Abstract Activated persulfate is highly effective in inactivating foodborne pathogens. There is great potential to use this chemical in fresh produce sanitation. The present study evaluated the potential effect of organic load in fresh produce wash water on the bactericidal efficacy of activated persulfate. Romaine lettuce, iceberg lettuce, strawberries, and grapes were used to prepare the produce extracts which were later diluted with water to simulate produce wash water containing different levels of organic matters, represented by the Chemical Oxygen Demand (COD, 100–2000 mg/L). Ferrous activated persulfate (PS/Fe2+) and alkaline activated persulfate (PS/OH−) were prepared in simulated wash water. A five-strain cocktail of Escherichia coli O157:H7 was added to the activated persulfate solution and treated for 2 min. Water properties, including COD, phenolics, protein content, UV254 absorbance, turbidity, pH, and oxidation reduction potential (ORP), were measured and correlated to the microbial reductions. Trihalomethanes, one of the major types of chlorinated disinfection byproducts, were also monitored. Romaine lettuce inoculated with E. coli O157:H7 was used to validate the organic load effect. The results showed that the organic loads in wash water significantly reduced the effectiveness of bacterial inactivation. The microbial reduction decreased from over 8.0 log CFU/mL to near 2.0 log CFU/mL. The organic load had a significantly larger effect on PS/Fe2+ than on PS/OH−. Based on the correlation coefficients, COD, phenolics, and UV254 were found to be the major indicators to predict the organic load effect. However, since UV254 measurement was quicker, UV254 was used as the primary indicator for real produce (romaine lettuce) application. When UV254 was adjusted to 0.75 in the simulated wash water, lower reductions of E. coli O157:H7 on romaine lettuce and higher cross-contamination potentials were observed during washing with PS/Fe2+, PS/OH−, and NaOCl as compared with the lettuce in wash water without additional organic load. In addition, no significant amount of THMs was generated in simulated wash water spiked with produce extracts during activated persulfate treatment. In conclusion, to maintain a high efficacy of activated persulfate for fresh produce washing, the organic load of wash water must be carefully monitored. Activated persulfate is advantageous to traditional chlorine sanitizers as no toxic chlorinated disinfection by-products will be generated.

中文翻译：

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有机负荷对活化过硫酸盐灭活大肠杆菌 O157:H7 和卤化副产物产生的影响

摘要 活性过硫酸盐在灭活食源性病原体方面非常有效。在新鲜农产品卫生中使用这种化学物质有很大的潜力。本研究评估了新鲜农产品洗涤水中的有机负荷对活化过硫酸盐的杀菌功效的潜在影响。用长叶莴苣、卷心莴苣、草莓和葡萄制备农产品提取物，然后用水稀释以模拟含有不同水平有机物的农产品洗涤水，以化学需氧量（COD，100-2000 mg/L）为代表）。在模拟洗涤水中制备亚铁活化过硫酸盐 (PS/Fe2+) 和碱性活化过硫酸盐 (PS/OH-)。将大肠杆菌 O157:H7 的五株混合物加入到活化的过硫酸盐溶液中并处理 2 分钟。水属性，包括 COD、酚类物质、蛋白质含量、UV254 吸光度、浊度、pH 值和氧化还原电位 (ORP) 在内，都被测量并与微生物减少相关。三卤甲烷是氯化消毒副产品的主要类型之一，也受到了监测。用大肠杆菌 O157:H7 接种的长叶莴苣用于验证有机负荷效应。结果表明，洗涤水中的有机负荷显着降低了细菌灭活的有效性。微生物减少量从超过 8.0 log CFU/mL 降至接近 2.0 log CFU/mL。有机负荷对 PS/Fe2+ 的影响明显大于对 PS/OH- 的影响。基于相关系数，发现COD、酚类和UV254是预测有机负荷效应的主要指标。然而，由于 UV254 测量速度更快，UV254 被用作实际产品（长叶莴苣）应用的主要指示剂。当在模拟洗涤水中将 UV254 调整为 0.75 时，与使用 PS/Fe2+、PS/OH− 和 NaOCl 进行洗涤相比，在长叶莴苣上的大肠杆菌 O157:H7 减少较少，交叉污染可能性较高。生菜在洗涤水中没有额外的有机负荷。此外，在活化过硫酸盐处理过程中，在掺有农产品提取物的模拟洗涤水中没有产生大量的 THM。总之，要保持活化过硫酸盐对新鲜农产品洗涤的高效能，必须仔细监测洗涤水的有机负荷。活性过硫酸盐优于传统的氯消毒剂，因为不会产生有毒的氯化消毒副产品。