Consuming leftover pork chops carries a high risk for contracting Salmonella and Listeria infections if the meat was not originally cooked well-done, according to  new research.

A large percentage of people prefer their pork cooked medium, but a study published in Risk Analysis: An International Journal says that “cooking pork chops to an acceptable temperature does not completely eliminate pathogens, providing these cells with the opportunity to multiply during storage and harm consumers.”

The study can be found under the title “Impact of cooking procedures and storage practices at home on consumer exposure to Listeria monocytogenes and Salmonella due to the consumption of pork meat.”

Researchers found that the only way to completely eliminate Listeria and Salmonella pathogens was to cook pork loin chops well-done, in a static oven. Thus, cooking the meat to other levels like rare or medium still left surviving pathogen cells behind.

Likewise, even when satisfying the internal cooking temperature recommendation for pork — 165 degrees F — the research showed that stove-top cooking allowed pathogens to survive. Each scenario supports a breeding ground for bacteria when leftovers are stored for later use.

“It is generally believed that when meat is heat treated to 70 degrees Celsius (158 degrees Fahrenheit) for two minutes, a one million cell reduction of E. coli, Salmonella and Listeria is achieved and thus the meat is free of pathogens and safe to eat.” However, “a report by the European Food Safety Authority revealed that more than 57 percent of Salmonella outbreaks in 2014 were in the household/kitchen, and 13 percent were associated with inadequate heat treatment.”

Alessandra De Cesare, report author and professor at the University of Bologna, said “The results of this study can be combined with dose response models and included in guidelines for consumers on practices to be followed to manage cooking of pork meat at home.”

To accurately assess the pathogen levels in cooked pork, researchers tested 160 packs of loin chop for the study, which they experimentally contaminated with 10 million cells of L. monocytogenes and Salmonella to assess the reduction in pathogens after cooking.

According to the study, this was done in accordance with the Food Safety and Inspection Service (FSIS) and British Retail Consortium (BRC) specifications, “to ensure a reduction of at least 100,000 and 1,000,000 cells, respectively.” The samples were contaminated on the surface to mimic contamination occurring during slaughter and cutting.

“The samples were divided into groups to be cooked either on gas with a non-stick pan or in a static oven. In each setting, the pork chops were cooked to rare, medium and well-done. For each cooking combination, 40 repetitions were performed for a total of 240 cooking tests.”

To determine household consumer habits, reflecting “doneness preferences,” the researchers interviewed people ranging from 20 years old to 60 years old. The researchers used previously published data to define “meat storage practices” and the probability that consumers store their leftovers at room temperature, in the refrigerator, or discard them immediately.

Even for consumers who have good habits of promptly placing leftovers in the fridge, researchers note that “the few surviving cells can multiply during storage in both the refrigerator and at room temperature, reaching concentrations dangerous for both vulnerable and regular consumers.”

Ultimately, consumers should always remember to heat their pork to an internal temperature of 165 degrees F, while cooking it well-done, in a stove, to ensure the complete elimination of Salmonella or Listeria growth in the present, or future.

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