It’s called a chlorine monitor: If you wash fresh produce, buy one

Maintaining effective sanitizer concentration is of critical importance for preventing pathogen survival and transference during fresh-cut produce wash operation and for ensuring the safety of finished products. However, maintaining an adequate level of sanitizer in wash water can be challenging for processors due to the large organic load in the wash system.

tomato.dump.tankIn this study, we investigated how the survival of human pathogens was affected by the dynamic changes in water quality during chlorine depletion and replenishment in simulated produce washing operations. Lettuce extract was added incrementally into water containing pre-set levels of free chlorine to simulate the chlorine depletion process, and sodium hypochlorite was added incrementally into water containing pre-set levels of lettuce extract to simulate chlorine replenishment. Key water quality parameters were closely monitored and the bactericidal activity of the wash water was evaluated using three-strain cocktails of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes. In both chlorine depletion and replenishment processes, no pathogen survival was observed when wash water free chlorine level was maintained above 3.66 mg/L, irrespective of the initial free chlorine levels (10, 50, 100 and 200 mg/L) or organic loading (chemical oxidation demand levels of 0, 532, 1013 and 1705 mg/L). At this free chlorine concentration, the measured ORP was 843 mV and pH was 5.12 for the chlorine depletion process; the measured ORP was 714 mV and pH was 6.97 for the chlorine replenishment process.

 This study provides quantitative data needed by the fresh-cut produce industry and the regulatory agencies to establish critical operational control parameters to prevent pathogen survival and cross-contamination during fresh produce washing.

 Inactivation dynamics of Salmonella enterica, Listeria monocytogenes, and Escherichia coli O157:H7 in wash water during simulated chlorine depletion and replenishment processes

Food Microbiology, Volume 50, September 2015, Pages 88–96

Bin Zhou, Yaguang Luo, Xiangwu Nou, Shuxia Lyu, Qin Wang

Effects of post-harvest handling conditions on internalization and growth of Salmonella Enterica in tomatoes

Journal of Food Protection®, Number 3, March 2014, pp. 352-521 , pp. 365-370(6)

Zhou, Bin; Luo, Yaguang; Nou, Xiangwu; Yang, Yang; Wu, Yunpeng; Wang, Qin

Salmonella internalization in tomatoes during postharvest handling is a major food safety concern. This study was conducted to determine the effect of immersion time, immersion depth, and temperature differential between bacterial suspension and tomato pulp on the internalization of Salmonella enterica in tomato fruits. The effect of storage temperature and tomato.dump.tankduration on the survival and growth of internalized Salmonella cells was also evaluated. Overall, immersion time significantly affected the incidence and extent of S. enterica internalization (P < 0.0001), with a linear correlation between immersion time and Salmonella internalization. The depth of Salmonella internalization in tomato tissues also increased with increasing immersion time. Immersion time also significantly influenced the degree to which the temperature differential affected Salmonella internalization. With an immersion time of 2 min, the temperature differential had no significant effect on Salmonella internalization (P = 0.2536). However, with an immersion time of 15 min, a significantly larger Salmonella population became internalized in tomatoes immersed in solutions with a –30°F (–16.7°C) temperature differential. Internalized S. enterica cells persisted in the core tissues during 14 days of storage. Strain type and storage duration significantly affected (P < 0.05) both the frequency detected and the population of internalized Salmonella recovered, but storage temperatures of 55 to 70°F (12.8 to 21.1°C) did not (P > 0.05). These findings indicate the importance of preventing pathogen internalization during postharvest handling.


Listeria-linked farm had rated high in third-party audit

Chlorine is a wonderful thing when it comes to sanitation; especially with fresh produce. It’s also necessary to control dangerous bacteria, so it’s mind-numbing to hear a leading third-party auditor say that, based on the recommendations of staff who are supposed to know about food safety, that water does not have to be treated with something like chlorine.

Elizabeth Weise of USA Today reports that Jensen Farms, whose listeria-laden cantaloupes have killed 26 and sickened at least 123, got a top score — 96% — from a firm auditing the plant’s sanitation practices six days before the first person fell ill.

The rating has once again helped raise questions about the credibility of so-called third-party audits, a practice used increasingly by food sellers who hire auditing companies to check the safety and sanitation of the firms that sell them products and ingredients.

The Primus audit also gave only a mention to a change in how the fruit was washed, though one of the nation’s foremost cantaloupe safety experts, Trevor Suslow, calls it "unacceptable" and a clear violation of current industry practices.

Suslow, an expert on the post-harvest handling of produce at the University of California-Davis, said he was rendered "speechless" at news that Jensen was using untreated water to wash its melons.

The problem, which Suslow called a "red flag," was a switch by Jensen to a new fruit-washing system in July 2011. According to the FDA report and Gorny, that month Jensen Farms purchased and installed a used potato-washing machine to wash its cantaloupe.

According to the audit done by Primus Labs in August 2010, it appears that Jensen Farms had previously used a "hydro cooler" system to wash and cool the melons as they came in from the field, using recirculated water that was treated with an anti-microbial to kill bacteria.

For the 2011 harvest, the farm switched to a system in which cantaloupes were washed with fresh water that was not recirculated and "no anti-microbial solution is injected into the water of the wash station," the auditor, James DiIorio, noted on the first page of his audit.

"You would flat-out never do that, absolutely not," said Suslow, who spent more than six years researching cantaloupe safety and handling. No matter how clean the source of water is, once it’s sprayed on "any kind of surface where you have multiple produce items rolling across it, you’re trying to prevent cross-contamination … so you always add something to the water."

Suslow called this a "fundamental error with just tragic consequences. We can’t know that it absolutely made a difference, but I honestly think it could have prevented the scale and scope of what happened."

Robert Stovicek, president of Primus Labs, defended the audit, saying requiring that the wash water be treated with an anti-microbial is not "industry standard" at this time. He said his auditor, who so far has done 86 audits for Primus, did a good job in that he noted on page one of the audit that untreated water was being used. "He didn’t score them down but he commented on it," Stovicek said.
Audit companies do not set standards, he said. "We’re a company out there making observations and recording them."

Suslow and others disagree. Jensen Farms was "relying on people they consider knowledgeable and expert — that’s why they’re paying them," Suslow said.

Stovicek said that putting an anti-microbial agent such as chlorine in the water "certainly would retard any kind of spread. I think Trevor’s right to question that." But the Jensen Farms staff believed they were making an improvement in the safety when they switched to their new system. After the outbreak came to light, Stovicek consulted with his staff and they told him that water that’s not recirculated isn’t required to be treated. "I think Jensen’s will now go to sleep every night for the rest of their lives thinking, ‘Would that have made a difference?’"

The problems that were found at Jensen Farms are "Packing House 101," said Stephen Patricio, chairman of the California Cantaloupe Advisory Board. "Every common surface must be cleaned, rinsed and sanitized," he said. "These are all just known, recognized practices."

"It’s just disgusting to me," Patricio said of both Jensen Farms and Primus Labs. "I think of the damage that they’ve done to our industry as the result of this oversight. No, I won’t even talk about it as oversight, it’s abuse."