Researchers have highlighted how cleaning frequency and hygiene in refrigerators can have a greater impact on food safety than short-term temperature differences.
Refrigerators with lower temperatures were not automatically microbiologically cleaner. The decisive factor was the cleaning frequency – particularly, the time since the last clean.
The team, led by Evelyne Selberherr from the Center for Food Sciences at the Veterinary University of Vienna (Vetmeduni), used high-resolution shotgun metagenomics to investigate the microbial communities on refrigerator surfaces in Austrian houses.
In 45 household fridges, shelves were sampled and other data such as refrigerator age, model, number of household members, presence of pets, time since last cleaning, cleaning frequency per year, sampled area, and items stored at the time of sampling was recorded.
Temperature findings
According to the study published in the journal LWT, results from a participant questionnaire showed many units were at least 15 years old. Only 17 out of 45 refrigerators maintained temperatures below 5 degrees C (41 degrees F), while 11 exceeded 7 degrees C (44.6 degrees F).
“The temperature measurements reveal a well-known but still relevant issue: only 38 per cent of the refrigerators examined were below the recommended threshold of 5 degrees C, while 24 per cent had temperatures exceeding 7 degrees C – a range considered an unfavorable worst-case scenario in the food industry and research,” said Selberherr.
Cleaning was specified as wiping the sampled shelf with a wet cloth or sponge, with or without the use of soap or disinfectants. Eight of 45 refrigerators were cleaned more than once per month. A few had been cleaned once or not at all in the past year.
Refrigerators that had not been cleaned for extended periods showed significantly higher microbial loads, lower species diversity, and a dominance of a few particularly adaptable microorganisms. Acinetobacter and spoilage-associated microbes dominated.
Cleaning importance
Findings suggest that hygiene practices have a more lasting impact than short-term temperature differences – an aspect that has been largely overlooked in consumer recommendations, said scientists.
Bacillus cereus was detected in 23 samples while Brucella was found 14 times. Yersinia intermedia, Campylobacter ureolyticus, and Listeria monocytogenes were each detected once.
“In 60 per cent of the refrigerators examined, potentially pathogenic bacteria were detected. The most common was Bacillus cereus, followed by Staphylococcus aureus,” said Moritz Hartmann, study lead author.
Results show that cross-contamination, through the direct placement of unpackaged food or hand contact, plays a central role. Cleaning intervals and handling practices appear to influence pathogen persistence more than temperature alone.
Selberherr said results suggest that measures such as regular cleaning have a significant impact on microbiological safety.
“These findings are relevant not only for private households, but also for sensitive supply areas such as hospital kitchens, care facilities, and communal catering. Especially in places where particularly vulnerable groups of people are cared for, the microbiological significance of refrigerators should be more strongly integrated into prevention strategies,” she said.”
Author: Joe Whitworth
Source: Food Safety News
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