Temperture changes and the threat of E. coli growth

Minced beef is one of the most common sources of foodborne infections, mainly because many people do not cook the product to high enough temperatures to kill off pathogens such as Salmonella, Listeria and E.Coli. However, outbreaks of E. coli have been traced to beef processors and regulatory developments are increasing pressure on processors to control bacterial pathogens during production.

Better understanding on the affect temperature fluctuations have on minced meat will help processors set critical limits for temperatures during grinding, say researchers.

The research, published in the August issue of the Journal of Food Protection, found that E. coli growth was not drastically affected by temperature changes in a set time period. There was little difference between meat held at low refrigeration temperatures and meat held at room temperatures during a six-hour period.

The researchers infected fresh ground beef samples with streptomycin-resistant E. coli and placed samples in four different environments. The samples were monitored at 4.4, 7.2, 10°C, and at room temperature (22.2 to 23.3°C). Researchers say that these temperatures are almost identical to those recorded in meat processing facilities.

The samples held under refrigeration were then examined for E. coli counts at 4, 8, 12, 24, 48, and 72-hour intervals. The room temperature samples were logged every two hours over a 12-hour period using tryptic soy agar, which is a culturing medium used to determine bacterial numbers.

Not surprisingly, samples held under refrigeration temperatures did not facilitate an increase in E. coli growth. E. coli did begin growing faster at 10°C but only after 48 hours, while samples held at 4.4 and 7.2°C maintained minimal growth during the entire 72 hour test.

However, samples held at room temperature did not witness an increase in E. coli until it passed the six-hour mark.

Researchers did note that after the 6-hour mark, E. coli levels in room temperature minced beef increased rapidly.

"These results illustrate that meat processors can utilize a variety of time and temperature combinations as critical limits in their hazard analysis critical control point plans to minimize E. coli O157:H7 growth during the production and storage of ground beef,"​ stated the report.

In Europe, pathogens such as E. coli lead to numerous sick days, needless deaths and large public health costs every year. It is estimated food born pathogens generate medical costs of more than €6bn a year in the EU.