|
Growers, packers and other sectors of the vegetable industry recognise that producing fresh, clean and safe products is a priority if markets are to be maintained and developed.
Quality assurance schemes have been introduced to help industry consistently manage quality.
However, in the area of postharvest hygiene, a lack of knowledge of contamination control and inconsistent interpretation of the regulations dealing with postharvest chemicals has caused a great deal of confusion.
This project report:
-
clarifies regulatory requirements for postharvest chemicals
-
provides comparative performance data and describe the factors influencing the performance of sanitisers
-
discusses the implications for washwater re-use and safe discharge with the object of assisting growers and packers better manage postharvest hygiene.
Good Agricultural Practices for hygienic postharvest are described.
Authors
|
Robert Holmes
|
Paul Harrup
|
Conclusions:
Our research demonstrated that sanitisers destroy up to 99% of harmful bacteria on fresh produce and totally eliminate bacterial and fungal pathogens from wash water.
However, the performance of washing systems depends on the quality of the supply water and the ability to control water quality in recirculated systems.
In particular, growers and packers may need to consider controlling the temperature, pH and organic load in their wash systems.
Another aspect of the project was to identify alternatives to chlorine and formalin as water and surface disinfectants respectively.
Chlorine dioxide, bromochlorine, ozone, peracetic acid, iodine, quaternary ammonia compounds, and non-chemical treatments were evaluated.
In partnership with manufacturers new hydrocooling and washing systems we developed and evaluated.
For many vegetable types, rapid establishment of the cold chain greatly reduces the risk of rots and microbiological contamination.
Workshops were held in five states to encourage the adoption of `best practice’ for hygienic postharvest and growers have been informed of project developments via a newsletter and booklet.
Regulation of sanitisers
-
Many growers have been confused about which sanitisers are legal to use in on-farm packing operations.
-
To some degree QA auditors and retail chains have contributed to this confusion by at times recognising only some of the legal sanitisers.
-
Growers and auditors need to be aware that chemicals supplied for postharvest washing, which claim to control spoilage organisms, either on the label or in the advertising material, are required to be registered with the NRA.
-
There are now 5 sanitisers for the postharvest washing of vegetables registered with the NRA.
-
There are also many general-purpose sanitisers excluded from the requirements of NRA approval (exempt).
-
These may be suitable for use on foods or for washing down equipment if they are approved for that purpose by Food Standards Australia New Zealand.
- We recommend that further work is done to increase the awareness by all sectors of the vegetable industry of the NRA and FSANZ regulations
Selection of appropriate sanitisers
-
In clean water, pathogens were reduced by 4 to 6-log10 by most sanitisers. Fungi were more resistant to sanitisers than bacteria.
-
In dirty water, only peroxyacetic acid (2% v/v) and chlorine dioxide (2.5mg/L) achieved greater than 4-log10 reductions of the most resistant fungus.
-
BCDMH and calcium hypochlorite are the most cost-effective actives to sanitise relatively clean wash water.
-
Chlorine dioxide is a more appropriate water sanitiser for the washing of dirty vegetables or vegetables which contribute a high organic load, such as brush-polished carrots.
-
Prewashing dirty vegetables in unsanitised water before a rinse in sanitised water will be an option for some growers, depending on water availability.
-
However prolonged soaking of vegetables in dirty and unsanitised water to remove soil increases the risk of rots.
-
This risk is highest where the produce is warmer than the water or the produce sinks in the water and is therefore more subject to infiltration by contaminated water.
-
A newly registered water treatment system, which uses iodine as the sanitiser, was highly effective in relatively clean water. We are not yet able to make any judgement of it’s cost efficiency.
-
All sanitisers were affected by pH in the range 5.5 to 8.5. Growers may therefore need information and products to assist pH control.
-
Surfaces were more difficult to sanitise than water and proved reactive, depleting sanitiser levels.
-
Peroxyacetic acid was the most effective on surfaces and especially superior on wood.
-
Other sanitisers can be used but because of the depletion, larger volumes are required if used at label rates.
-
Non chemical alternatives should be developed and evaluated such as solar pasteurisation and biofiltration of water and heat treatments for contact surfaces.
-
The addition of surfactants to reduce the surface tension on the microbial cell wall, improving sanitiser uptake, deserves further study.
-
For sanitisers depleted by organic and mineral load, flocculation followed by filtration is an option to improve economy of treatment.
-
The technologies and their cost effectiveness should be investigated with the objective to assist growers reduce the consumption of both water and sanitiser.
- For some sanitisers methods for pH management need investigation.
Recycling of used wash water
- More work is required to develop water treatment technologies to enable the efficient use and safe reuse of washwater, minimising water consumption and water discharge.
- Constructed wetlands may be functional, however many farms especially periurban farms do not have the required space.
General recommendations for hygienic postharvest
-
Wash vegetables only where there is a proven advantage.
-
Remove or trim off rotted plant parts before washing to minimise contaminating the wash water and remove trimmings from the grading/packing line as soon as possible.
-
Do not mix rotting produce with intact produce during harvest, handling or storage.
-
Clean and sanitise harvest, grading and packing equipment.
-
Test source water (and sanitise if contaminated) and sanitise recirculated wash and hydro-cooling water.
-
Maintain handling equipment so that mechanical damage to produce is minimised.
-
Encourage personal hygiene – provide clean toilet and hand washing facilities.
-
Cool chain reduces spoilage, but check for chilling injury in susceptible cultivars.
- Monitor critical control points. Refer to Guidelines for On-Farm Food Safety (Agriculture Fisheries and Forestry-Australia 2001)
Effectiveness of technology transfer
-
We estimate that 480 growers, packers and others attended the workshops and a further 200 received the field day handbooks on “Managing clean and safe water for washing vegetables”. This is less than one tenth of the industry.
-
We anticipate that some messages will diffuse further, however there will be a need for advisers to maintain an awareness of hygienic postharvest principles and methods to assist industry in the future.
- Many advisers need enhanced capabilities and resources to enable them to be effective consultants on these topics.
Other issues
-
The industry would benefit from a rapid test for microbial contamination.
-
Conventional tests (such as those used in this study) take several days and may not give an accurate assessment of the food safety status of stored vegetables.
-
For example, E. coli is very sensitive to sanitisers and therefore testing produce which has been sanitised, for the presence of this bacterium, may overlook the presence of other hazardous microorganisms.
Acknowledgments :
This project was funded by the Victorian Department of Primary Industries, the AusVeg levy, Horticulture Australia Limited, Queensland Fruit and Vegetable Growers (QFVG) – Tomato Sectional Group Committee; Northern Victoria Fresh Tomato Growers Association (NVFTGA); Avis Chemicals Pty Ltd, Wobelea Pty Ltd and Bioteq Ltd.
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.
Other key staff: Nam Ky Nguyen, Martin Mebalds, Dr Andrew Hamilton, Craig Murdoch; Institute for Horticultural Development, Knoxfield.
Grace Grech, Institute of Land and Food Resources, University of Melbourne
Lyn Jacka, Sally-Ann Henderson; Sunraysia Horticultural Centre, Irymple
Collaborators: Drs Alan McKay and Elaine Davison, Agriculture Western Australia Mark Hickey, Yanco Agricultural Institute, Yanco, New South Wales Helen Morgan, South Australian Research & Development Institute Craig Henderson, Queensland Department of Primary Industries
Industry Development Officers : Patrick Ulloa, David Ellement, Allison Anderson, Julia Telford and Craig Feutrill
|