Each farm environment represents a unique combination that can influence occurrence and persistence of pathogens in leafy greens production, according to an EU scientific opinion.
Contamination can occur at any point in the farm-to-plate continuum, said EFSA Panel on Biological Hazards (BIOHAZ).
It is the first opinion out of five and addresses the risk from Salmonella and Norovirus in leafy greens eaten raw as salads.
“However, since leafy greens eaten raw as salads do not include any processing steps or control points which will ensure removal or inactivation of biological hazards, it is particularly important to consider risk factors (and consequentially mitigation options) at the point of production,” said the panel.
EFSA Panel on Biological Hazards (BIOHAZ), identified these products in the five top ranking groups of food/pathogen combinations according to specific EU criteria, and leafy greens eaten raw as salads were considered the highest priority in fresh produce safety.
Primary production pathogen risk
For Salmonella and Norovirus, processes at primary production which wet the edible portions of the crop represent the highest risk and these include spraying prior to harvest, direct application of fertilizers, pesticides and other agricultural chemicals and overhead irrigation.
Subsurface or drip irrigation which results in no wetting of the edible portions of the plants are of lower risk.
The panel said Salmonella contamination risks include environmental factors, contact with animal reservoirs, use of untreated or insufficiently treated manure or compost; contaminated agricultural water and cross-contamination by food handlers and equipment at harvest or on farm post-harvest.
Norovirus contamination risks at primary production were environmental factors, use of water for irrigation or pesticide treatment which has been contaminated by sewage and contamination by food handlers or equipment at harvest or on farm post-harvest.
Leafy greens can be further processed to get ready-to-eat products, including: selection, elimination of external leaves, cutting, washing, rinsing, dewatering, packaging and storage.
Other types of processing (e.g. freezing, mashing and unpasteurized juicing, blending etc) are either never or very rarely used with leafy greens and are not further considered in the opinion.
During processing, water submersion of fresh-cut leafy greens in washing tanks presents a risk of cross-contamination.
For Salmonella, this risk is reduced if disinfectants are properly used within the washing tank water
The effectiveness of chlorine against Norovirus is not fully defined due to the lack of an infectivity assay.
During processing, contamination or cross-contamination via equipment, water or by food handlers are the main risk factors for contamination for Salmonella and Norovirus.
Adherence or biofilm formation of Salmonella on processing equipment may become a source of contamination and be difficult to remove by routine cleaning methods.
Source: EFSA BIOHAZ Panel (EFSA Panel on Biological Hazards), 2014
Online, DOI: 10.2903/j.efsa.2014.3600
“Scientific Opinion on the risk posed by pathogens in food of non-animal origin. Part 2 (Salmonella and Norovirus in leafy greens eaten raw as salads)”