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Cheese Technology

Prevention of Salmonella in cheese and other dairy products

Dr. Mali Reddy

Dr. Mali Reddy serves as president of the American Dairy and Food Consulting Laboratories and International Media and Cultures (IMAC Inc.), Denver, Colorado. He holds several degrees including M.S. and Ph.D. degrees from Iowa State University in food technology and microbiology. He is a guest columnist for this week’s issue of Cheese Market News®.

The recent recalls of 4 million pounds of nonfat dry milk (NDM) produced by Valley Milk Products due to Salmonella contamination and recalls of cheese originating from Deutsch Käse Haus due to Listeria contamination have resulted in negative media coverage and shaken up the American cheese industry.

Recalls due to pathogens appear to be increasing despite the fact the industry has more quality control checkups than any other time in the history. The entire cheese and dairy food industry should look into this issue seriously because it is only getting worse every year.

This article is focused primarily on Salmonella, its characteristics and techniques to control it using proven natural biological technology. Salmonella is a gram-negative, rod-shaped, flagellated, non-spore forming facultative anaerobe belonging to the family enterobacteriaceae. It was named after Dr. Salmon, an American veterinary surgeon, in 1885. Salmonella is the most common cause of food poisoning responsible for more than 2-4 million illnesses in the United States alone each year, including 19,000 hospitalizations and 380 deaths. Symptoms of Salmonella infection include diarrhea, nausea, abdominal cramps, loose bloody stool and high fever of 100 to 102 degrees F. The incubation period is 6-72 hours after ingestion and duration of infection lasts 3-7 days.

In the dairy food industry we are more concerned about the nontyphoidal strains of Salmonella typhimurium and Salmonella enteritidis. The questions to be asked are, does Salmonella gain entrance into raw milk from cows, and does pasteurization kill the bacteria? Salmonella does gain entrance into raw milk from cows, and in the majority of cases pasteurization is adequate to kill it. However, according to the literature, some strains of Salmonella such as Salmonella senftenberg are extremely heat resistant and thus perhaps may survive pasteurization if their initial numbers are high in the raw milk.

In addition certain strains of Salmonella, engulfed by white blood cells, survive and stay alive within the white blood cells by producing specific enzymes and compounds. This is Salmonella’s most dangerous mechanism of survival. The strains of such Salmonella, which survive and stay in the white blood cells and thus make entry into raw milk, may survive pasteurization. In addition, several strains of Salmonella have developed multiple antibiotic resistance, and thus salmonellosis is getting to be a highly dangerous infection. Perhaps, a similar situation may be true with Listeria.

What are the worst salmonellosis cases recorded in the United States relating to the dairy industry? The largest outbreak of foodborne salmonellosis in the United States was in 1985, involving 16,000 confirmed cases in six states due to contaminated lowfat and whole fat milk produced at a dairy factory in Chicago.

Lately several salmonellosis cases have been recorded due to consumption of raw milk (both regular and organic). It goes to prove that more of the animal origin strains have been gaining entrance and surviving in the raw milk. The December 2016 recall of NDM is the most recent widely-publicized instance of contamination.

If some strains of Salmonella survive high heat treatments, how can we eliminate this problem in the raw milk itself? One way is activating the lactoperoxidase system (LP system) in raw milk. This can be done by using hydrogen peroxide producing food grade GRAS milk silo cultures. The use of milk silo cultures in raw milk, along with good plant sanitation, will significantly reduce Salmonella in NDM. Has it been proven before? Yes, under my watch, we have manufactured more than half a billion pounds of NDM in Kansas, Nebraska and Oklahoma plants for a period close to 10 years by judiciously using milk silo cultures in raw milk. We haven’t had problems due to Salmonella, Listeria or any pathogen, for that matter.

In the case of cheese, hypothetically if Salmonella survive pasteurization or get into milk after pasteurization, what can we do to control the pathogen? Inoculating the pasteurized milk in the vat (as early as milk starts flowing into the cheese vat) with fully-grown active liquid bulk starter culture along with its natural fermentation byproducts including bacteriocins may help. The bacteriocins and the bacterial growth end products (along with the metallic ions from phage resistant liquid bulk media) will inactivate the Salmonella bacteria during ripening, although they have a lipopolysaccharide protective layer. In addition, brine tanks should also be protected to eliminate pathogens.

Can Salmonella make its entry into cheese through the anticaking agents in the shred or packaging rooms?

Yes it can. Some individuals are chronic carriers of Salmonella and if such individual comes in contact with the anticaking agents (at the time of manufacturing such anticaking agents), especially dry blended products, the Salmonella can gain entrance into the anticaking agents and thus into the finished cheese. What should we do to eliminate such contamination? Use only low pH, high-heat spray dried anticaking agents, which are least handled by workers, to eliminate taking chances with the subdued pathogens, which are hard to enumerate using the standard testing procedures. Of course, the workers who are chronic carriers of Salmonella should not be allowed to handle the finished cheese.

Salmonella and other pathogens must be tackled with improved biological technology. In addition, all plant employees should go through a simplified training program regarding the basics of Salmonella and other pathogens such as Listeria. Too many recalls due to pathogens and subsequent negative publicity will significantly impact consumer confidence and thus the overall dairy commerce.

CMN

The views expressed by CMN’s guest columnists are their own opinions and do not necessarily reflect those of Cheese Market News®.

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