Until recently, food safety in fresh produce was primarily concerned with pesticide residues.
It was not commonly accepted that fresh produce could be associated with food borne disease outbreaks.
However, outbreaks of food bome disease linked to the consumption of vegetables and fruit in developed countries is becoming more common.
The number of documented fresh produce-related outbreaks in the USA more than doubled from between 1973 and 1987 to the period 1988 to 1991.
Bacterial diseases have been attributed to E. coli, Salmonella, Listeria, Shigella, Bacillus, Clostridium and Campylobacter.
Viruses and parasites have also been linked to produce-related disease outbreaks.
Consequently the fresh produce industry has had to deal with a lot of new issues revolving around a changing definition of food safety.
Many quality assurance systems have been introduced which encompass food safety to address the risks involved in production.
However, with this have come a lot of challenges. Uncertainty exists with regard to some of the technical aspects of on-farm food safety.
There has been much confusion and inconsistencies in the way systems have been implemented and audited because of a lack of information available on which to base these systems.
This project report address these issues.
The major outcome has been the production of a national food safety guide that the vegetable industry can use as a reference tool.
A farmgate survey of vegetables for human pathogens was carried out as part of this project.
Whilst there are many studies published overseas looking at isolation of different human pathogens on whole fresh produce, this data cannot be found in Australia.
We analysed around 200 vegetable samples from 35 farms in Victoria for a number of human pathogens.
The vegetables chosen were salad types and include cos lettuce, salad mix, celery, cabbage and Dutch carrots.
Overall incidence of pathogens found on the vegetable samples was low with one positive for Salmonella victoria and one for Listeria monocytogenes.
Whilst it is preferable not to find such pathogens it is also encouraging that the numbers found were low, particularly when comparisons are made with overseas studies of this type.
The effectiveness of calcium hypochlorite on inactivation of E coli inoculated on fresh produce was investigated.
Different times of exposure and concentrations of chlorine were studied. Dipping was not effective at eliminating E. coli populations although it significantly reduced the E. coli counts compared to inoculated, undipped lettuce.
Dipping inoculated cos lettuce leaves into hypochlorite solutions containing 50 mg/L or greater free chlorine for times of 30 seconds or greater reduced E. coli cells by approximately 1.9 to 2.8 log10 colony forming units per gram (CFU/g) from an initial population of approximately 6.8 log10 CFU/g.
Dipping lettuce in water alone reduced cell numbers by 1.7 log10 CFU/g.
Dipping inoculated broccoli florets into hypochlorite solution reduced E. coli cells by approximately 1.7 to 2.5 log10 CFU/g, depending on the time and concentration of the free chlorine in the wash water.
Dipping broccoli in water alone reduced cell numbers by 1.5 to 1.8 log10 CFU/g.
Dipping broccoli florets for 2 minutes in a 100 mg/L free chlorine solution at temperatures between 4 and 25°C reduced E. coli cells by approximately 2.4 log10 CFU/g.
No significant effect of temperature on the level of cell reduction was observed.
Water samples were collected from seven farms in three main growing areas of Victoria, Werribee, the Mornington Peninsula and East Gippsland.
Different water sources were looked at which included bore. dam. river and lake water.
All of the samples except for one fell within the current Australian water quality guidelines of 1000 faecal coliforms per 100 mL.
We found bore water to have much lower levels of faecal streptococci, faecal coliforms and E. coli than dam, river or channel water.
This is not that surprising since surface water could come from some distance and there may be less control over potential sources of contamination.
Most bore water samples had levels of faecal coliforms of less than 2 most probable number per 100mL (MPN/100mL), with the highest level being 14.
Channel/river water samples contained from less than 2 to 350 MPN/100mL.
Dam water had mainly between 5 to 540 MPN/100mL, with 2 samples containing 920 MPN/100mL faecal coliforms.
Consideration of this data resulted in a recommendation that soil on new land should contain less than 100 E. coli (CFU)/g.
We would like to thank John Faragher, Bruce Tomkins and Scott Ledger for their contribution as members of the project management team for the Safe Vegetable Production publication.
As well as the industry team members and those who reviewed the guide, these people are listed in the guide.
In addition, John Faragher for his advice and contribution towards developing the strawberry industry food safety guide.
Peter Franz for his help with the statistical analysis, Janet Tregenza for her technical assistance with the farmgate survey,
Susan Pascoe for her assistance in collection and analysis of the soil samples and the Microbiological Diagnostics Unit for help received in setting up the methodology for the irrigation water analyses.
This project was commissioned by Horticulture Australia Limited with funds frrom the Vegetable R&D levy and the Victorian State Government..
The Australian Government provides matched funding for all HAL’s R&D activities.