U.S. Department of Agriculture, Agricultural Research Service, Environmental Microbial and Food Safety Laboratory, Beltsville, MD 20705, USA.
J Food Prot. 2011 Mar;74(3):352-8. doi: 10.4315/0362-028X.JFP-10-429.
This study was conducted to investigate the effect of free chlorine concentrations in wash water on Escherichia coli O157:H7 reduction, survival, and transference during washing of fresh-cut lettuce. The effectiveness of rewashing for inactivation of E. coli O157:H7 on newly cross-contaminated produce previously washed with solutions containing an insufficient amount of chlorine also was assessed. Results indicate that solutions containing a minimum of 0.5 mg/liter free chlorine were effective for inactivating E. coli O157:H7 in suspension to below the detection level. However, the presence of 1 mg/liter free chlorine in the wash solution before washing was insufficient to prevent E. coli O157:H7 survival and transfer during washing because the introduction of cut lettuce to the wash system quickly depleted the free chlorine. Although no E. coli O157:H7 was detected in the wash solution containing 5 mg/liter free chlorine before washing a mix of inoculated and uninoculated lettuce, low numbers of E. coli O157:H7 cells were detected on uninoculated lettuce in four of the seven experimental trials. When the prewash free chlorine concentration was increased to 10 mg/liter or greater, no E. coli O157:H7 transfer was detected. Furthermore, although rewashing newly cross-contaminated lettuce in 50 mg/liter free chlorine for 30 s significantly reduced (P = 0.002) the E. coli O157:H7 populations, it failed to eliminate E. coli O157:H7 on lettuce. This finding suggests that rewashing is not an effective way to correct for process failure, and maintaining a sufficient free chlorine concentration in the wash solution is critical for preventing pathogen cross-contamination.
本研究旨在调查洗涤水中游离氯浓度对清洗过程中大肠杆菌 O157:H7 减少、存活和转移的影响。还评估了重新洗涤对于减少先前用含氯量不足的溶液清洗过的新交叉污染的农产品上大肠杆菌 O157:H7 的效果。结果表明，含有至少 0.5 毫克/升游离氯的溶液可有效将悬浮液中的大肠杆菌 O157:H7 灭活至检测水平以下。然而，在洗涤前，洗涤水中存在 1 毫克/升的游离氯不足以防止大肠杆菌 O157:H7 在洗涤过程中存活和转移，因为将切好的生菜引入洗涤系统会迅速耗尽游离氯。尽管在洗涤前含有 5 毫克/升游离氯的洗涤水中未检测到大肠杆菌 O157:H7，但在七个实验试验中的四个试验中，在未接种的生菜上检测到低数量的大肠杆菌 O157:H7 细胞。当预洗游离氯浓度增加到 10 毫克/升或更高时，未检测到大肠杆菌 O157:H7 转移。此外，尽管用 50 毫克/升游离氯重新洗涤新交叉污染的生菜 30 秒可显著降低（P=0.002）大肠杆菌 O157:H7 种群，但未能消除生菜上的大肠杆菌 O157:H7。这一发现表明，重新洗涤不是纠正工艺失败的有效方法，保持洗涤水中足够的游离氯浓度对于防止病原体交叉污染至关重要。
