Peanut butter with that little bit extra

Over the last couple of weeks, Peanut Corp. of America has recalled 21 lots of peanut butter manufactured in its Blakely plant in Georgia. The product has been linked (by molecular biology techniques) with clusters of Salmonella infections in schools, long-term care facilities, hospitals and other institutions. Genetically indistinguishable strains have been isolated from the product and from patients. 470 people in 43 states have been confirmed as being infected with genetically indistinguishable strains of Salmonella Typhimurium and 90 have been hospitalized. Unfortunately, at least six deaths have been attributed to this outbreak.

The FDA has taken the extraordinary step of urging consumers to postpone eating any commercially prepared or manufactured products containing peanut butter and institutionally served peanut butter (because the implicated peanut butter is supplied only in bulk) until further information becomes available as to which products may be affected. Clearly, this will have far-reaching effects and we are already seeing voluntary recalls of various products in Tennessee, Indiana and New York.

How could this situation have arisen? This is not the first time that peanut butter has been linked with Salmonella infection. The New Zealand Food Safety Authority classes peanut butter as a prescribed (high risk) food because it is produced from peanuts, which have been found to contain mycotoxins (including aflatoxin), mould and insects. So the potential hazards are known. We need to go back and look at the process of peanut butter manufacture for a possible explanation of the current outbreak. The following description is something of a simplification:

Peanuts are actually groundnuts – the flower wilts and bends over, penetrating the ground. The peanut forms under the ground. Harvesting, cleaning and pre-preparation is an involved process, but the most important process is drying to a moisture content that prevents mould growth. The peanuts are shelled, roasted at around 175C and then cooled quickly to 30C. Any Salmonella present on the peanuts is by now destroyed. The peanuts are finely ground and sweetener, salt, oil if necessary and emulsifier are mixed in. The mix is hot filled at around 38C. A further pasteurization step in the jars in a hot water shower may be used here, but not always.

Now we can see where the problem may have arisen. Roasting and blanching are the only lethal process steps in the manufacture of peanut butter. Any contaminating microorganisms entering after these steps may survive in the finished product. Where could Salmonella come from? We don’t know about the Blakely plant yet, but birds often carry Salmonella, so strict control of birds and insects is required. Discharge of fines onto the roof of the factory may attract birds, which defecate on the roof. If the building is not well maintained, rain can wash the contaminating bacteria into the plant. A leaky roof and sprinkler system was the cause of an outbreak in February 2007 at the ConAgra Foods Inc. plant in Sylvester, Georgia. In that case, the Salmonella were thought to have come from raw peanuts or peanut dust. Equipment may harbour Salmonella in seals and hard-to-clean parts. Personnel may also carry Salmonella into the plant, either in their intestines or on footwear, so again, careful supervision of employee hygiene practices and use of red line areas in the post blanching operations is the way to control contamination.

It will be interesting to see what the FDA comes up with in the current investigation. When it’s all finished, this blog will carry a further article.