Scientists urge caution despite flour test results

A study has found a low incidence of Salmonella and E. coli in flour in England, but researchers have stressed the importance of consumer awareness in avoiding infections.

Scientists looked at potential contamination of raw flour and raw flour-based products, such as pancake/batter mixes, with Salmonella, generic E. coli, and Shiga-toxin-producing E. coli (STEC).

Samples included flours available for sale in the UK from January to April 2020. 

Of the 882 flours sampled, one was positive for Salmonella. This sample contained multiple ingredients, such as flour, dried egg, and dried milk, and was milled in the UK.

A total of 68 samples contained generic E. coli at levels above 20 colony-forming units per gram (CFU/g). Analysis of flours revealed the presence of the Shiga-toxin (tx) gene in 10 samples, and STEC was isolated from seven. Five were from the UK, and five were imported.

None of the STEC flour isolates matched previous human cases, while the Salmonella Newport isolate from the mixed-ingredient product was similar to a human case from the UK in 2019.

Results published in the Journal of Applied Microbiology indicated that while the incidence was low, there is potential for Salmonella and STEC in flour. They will help inform future risk assessments on the consumption of raw flour products.

Potential risks highlighted
Researchers said their findings demonstrate the importance of raising awareness amongst food businesses and the public regarding the potential risks of consuming raw flour, dough, and batter.

Previous European and North American studies have found Salmonella or STEC in flour products, and outbreaks have been reported. The Centers for Disease Control and Prevention (CDC) runs a campaign advising people not to consume unbaked dough or batter.

Cereal grains are raw agricultural products grown outdoors, where they may be exposed to microbial pathogens in the soil and irrigation water or directly from birds and animals. These pathogens can represent a threat if they persist through processing steps into the final flour product.

The Food Standards Agency (FSA) says it is particularly important for vulnerable people, such as children under 5, those with compromised immune systems and older people, to not taste or eat raw dough or batter.

Samples of flour were collected from retailers, caterers, restaurants, and manufacturers by local authorities and examined by the UK Health Security Agency (UKHSA).

Of the 882 samples, 624 were produced in 40 different countries, including 476 from the UK, while 258 did not have a country of origin. Wheat was the most common grain, with 526 samples received, followed by rice with 53.

STEC types in flour were O26:H11, O36:H14, O155:H21, O156:H25, and O187:H28.

Regarding the Salmonella Newport positive from the Yorkshire pudding/pancake mix with multiple ingredients that matched a 2019 case, no epidemiological data suggests that this product had been consumed.

Scientists said safety messages on packs warning that flour and raw flour products, such as cake or pancake mixes, are considered raw ingredients and should not be consumed without cooking would help influence consumer behavior and reduce the potential risk of food poisoning.

(To sign up for a free subscription to Food Safety News, click here.)