As reported by the news, the Blue Bell Ice Cream facility that produced the ice cream with Listeria contamination had a stellar inspection. Surprising....no. Inspections are good for determining that procedures are being followed, the facility is clean, as well as other things that can be ascertained in a snapshot view of an operation, but low levels of contamination in these type of production facilities may not likely to be seen, and may even be hard for the facility to detect unless they were specifically looking...hard.
In many of the Listeria contamination issues we encounter, the issue is with post-lethality exposure of the product to the environment, or where the product receives no thermal treatment, but rather a wash (apples or cantaloupes). Listeria is a environmental pathogen that establishes itself in processing facility niches...in drains, in cooler air handling systems, in conveyor rollers, in washing flumes, and weighing equipment. A facility controls Listeria through good sanitation and verifies that cleanliness through monitoring the environment by environmental sampling/testing for Listeria.
But in the case of
humus or
ice cream, they are primarily closed systems. That is, after heating, the product is pumped through pipes, cooled to some degree, and filled. The product has little exposure to the external environment, except for perhaps open hoppers or at the filler. (This would not be a hazard of concern in hot filled product because the hot product provides lethal treatment all the way to the container).
Let's take a look at the hummus - Listeria issue. If you look at the process of making hummus (
a video of the process, not Sabra, but probably similar), the opportunities for cross contamination are limited. Looking at this video, the facility may not look sterile, but it is more important however that the pipes, transfer hopper, and filler are clean and sanitized, and that there are no niches where Listeria could gain a foothold. Thus, the fact that this product was found to be positive for Listeria probably indicates this type of in-line contamination. If that is the case, then it could either be improper cleaning of the process lines after a contamination event, or some niche developed within the line or at the filler (worn or torn gaskets in the filler or in the pumps, etc). Under-processing could also be an issue, but at least with the hummus, if this were the case, the product would be subject to spoilage.
Because these are closed systems, many facilities do not focus their testing as much on Listeria in finished product. They may test finished product to verify the pasteurization process is working properly, using general plate counts such as APC or coliforms, and maybe even Salmonella. But these will probably not necessarily give an indication of Listeria contamination. If Listeria is tested in the finished product, it is probably done using a small sample size, unlikely to detect a low level contamination issue. As for environmental testing, again the focus would probably be on verification of cleanliness by using ATP (an indicator used for microorganisms) or even general bacterial counts such as APC (aerobic plate count). Listeria testing, if done in the environment, would probably focus on non-contact surfaces. The presence or absence of Listeria in areas such as the drain may not raise a flag for indicating a contamination issue in finished product.
There are many who avoid doing finished product testing to any great degree for organisms like Listeria. But this is the type of organism, if present in a niche within this type of closed system, can grow due to the product / process type and serve as an ongoing contamination issue. To eliminate such a contamination, proper cleaning and sanitizing are critical, along with the removal of any niches including replacing gaskets and seals, filling cracks, etc.
To detect low level contamination, small sized samples (25 gram) may not be sufficient to accomplish detection. Large size samples (300 gm or 375gm) composited over the production run, or focused at the end of the run will be better for detection of such an issue. Another method, often cited by our good friend Dr. Steve Goodfellow, is to collect waste samples for analysis. Waste sample analysis uses the drips and drops that accumulate on the floor or on the exterior of the equipment throughout the production run. These can provide a worst-case-scenario for product and can be useful in determining a contamination issue.
Swabbing potential in-line harborage sites may also be helpful. This would include pinch points, dead ends in pipes, gaskets, seals, and filler nozzles. The downside of this is that contamination may emerge until the process has been running for a number of hours.
These two events are a reminder that Listeria contamination can be an issue where there is little to no environmental exposure of the product, and that detection of low level of contamination can be an issue.
Note - This supposition is based upon general practice and may not reflect the actual practices of the facilities mentioned.
MySanantonio.com
http://www.mysanantonio.com/news/texas/article/Number-of-people-sickened-by-listeria-outbreak-6188629.php
Inspection found no problem at Oklahoma ice cream plant
By DAVID WARREN and JUAN A. LOZANO, Associated Press : April 9, 2015 : Updated: April 9, 2015 7:26pm
DALLAS (AP) — Days after a foodborne illness was linked to Blue Bell ice cream products, a state inspection of an Oklahoma plant later tied to the infection praised the facility for having no violations and doing a "great job," according to a copy of the inspection report.
Inspectors had no reason to check for listeria during the routine March 18 review as no problems were detected and the facility didn't have a history of issues linked to the illness, said
Stan Stromberg, director of the food safety division for the Oklahoma
Department of Agriculture, Food and Forestry..
