Researchers from the University of Nebraska-Lincoln obtained 41 raw milk cheeses from retailers, farmers’ markets and online sources before analysing each for the presence of Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, Staphylococcus aureus, and Campylobacter.

The study, Survey of raw milk cheese for microbiological quality and prevalence of foodborne pathogens​, found that of the 41 samples, only three were contaminated with Staphylococcus aureus.

The current federal regulations state that raw milk cheeses may be manufactured and sold in the US providing the cheese is aged for at least 60 days at temperatures not less than 35˚F (1.7˚C).

However, there have been concerns among regulators due to the potential ability of foodborne pathogens to survive the manufacturing and aging process.

“Appear adequate”​

“To assess the microbiological safety of raw milk cheeses, we examined 41 different cheeses from sources around the US,” ​said the report.

“Importantly, all of the cheeses tested negative for the four major pathogens (E.coli O157:H7, L. monocytogenes, Salmonella, and Campylobacter) associated with recent raw milk cheese outbreaks.”​

“Based on the results obtained from these 41 raw milk cheeses, the 60-day aging rule for unpasteurised milk cheeses appears adequate for producing microbiologically safe products.”​

Despite the results, the report accepts that additional measures may be necessary to further ensure the safety of raw milk cheese products.

“Moreover, although the results from this study would appear to indicate that the current regulations for producing safe, high quality raw milk cheese are adequate, risk assessment models suggest that efforts aimed at improving hygiene and on-farm milk practices (i.e., by adoption of Good Manufacturing Practices and HACCP) can be even more effective at reducing risks of foodborne disease,” ​said the report.

Regulation review​

The current rule, which dates back to 1950 in the US Code of Federal Regulations, is based on the assumption that pathogenic organisms, even if present initially, would eventually die in the low pH, low water activity, high salt, competitive cheese environment during manufacturing.

Since its implementation, raw cheese has rarely been associated with foodborne illness in the US. However, in recent years, outbreaks of foodborne disease due to the consumption of raw milk cheese have become more frequent.

Several recent studies have shown that some pathogens can survive the manufacturing process and the 60 day aging period.

“As a result of these outbreaks and other reports, the US Food and Drug Administration (FDA) is now reviewing these regulations and have indicated that more strict requirements may be proposed. These changes may range from extension of the 60 day again period to outright rescinding of the regulation,” ​the report added.

ScienceDirect.com - Survey of raw milk cheeses for microbiological quality and prevalence of foodborne pathogens - J.C Brook, B. Martinez, J. Stratton, A. Bianchini, R. Krokstrom, R, Hutkins.​ http://dx.doi.org/10.1016/j.fm.2012.03.013​