A German risk assessment agency has issued an opinion after STEC was frequently found in flour samples.

Shiga toxin-producing E. coli (STEC) was detected in multiple flour samples (wheat, spelt and rye) from mills during routine food monitoring in Germany in 2018.

The Federal Ministry of Food and Agriculture (BMEL) asked the German Federal Institute for Risk Assessment (BfR) to assess the sources, risk and prevention of STEC in flour.

Fifty STEC-positive samples were detected in 328 wheat, spelt and rye flour samples analyzed in 2018 as part of the Federal Monitoring Plan. A product recall in November 2019 of ready-made dough for short pastry biscuits shows STEC can occur in such a product.

Investigations of flour samples from mills in Germany for STEC have shown between 10 and 21 percent have positive samples. Viable STEC of different serogroups are detectable in flour for more than 50 weeks.

Raw cookie dough
Between 2015 and 2019, the National Reference Laboratory for E. coli received 133 STEC isolates from flour, baking mixes and cereal waste. Excluding duplicates, 105 STEC isolates came from different types of wheat (n=62), rye (27) and spelt flour (five). Isolates comprised 27 different serotypes. Serotypes seen in human cases were isolated from rye and wheat flours and baking mixes and cereal waste.

BfR is planning a meeting with experts to discuss STEC, also known as enterohemorrhagic E. coli (EHEC), in flour. To estimate prevalence of STEC in flour at mill level in Germany, it may be included in zoonosis monitoring this year. Ready-made doughs could also be part of national monitoring programs.

Consumption of raw cookie dough plays a role in infections connected to STEC in flour. Other routes may include lack of kitchen hygiene and use of flour as a separating agent. Raw cookie dough is seen as a trendy food and is commercially offered in Germany. Commercially marketed cookie dough mixes for raw consumption are produced with pasteurized flour.

Two flour-associated outbreaks in the United States in 2016 and 2019 made more than 80 people sick and involved consumption of raw dough. No EHEC outbreaks attributable to flour based products have yet been reported in Germany. The likely match of a flour isolate with a human E. coli O157:H7 isolate, shows the presence of EHEC in flour is possible.

Lack of data on heat treated flour
Producers’ state there is no risk of infection to consumers posed by ready to use dough made from heat-treated or pasteurized flour. However, the BfR said as the parameters and technology of heat treatment are not known, it cannot be sure this assessment is correct.

The recommendation of heat treatment of a foodstuff for two minutes at a core temperature of 70 degrees C (158 degrees F) is not sufficient to safely kill STEC in flour using dry heat, according to the BfR.

STEC can be introduced into flour during wheat cultivation, harvest, storage, and processing of the grain. Processing steps include cleaning, tempering, grinding and packaging. Possible sources of contamination include soil, irrigation water and wildlife.

BfR recommendations to manufacturers of flours, baking mixtures and ready-made doughs include evaluating effectiveness of cleaning and disinfection plans on a regular basis via self-monitoring programs, heat treatment of ready-made dough for retail sale or production of ready-made dough from heat-treated flour, avoid and remove flour dust wher possible and avoid dusting of baked goods with flour after baking.

Risk mitigation measures, such as conditioning the grain with hot steam, treating it with ozone or UV radiation or irradiating ready-made doughs require technological development and research on effectiveness, influence on nutritional aspects and consumer acceptance.

Advice to consumers when handling flour, in addition to standard kitchen hygiene, includes before preparing food and after contact with flour, wash hands thoroughly with soap and water and dry carefully; avoid contact between flour and food for direct consumption, use different boards, plates, bowls and stirrers or wash them after contact with flour; clean surfaces and objects thoroughly with detergent and warm water after contact with flour, and dry them and do not eat unbaked cake and cookie dough.

BfR temperature revision for prepared food
Meanwhile, the BfR has studied minimum temperatures that must be maintained to prevent foodborne diseases. The analysis focused on the spore-forming bacteria of the Bacillus cereus group and Clostridium perfringens, which can multiply at high temperatures and are often the cause of illness associated with heated food.

In 2008, the BfR recommended keeping food warm at a temperature of at least 65 degrees C (149 degrees F). The agency is now advising to hold heated food hot so that it maintains an overall temperature of at least 60 degrees C (140 degrees F) prior to consumption.

Sufficiently heating food kills the vegetative cells of bacterial pathogens. Spores of pathogens, such as Bacillus cereus or Clostridium perfringens, can survive this preparation and, under certain conditions, re-germinate to produce vegetative cells and multiply.

The opinion also looked at the U.S. Food and Drug Administration’s (FDA) requirements in the 2017 Food Code which relate to keeping food hot. The BfR discusses whether the requirements are an alternative to its thinking for keeping food continuously hot, above a specified minimum temperature, in retail activities or catering processes by commercial kitchens. The relevant chapters cover controlled hot holding at 57 degrees C or 54 degrees C (135 degrees F or 129 degrees F) for roasts.

According to the BfR, temperatures of heated food should not fall below 60 degrees C in any part of the product during hot holding. For this reason, the FDA requirements are not a suitable alternative in the German agency’s opinion.