在使病原体能够更好地在氯化中存活；两者都导致观察到的抗菌功效较低。ORP 与游离氯不呈线性相关。大肠杆菌 O157：当 ORP 超过 650 mV 时观察到 H7 交叉污染，表明 650 mV 的阈值水平可能无法确保生产洗涤水的安全。由于有效氯含量受洗涤水质量的影响很大，因此最好通过测量洗涤水质量并结合快速测量游离氯来监测产品洗涤系统。