Experts have evaluated a range of methods to combat microbial hazards in fruit and vegetables.

The Joint FAO/WHO Expert Meetings on Microbial Risk Assessment (JEMRA) covered the prevention and control of microbiological hazards in fresh fruits and vegetables and provided scientific advice on ways to control such hazards from primary production to point-of-sale.

A summary of findings has been released but a full report will be published later as part of the FAO and WHO Microbiological Risk Assessment (MRA) series.

In 2019, the international Codex Alimentarius Commission approved work on the development of guidelines for the control of Shiga toxin-producing E. coli (STEC) in leafy vegetables and sprouts.

To support this, JEMRA held a series of meetings on preventing and controlling microbiological hazards in fresh fruits and vegetables. A meeting in September 2021 focused on ready-to-eat, and minimally processed fruits and vegetables, including leafy vegetables. Another event two months later looked at sprouts, from the production of seeds for sprouting to the point-of-sale.

Mitigation for fruits and vegetables
The aim was to evaluate commodity-specific interventions used at all stages of fruit and vegetable production from primary production to postharvest activities, transportation, point-of-sale, and consumer use. Experts considered the effectiveness, practicality, and suitability of interventions.

Four commodity groups were looked at: leafy vegetables and herbs; berries and tropical fruits; melons and tree fruits; and seeded and root vegetables.

For fruits and vegetables, scientists said preventive measures such as Good Agricultural Practices (GAP) and Good Hygiene Practices (GHP) during primary production remain the most effective means of reducing the risk of contamination. Postharvest activities require GHP, Good Manufacturing Practices (GMP), and a Hazard Analysis and Critical Control Point (HACCP) based system.

Irrigation water of poor or variable microbiological quality is a major risk factor during fruit and vegetable production, said experts.

They found public health data indicates that outbreaks caused by viral or parasitic pathogens are common, but research on interventions mainly addresses control of bacterial pathogens.

Methods such as UV, plasma, pulsed light and ultrasound show promise but there is little evidence of industry uptake. Experts said this could be because of practical reasons or performance in real-world settings.

Evaluation of interventions
Irradiation is the most effective postharvest treatment against pathogens on fresh-cut leafy vegetables but cost and consumer response is hindering commercial use.

Electrolyzed water with other physical treatments can reduce bacterial pathogens and bacteriophages also show potential but both have drawbacks, said experts.

For berries, water-assisted treatments like pulsed light had potential in some situations however, efficacy depends on how berries are inoculated. Gas-based methods such as controlled-release pads had variable effects depending on the dose and the pathogen assessed.

The main strategy for improving the safety of melons and tree fruits involves hygienic handling and hygiene control including environmental monitoring during sorting and packing. Water management is a key strategy to maintain the microbiological quality of process water and prevent cross-contamination.

Irradiation could also work on seeded and root vegetables but doses will need to be developed for commodity and target pathogen.

Gas phase chlorine dioxide treatment has shown efficacy on vegetables contaminated with pathogens and UV-C has promise for bacterial surface decontamination of vegetables.

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