There is little evidence to suggest a big change in microbial risk between freezing food on the use-by date compared to the day before, according to a review.

Food Standards Agency (FSA) guidance states that consumers can freeze pre-packed food up to the use-by date and, once food has been defrosted, it should be consumed within 24 hours.

A review looked at whether there was an increased risk in freezing ready-to-eat (RTE) and non-ready-to-eat foods on the use-by date compared to the day before.

It focused on how the shelf life of a food is determined and the effects of freezing, thawing and refrigeration on pathogens, including Bacillus spp., Campylobacter, Clostridium botulinum, Clostridium perfringens, Listeria monocytogenes, Salmonella, pathogenic E. coli and Shigella.

Minimal change to risk level
The review work considered the risks from consumer freezing, thawing and then refrigerated storage of food for 24 hours. Findings show growth of some pathogens during refrigeration is a possibility. Cooking to correct temperatures for non-RTE foods after defrosting eliminates certain pathogens.

There wasn’t much evidence to show a significant change in risk between consumers freezing food on the use-by date compared to freezing on the day before this date.

Ireland, New Zealand and Canada recommend including safety margins within shelf lives. There is no legal requirement in the UK to consider such a measure when setting shelf life.

Food businesses are responsible for setting the shelf life of food as part of their Hazard Analysis and Critical Control Point (HACCP) plan.

It is important that thawing is done as recommended in a microwave, a fridge or using cold water, rather than at room temperature, and that food is refrigerated or cooked straight after being defrosted. The type of food will determine pathogen growth and handling, cooking, and storage will also influence the likelihood of illness, according to the report.

Knowledge gaps
Although Bacillus cereus spores are heat resistant, there did not appear to be an increased risk as the lag time and growth rate at refrigeration temperatures are slow, making it unlikely to grow to levels capable of causing disease over a 24-hour period.

Clostridium botulinum spores are resistant to heat but there is likely to be limited growth and toxin production during freezing, thawing and storage at 8 degrees C (46.4 degrees F) for 24 hours. There is limited information on the effects of defrosting and subsequent refrigeration.

It is not clear whether there may be an increased risk from listeriosis from RTE foods frozen on the use-by date compared to RTE foods frozen the day before the use-by date. A review of literature on the effects of refrigeration, freezing and defrosting on Listeria monocytogenes showed there may be potential for concern, particularly for vulnerable groups where the infectious dose is low.

There is also a lack of research on the growth of Salmonella during domestic freezing and thawing.

More information on how food businesses set shelf life would enable a better understanding of the process and extent of the safety margin, according to the review.

Emerging technology impact
A different project looked at some emerging technologies that may impact the UK food system and food safety over the coming decade.

The report, produced by the University of Cambridge for the FSA, looked at food production and processing; novel sources of protein, such as insects; synthetic biology, including lab-grown meat; genomics applications; novel packaging; and digital technologies.

It found the FSA has to develop faster regulatory responses than in the past to ensure novel technologies do not compromise food safety and public health and to provide public confidence.

Food safety risks include exposure to novel production technologies and artificial farming environments, allergens, risk of food fraud, and potential misuse of synthetic biology and genomic tools. Online distribution platforms for food are the subject of a separate assessment.

Indoor farming could offer improved food safety but large-scale growing under artificial conditions presents new risks. Additional rules may be needed to prevent contamination and regulate indoor pesticide use.

For alternative sources of protein, research is required on microbial and hygienic safety, allergens, and toxicology. A shift toward reusable or zero packaging raises risks, and potential for exposure to pathogens, contamination, adulteration and food fraud.

Related emerging risks include changing consumer preferences for more raw and minimally-processed foods, microbial resistance to antibiotics and pesticides and climate change effects.

Positives include digital technologies improving food safety and traceability of production processes and supply chains, and techniques such as whole genome sequencing to find contamination issues and outbreaks quicker.

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