USA – Researchers at Penn State University have developed a risk assessment model designed to help milk processors evaluate the potential consumer exposure to Bacillus cereus in high-temperature, short-time (HTST) pasteurized milk.

This model is expected to enhance milk safety decision-making by providing more precise data on the presence and growth of B. cereus in pasteurized milk.

HTST pasteurization is the predominant method used in the United States, but certain bacteria, including B. cereus, can withstand this process and pose health risks to consumers.

B. cereus, a group of eight species, varies in its implications for food spoilage and safety.

The new model created by Penn State researchers utilizes experimental growth data and models for different genotypes of toxin-producing B. cereus strains, allowing for a more accurate exposure assessment based on the growth potential of these strains in milk.

The model operates by allowing dairy processors to input data on the presence and quantities of B. cereus in milk. This data helps predict whether the pathogen is likely to propagate to levels that pose a high risk of exposure to consumers.

B. cereus concentrations of 100,000 cells per milliliter (mL) of milk are linked to foodborne illness, and the model can predict varying levels of bacterial concentration in milk containers.

The researchers tested the model and found that differences in B. cereus genotypes lead to varying levels of foodborne illness risk. For instance, while some genotypes would grow to the dangerous threshold of 100,000 cells per mL, the concentration per milk container could range from very low to significantly above this threshold.

Experimental growth data

To develop their model, researchers measured the growth of toxin-producing B. cereus strains in skim milk across gene profiles of six related bacteria groups with varying virulence. Their findings indicated that these strains did not grow in HTST pasteurized milk stored at 39°F or 43°F.

However, at 46°F, one strain grew; at 50°F, 15 strains grew; and at temperatures of 57°F or higher, all strains showed growth.

Using these initial growth data, secondary growth models and the exposure-assessment model were created. The model focuses on the HTST pasteurized milk supply chain and consumer storage for up to 35 days, starting with an initial contamination level of 100 cells per mL.

The model estimates that by day 21, 2.8 percent of milk containers could exceed dangerous levels of B. cereus, increasing to 4.1 percent by day 35.

Future applications

The research team is now developing open-access technology incorporating this model for use by food processors.

This system will enable users to enter detected bacterial concentrations and genotype information, providing predictions of the percentage of milk containers likely to carry B. cereus at dangerous levels.

Funded by the U.S. Department of Agriculture’s National Institute of Food and Agriculture (USDA’s NIFA), this project aims to advance food safety protocols by providing a robust tool for the dairy industry.

Implementing this model is anticipated to significantly reduce the risk of B. cereus exposure, safeguard consumer health, and ensure the quality of milk products.

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